Apache Log4j 2 Users Guide

log4j-users-guide

User Manual:

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Table of Contents
Introduction
Architecture
Log4j 1.x Migration
API
Configuration
Web Applications and JSPs
Plugins
Lookups
Appenders
Layouts
Filters
Async Loggers
Garbage-free Logging
JMX
Logging Separation
Extending Log4j
Programmatic Log4j Configuration
Custom Log Levels

......................................................................................................................................

Apache Log4j 2

v. 2.11.0

User's Guide

......................................................................................................................................

The Apache Software Foundation 2018-03-17

Table of Contents i

Table of Contents

.......................................................................................................................................

1. Table of Contents ........................................................... i

2. Introduction ................................................................. 1

3. Architecture ................................................................. 3

4. Log4j 1.x Migration ........................................................ 10

5. API .......................................................................... 17

6. Configuration ............................................................... 20

7. Web Applications and JSPs .............................................. 59

8. Plugins ...................................................................... 68

9. Lookups .................................................................... 72

10. Appenders .................................................................. 80

11. Layouts .................................................................... 174

12. Filters ...................................................................... 210

13. Async Loggers ............................................................ 225

14. Garbage-free Logging .................................................... 239

15. JMX ........................................................................ 248

16. Logging Separation ....................................................... 255

17. Extending Log4j .......................................................... 257

18. Programmatic Log4j Configuration ...................................... 268

19. Custom Log Levels ....................................................... 276

Table of Contents ii

1 Introduction 1

1 Introduction

.......................................................................................................................................

1.1 Welcome to Log4j 2!

1.1.1 Introduction

Almost every large application includes its own logging or tracing API. In conformance with this

rule, the E.U. SEMPER project decided to write its own tracing API. This was in early 1996. After

countless enhancements, several incarnations and much work that API has evolved to become log4j,

a popular logging package for Java. The package is distributed under the Apache Software License,

a fully-fledged open source license certified by the open source initiative. The latest log4j version,

including full-source code, class files and documentation can be found at http://logging.apache.org/

log4j/2.x/index.html.

Inserting log statements into code is a low-tech method for debugging it. It may also be the only way

because debuggers are not always available or applicable. This is usually the case for multithreaded

applications and distributed applications at large.

Experience indicates that logging was an important component of the development cycle. It offers

several advantages. It provides precise context about a run of the application. Once inserted into the

code, the generation of logging output requires no human intervention. Moreover, log output can

be saved in persistent medium to be studied at a later time. In addition to its use in the development

cycle, a sufficiently rich logging package can also be viewed as an auditing tool.

As Brian W. Kernighan and Rob Pike put it in their truly excellent book "The Practice of

Programming":

As personal choice, we tend not to use debuggers beyond getting a stack trace or the value of a

variable or two. One reason is that it is easy to get lost in details of complicated data structures and

control flow; we find stepping through a program less productive than thinking harder and adding

output statements and self-checking code at critical places. Clicking over statements takes longer

than scanning the output of judiciously-placed displays. It takes less time to decide where to put print

statements than to single-step to the critical section of code, even assuming we know where that is.

More important, debugging statements stay with the program; debugging sessions are transient.

Logging does have its drawbacks. It can slow down an application. If too verbose, it can cause

scrolling blindness. To alleviate these concerns, log4j is designed to be reliable, fast and extensible.

Since logging is rarely the main focus of an application, the log4j API strives to be simple to

understand and to use.

1.1.2 Log4j 2

Log4j 1.x has been widely adopted and used in many applications. However, through the years

development on it has slowed down. It has become more difficult to maintain due to its need to be

compliant with very old versions of Java and became End of Life in August 2015. Its alternative,

SLF4J/Logback made many needed improvements to the framework. So why bother with Log4j 2?

Here are a few of the reasons.

1. Log4j 2 is designed to be usable as an audit logging framework. Both Log4j 1.x and Logback

will lose events while reconfiguring. Log4j 2 will not. In Logback, exceptions in Appenders are

never visible to the application. In Log4j 2 Appenders can be configured to allow the exception

to percolate to the application.

2. Log4j 2 contains next-generation Asynchronous Loggers based on the LMAX Disruptor library.

In multi-threaded scenarios Asynchronous Loggers have 10 times higher throughput and orders

of magnitude lower latency than Log4j 1.x and Logback.

1 Introduction 2

3. Log4j 2 is garbage free for stand-alone applications, and low garbage for web applications

during steady state logging. This reduces pressure on the garbage collector and can give better

response time performance.

4. Log4j 2 uses a Plugin system that makes it extremely easy to extend the framework by adding

new Appenders, Filters, Layouts, Lookups, and Pattern Converters without requiring any

changes to Log4j.

5. Due to the Plugin system configuration is simpler. Entries in the configuration do not require a

class name to be specified.

6. Support for custom log levels. Custom log levels can be defined in code or in configuration.

7. Support for lambda expressions. Client code running on Java 8 can use lambda expressions to

lazily construct a log message only if the requested log level is enabled. Explicit level checks are

not needed, resulting in cleaner code.

8. Support for Message objects. Messages allow support for interesting and complex constructs

to be passed through the logging system and be efficiently manipulated. Users are free to create

their own Message types and write custom Layouts, Filters and Lookups to manipulate

them.

9. Log4j 1.x supports Filters on Appenders. Logback added TurboFilters to allow filtering of

events before they are processed by a Logger. Log4j 2 supports Filters that can be configured to

process events before they are handled by a Logger, as they are processed by a Logger or on an

Appender.

10.Many Logback Appenders do not accept a Layout and will only send data in a fixed format.

Most Log4j 2 Appenders accept a Layout, allowing the data to be transported in any format

desired.

11.Layouts in Log4j 1.x and Logback return a String. This resulted in the problems discussed at

Logback Encoders. Log4j 2 takes the simpler approach that Layouts always return a byte array.

This has the advantage that it means they can be used in virtually any Appender, not just the ones

that write to an OutputStream.

12.The Syslog Appender supports both TCP and UDP as well as support for the BSD syslog and

the RFC 5424 formats.

13.Log4j 2 takes advantage of Java 5 concurrency support and performs locking at the lowest level

possible. Log4j 1.x has known deadlock issues. Many of these are fixed in Logback but many

Logback classes still require synchronization at a fairly high level.

14.It is an Apache Software Foundation project following the community and support model used

by all ASF projects. If you want to contribute or gain the right to commit changes just follow the

path outlined at Contributing.

2 Architecture 3

2 Architecture

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2.1 Architecture

2.1.1 Main Components

Log4j uses the classes shown in the diagram below.

Applications using the Log4j 2 API will request a Logger with a specific name from the LogManager.

The LogManager will locate the appropriate LoggerContext and then obtain the Logger from it. If the

Logger must be created it will be associated with the LoggerConfig that contains either a) the same

name as the Logger, b) the name of a parent package, or c) the root LoggerConfig. LoggerConfig

objects are created from Logger declarations in the configuration. The LoggerConfig is associated

with the Appenders that actually deliver the LogEvents.

2.1.1.1 Logger Hierarchy

The first and foremost advantage of any logging API over plain System.out.println resides in

its ability to disable certain log statements while allowing others to print unhindered. This capability

assumes that the logging space, that is, the space of all possible logging statements, is categorized

according to some developer-chosen criteria.

In Log4j 1.x the Logger Hierarchy was maintained through a relationship between Loggers. In Log4j

2 this relationship no longer exists. Instead, the hierarchy is maintained in the relationship between

LoggerConfig objects.

Loggers and LoggerConfigs are named entities. Logger names are case-sensitive and they follow the

hierarchical naming rule:

Named Hierarchy

2 Architecture 4

A LoggerConfig is said to be an ancestor of another LoggerConfig if its name followed

by a dot is a prefix of the descendant logger name. A LoggerConfig is said to be a parent

of a child LoggerConfig if there are no ancestors between itself and the descendant

LoggerConfig.

For example, the LoggerConfig named "com.foo" is a parent of the LoggerConfig named

"com.foo.Bar". Similarly, "java" is a parent of "java.util" and an ancestor of

"java.util.Vector". This naming scheme should be familiar to most developers.

The root LoggerConfig resides at the top of the LoggerConfig hierarchy. It is exceptional in

that it always exists and it is part of every hierarchy. A Logger that is directly linked to the root

LoggerConfig can be obtained as follows:

Logger logger = LogManager.getLogger(LogManager.ROOT_LOGGER_NAME);

Alternatively, and more simply:

Logger logger = LogManager.getRootLogger();

All other Loggers can be retrieved using the LogManager.getLogger static method by passing the

name of the desired Logger. Further information on the Logging API can be found in the Log4j 2

API.

2.1.1.2 LoggerContext

The LoggerContext acts as the anchor point for the Logging system. However, it is possible to have

multiple active LoggerContexts in an application depending on the circumstances. More details on the

LoggerContext are in the Log Separation section.

2.1.1.3 Configuration

Every LoggerContext has an active Configuration. The Configuration contains all the Appenders,

context-wide Filters, LoggerConfigs and contains the reference to the StrSubstitutor. During

reconfiguration two Configuration objects will exist. Once all Loggers have been redirected to the

new Configuration, the old Configuration will be stopped and discarded.

2.1.1.4 Logger

As stated previously, Loggers are created by calling LogManager.getLogger. The Logger itself

performs no direct actions. It simply has a name and is associated with a LoggerConfig. It extends

AbstractLogger and implements the required methods. As the configuration is modified Loggers may

become associated with a different LoggerConfig, thus causing their behavior to be modified.

2.Retrieving Loggers

Calling the LogManager.getLogger method with the same name will always return a reference to

the exact same Logger object.

For example, in

Logger x = LogManager.getLogger("wombat");

Logger y = LogManager.getLogger("wombat");

x and y refer to exactly the same Logger object.

Configuration of the log4j environment is typically done at application initialization. The preferred

way is by reading a configuration file. This is discussed in Configuration.

Log4j makes it easy to name Loggers by software component. This can be accomplished by

instantiating a Logger in each class, with the logger name equal to the fully qualified name of the

2 Architecture 5

class. This is a useful and straightforward method of defining loggers. As the log output bears the

name of the generating Logger, this naming strategy makes it easy to identify the origin of a log

message. However, this is only one possible, albeit common, strategy for naming loggers. Log4j does

not restrict the possible set of loggers. The developer is free to name the loggers as desired.

Since naming Loggers after their owning class is such a common idiom, the convenience method

LogManager.getLogger() is provided to automatically use the calling class's fully qualified class

name as the Logger name.

Nevertheless, naming loggers after the class where they are located seems to be the best strategy

known so far.

2.1.1.5 LoggerConfig

LoggerConfig objects are created when Loggers are declared in the logging configuration. The

LoggerConfig contains a set of Filters that must allow the LogEvent to pass before it will be passed to

any Appenders. It contains references to the set of Appenders that should be used to process the event.

2.Log Levels

LoggerConfigs will be assigned a Log Level. The set of built-in levels includes TRACE, DEBUG,

INFO, WARN, ERROR, and FATAL. Log4j 2 also supports custom log levels. Another mechanism

for getting more granularity is to use Markers instead.

Log4j 1.x and Logback both have the concept of "Level Inheritance". In Log4j 2, Loggers and

LoggerConfigs are two different objects so this concept is implemented differently. Each Logger

references the appropriate LoggerConfig which in turn can reference its parent, thus achieving the

same effect.

Below are five tables with various assigned level values and the resulting levels that will be associated

with each Logger. Note that in all these cases if the root LoggerConfig is not configured a default

Level will be assigned to it.

Logger Name Assigned

LoggerConfig LoggerConfig Level Logger Level

root root DEBUG DEBUG

X root DEBUG DEBUG

X.Y root DEBUG DEBUG

X.Y.Z root DEBUG DEBUG

Example 1

In example 1 above, only the root logger is configured and has a Log Level. All the other Loggers

reference the root LoggerConfig and use its Level.

Logger Name Assigned

LoggerConfig LoggerConfig Level Level

root root DEBUG DEBUG

X X ERROR ERROR

X.Y X.Y INFO INFO

X.Y.Z X.Y.Z WARN WARN

2 Architecture 6

Example 2

In example 2, all loggers have a configured LoggerConfig and obtain their Level from it.

Logger Name Assigned

LoggerConfig LoggerConfig Level Level

root root DEBUG DEBUG

X X ERROR ERROR

X.Y X ERROR ERROR

X.Y.Z X.Y.Z WARN WARN

Example 3

In example 3, the loggers root, X and X.Y.Z each have a configured LoggerConfig with the same

name. The Logger X.Y does not have a configured LoggerConfig with a matching name so uses the

configuration of LoggerConfig X since that is the LoggerConfig whose name has the longest match to

the start of the Logger's name.

Logger Name Assigned

LoggerConfig LoggerConfig Level level

root root DEBUG DEBUG

X X ERROR ERROR

X.Y X ERROR ERROR

X.Y.Z X ERROR ERROR

Example 4

In example 4, the loggers root and X each have a Configured LoggerConfig with the same name.

The loggers X.Y and X.Y.Z do not have configured LoggerConfigs and so get their Level from the

LoggerConfig assigned to them, X, since it is the LoggerConfig whose name has the longest match to

the start of the Logger's name.

Logger Name Assigned

LoggerConfig LoggerConfig Level level

root root DEBUG DEBUG

X X ERROR ERROR

X.Y X.Y INFO INFO

X.YZ X ERROR ERROR

Example 5

In example 5, the loggers root. X, and X.Y each have a Configured LoggerConfig with the same

name. The logger X.YZ does not have configured LoggerConfig and so gets its Level from the

LoggerConfig assigned to it, X, since it is the LoggerConfig whose name has the longest match to the

start of the Logger's name. It is not associated with LoggerConfig X.Y since tokens after periods must

match exactly.

2 Architecture 7

Logger Name Assigned

LoggerConfig LoggerConfig Level Level

root root DEBUG DEBUG

X X ERROR ERROR

X.Y X.Y ERROR

X.Y.Z X.Y ERROR

Example 6

In example 6, LoggerConfig X.Y it has no configured level so it inherits its level from LoggerConfig

X. Logger X.Y.Z uses LoggerConfig X.Y since it doesn't have a LoggerConfig with a name that

exactly matches. It too inherits its logging level from LoggerConfig X.

The table below illustrates how Level filtering works. In the table, the vertical header shows the

Level of the LogEvent, while the horizontal header shows the Level associated with the appropriate

LoggerConfig. The intersection identifies whether the LogEvent would be allowed to pass for further

processing (Yes) or discarded (No).

Event

Level LoggerConfig

Level

TRACE DEBUG INFO WARN ERROR FATAL OFF

ALL YES YES YES YES YES YES NO

TRACE YES NO NO NO NO NO NO

DEBUG YES YES NO NO NO NO NO

INFO YES YES YES NO NO NO NO

WARN YES YES YES YES NO NO NO

ERROR YES YES YES YES YES NO NO

FATAL YES YES YES YES YES YES NO

OFF NO NO NO NO NO NO NO

2.1.1.6 Filter

In addition to the automatic log Level filtering that takes place as described in the previous section,

Log4j provides Filters that can be applied before control is passed to any LoggerConfig, after

control is passed to a LoggerConfig but before calling any Appenders, after control is passed to a

LoggerConfig but before calling a specific Appender, and on each Appender. In a manner very similar

to firewall filters, each Filter can return one of three results, Accept, Deny or Neutral. A response

of Accept means that no other Filters should be called and the event should progress. A response of

Deny means the event should be immediately ignored and control should be returned to the caller. A

response of Neutral indicates the event should be passed to other Filters. If there are no other Filters

the event will be processed.

Although an event may be accepted by a Filter the event still might not be logged. This can happen

when the event is accepted by the pre-LoggerConfig Filter but is then denied by a LoggerConfig filter

or is denied by all Appenders.

2 Architecture 8

2.1.1.7 Appender

The ability to selectively enable or disable logging requests based on their logger is only part of the

picture. Log4j allows logging requests to print to multiple destinations. In log4j speak, an output

destination is called an Appender. Currently, appenders exist for the console, files, remote socket

servers, Apache Flume, JMS, remote UNIX Syslog daemons, and various database APIs. See the

section on Appenders for more details on the various types available. More than one Appender can be

attached to a Logger.

An Appender can be added to a Logger by calling the addLoggerAppender method of the current

Configuration. If a LoggerConfig matching the name of the Logger does not exist, one will be created,

the Appender will be attached to it and then all Loggers will be notified to update their LoggerConfig

references.

Each enabled logging request for a given logger will be forwarded to all the appenders in

that Logger's LoggerConfig as well as the Appenders of the LoggerConfig's parents. In other

words, Appenders are inherited additively from the LoggerConfig hierarchy. For example, if a

console appender is added to the root logger, then all enabled logging requests will at least print

on the console. If in addition a file appender is added to a LoggerConfig, say C, then enabled

logging requests for C and C's children will print in a file and on the console. It is possible to

override this default behavior so that Appender accumulation is no longer additive by setting

additivity="false" on the Logger declaration in the configuration file.

The rules governing appender additivity are summarized below.

Appender Additivity

The output of a log statement of Logger L will go to all the Appenders in the LoggerConfig

associated with L and the ancestors of that LoggerConfig. This is the meaning of the term

"appender additivity".

However, if an ancestor of the LoggerConfig associated with Logger L, say P, has the

additivity flag set to false, then L's output will be directed to all the appenders in L's

LoggerConfig and it's ancestors up to and including P but not the Appenders in any of the

ancestors of P.

Loggers have their additivity flag set to true by default.

The table below shows an example:

Logger

Name Added

Appenders Additivity

Flag Output Targets Comment

root A1 not applicable A1 The root logger

has no parent so

additivity does not

apply to it.

x A-x1, A-x2 true A1, A-x1, A-x2 Appenders of "x"

and root.

x.y none true A1, A-x1, A-x2 Appenders of "x"

and root. It would

not be typical to

configure a Logger

with no Appenders.

x.y.z A-xyz1 true A1, A-x1, A-x2, A-

xyz1 Appenders in

"x.y.z", "x" and root.

2 Architecture 9

security A-sec false A-sec No appender

accumulation since

the additivity flag is

set to false.

security.access none true A-sec Only appenders of

"security" because

the additivity flag in

"security" is set to

false.

2.1.1.8 Layout

More often than not, users wish to customize not only the output destination but also the output

format. This is accomplished by associating a Layout with an Appender. The Layout is responsible

for formatting the LogEvent according to the user's wishes, whereas an appender takes care of sending

the formatted output to its destination. The PatternLayout, part of the standard log4j distribution, lets

the user specify the output format according to conversion patterns similar to the C language printf

function.

For example, the PatternLayout with the conversion pattern "%r [%t] %-5p %c - %m%n" will output

something akin to:

176 [main] INFO org.foo.Bar - Located nearest gas station.

The first field is the number of milliseconds elapsed since the start of the program. The second field

is the thread making the log request. The third field is the level of the log statement. The fourth field

is the name of the logger associated with the log request. The text after the '-' is the message of the

statement.

Log4j comes with many different Layouts for various use cases such as JSON, XML, HTML, and

Syslog (including the new RFC 5424 version). Other appenders such as the database connectors fill in

specified fields instead of a particular textual layout.

Just as importantly, log4j will render the content of the log message according to user specified

criteria. For example, if you frequently need to log Oranges, an object type used in your current

project, then you can create an OrangeMessage that accepts an Orange instance and pass that to Log4j

so that the Orange object can be formatted into an appropriate byte array when required.

2.1.1.9 StrSubstitutor and StrLookup

The StrSubstitutor class and StrLookup interface were borrowed from Apache Commons Lang

and then modified to support evaluating LogEvents. In addition the Interpolator class was borrowed

from Apache Commons Configuration to allow the StrSubstitutor to evaluate variables that from

multiple StrLookups. It too was modified to support evaluating LogEvents. Together these provide

a mechanism to allow the configuration to reference variables coming from System Properties, the

configuration file, the ThreadContext Map, StructuredData in the LogEvent. The variables can either

be resolved when the configuration is processed or as each event is processed, if the component is

capable of handling it. See Lookups for more information.

3 Log4j 1.x Migration 10

3 Log4j 1.x Migration

.......................................................................................................................................

3.1 Migrating from Log4j 1.x

3.1.1 Using the Log4j 1.x bridge

Perhaps the simplest way to convert to using Log4j 2 is to replace the log4j 1.x jar file with Log4j

2's log4j-1.2-api.jar. However, to use this successfully applications must meet the following

requirements:

1. They must not access methods and classes internal to the Log4j 1.x implementation such as

Appenders, LoggerRepository or Category's callAppenders method.

2. They must not programmatically configure Log4j.

3. They must not configure by calling the classes DOMConfigurator or

PropertyConfigurator.

3.1.2 Converting to the Log4j 2 API

For the most part, converting from the Log4j 1.x API to Log4j 2 should be fairly simple. Many of the

log statements will require no modification. However, where necessary the following changes must be

made.

1. The main package in version 1 is org.apache.log4j, in version 2 it is

org.apache.logging.log4j

2. Calls to org.apache.log4j.Logger.getLogger() must be modified to

org.apache.logging.log4j.LogManager.getLogger().

3. Calls to org.apache.log4j.Logger.getRootLogger() or

org.apache.log4j.LogManager.getRootLogger() must be replaced with

org.apache.logging.log4j.LogManager.getRootLogger().

4. Calls to org.apache.log4j.Logger.getLogger that accept a LoggerFactory must

remove the org.apache.log4j.spi.LoggerFactory and use one of Log4j 2's other

extension mechanisms.

5. Replace calls to org.apache.log4j.Logger.getEffectiveLevel() with

org.apache.logging.log4j.Logger.getLevel().

6. Remove calls to org.apache.log4j.LogManager.shutdown(), they are not needed in

version 2 because the Log4j Core now automatically adds a JVM shutdown hook on start up to

perform any Core clean ups.

1. Starting in Log4j 2.1, you can specify a custom ShutdownCallbackRegistry to override the

default JVM shutdown hook strategy.

2. Starting in Log4j 2.6, you can now use

org.apache.logging.log4j.LogManager.shutdown() to initiate shutdown

manually.

7. Calls to org.apache.log4j.Logger.setLevel() or similar methods

are not supported in the API. Applications should remove these. Equivalent

functionality is provided in the Log4j 2 implementation classes, see

org.apache.logging.log4j.core.config.Configurator.setLevel(), but may leave

the application susceptible to changes in Log4j 2 internals.

8. Where appropriate, applications should convert to use parameterized messages instead of String

concatenation.

3 Log4j 1.x Migration 11

9. org.apache.log4j.MDC and org.apache.log4j.NDC have been replaced by the Thread

Context.

3.1.3 Configuring Log4j 2

Although the Log4j 2 configuration syntax is different than that of Log4j 1.x, most, if not all, of the

same functionality is available.

Note that system property interpolation via the ${foo} syntax has been extended to allow property

lookups from many different sources. See the Lookups documentation for more details. For example,

using a lookup for the system property named catalina.base, in Log4j 1.x, the syntax would be

${catalina.base}. In Log4j 2, the syntax would be ${sys:catalina.base}.

Log4j 1.x has a XMLLayout which is different from the XmlLayout in Log4j 2, the log4j-1.2-api

module contains a Log4j1XmlLayout which produce output in the format as in Log4j 1.x. The

Log4j 1.x SimpleLayout can be emulated with PatternLayout "%level - %m%n". The Log4j 1.x

TTCCLayout can be emulated with PatternLayout "%r [%t] %p %c %notEmpty{%ndc }- %m%n".

Both PatternLayout and EnhancedPatternLayout in Log4j 1.x can be replaced with

PatternLayout in Log4j 2. The log4j-1.2-api module contains two pattern conversions "%ndc" and

"%properties" which can be used to emulate "%x" and "%X" in Log4j 1.x PatternLayout ("%x" and

%X" in Log4j 2 have a slightly different format).

Below are the example configurations for Log4j 1.x and their counterparts in Log4j 2.

3.1.3.1 Sample 1 - Simple configuration using a Console Appender

Log4j 1.x XML configuration

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE log4j:configuration PUBLIC "-//APACHE//DTD LOG4J 1.2//EN" "log4j.dtd">

<log4j:configuration xmlns:log4j='http://jakarta.apache.org/log4j/'>

</layout>

</appender>

</category>

<Root>

<appender-ref ref="STDOUT" />

</Root>

</log4j:configuration>

Log4j 2 XML configuration

3 Log4j 1.x Migration 12

<?xml version="1.0" encoding="UTF-8"?>

</Console>

</Appenders>

</Root>

</Loggers>

</Configuration>

3.1.3.2 Sample 2 - Simple configuration using a File Appender, XMLLayout and SimpleLayout

Log4j 1.x XML configuration

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE log4j:configuration PUBLIC "-//APACHE//DTD LOG4J 1.2//EN" "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">

</appender>

</appender>

<appender-ref ref="A1" />

</category>

<root>

<appender-ref ref="STDOUT" />

</Root>

</log4j:configuration>

Log4j 2 XML configuration

3 Log4j 1.x Migration 13

<?xml version="1.0" encoding="UTF-8"?>

</File>

</Console>

</Appenders>

</Logger>

</Root>

</Loggers>

</Configuration>

3.1.3.3 Sample 3 - SocketAppender

Log4j 1.x XML configuration. This example from Log4j 1.x is misleading. The SocketAppender does

not actually use a Layout. Configuring one will have no effect.

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE log4j:configuration PUBLIC "-//APACHE//DTD LOG4J 1.2//EN" "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">

</layout>

</appender>

</layout>

</appender>

<appender-ref ref="A1"/>

</category>

<root>

<appender-ref ref="STDOUT"/>

</Root>

</log4j:configuration>

Log4j 2 XML configuration

3 Log4j 1.x Migration 14

<?xml version="1.0" encoding="UTF-8"?>

</Socket>

</Console>

</Appenders>

</Logger>

</Root>

</Loggers>

</Configuration>

3.1.3.4 Sample 4 - AsyncAppender and TTCCLayout

Log4j 1.x XML configuration using the AsyncAppender.

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE log4j:configuration PUBLIC "-//APACHE//DTD LOG4J 1.2//EN" "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/" configDebug="true">

<appender-ref ref="TEMP"/>

</appender>

</layout>

</appender>

<root>

<appender-ref ref="ASYNC"/>

</Root>

</log4j:configuration>

Log4j 2 XML configuration.

3 Log4j 1.x Migration 15

<?xml version="1.0" encoding="UTF-8"?>

</File>

</Async>

</Appenders>

</Root>

</Loggers>

</Configuration>

3.1.3.5 Sample 5 - AsyncAppender with Console and File

Log4j 1.x XML configuration using the AsyncAppender.

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE log4j:configuration PUBLIC "-//APACHE//DTD LOG4J 1.2//EN" "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/" configDebug="true">

<appender-ref ref="TEMP"/>

<appender-ref ref="CONSOLE"/>

</appender>

</layout>

</appender>

</layout>

</appender>

<root>

<appender-ref ref="ASYNC"/>

</Root>

</log4j:configuration>

Log4j 2 XML configuration. Note that the Async Appender should be configured after the appenders

it references. This will allow it to shutdown properly.

3 Log4j 1.x Migration 16

<?xml version="1.0" encoding="UTF-8"?>

</Console>

</File>

</Async>

</Appenders>

</Root>

</Loggers>

</Configuration>

4 A P I 17

4 API

.......................................................................................................................................

4.1 Log4j 2 API

4.1.1 Overview

The Log4j 2 API provides the interface that applications should code to and provides the adapter

components required for implementers to create a logging implementation. Although Log4j 2 is

broken up between an API and an implementation, the primary purpose of doing so was not to allow

multiple implementations, although that is certainly possible, but to clearly define what classes and

methods are safe to use in "normal" application code.

4.1.1.1 Hello World!

No introduction would be complete without the customary Hello, World example. Here is ours. First,

a Logger with the name "HelloWorld" is obtained from the LogManager. Next, the logger is used

to write the "Hello, World!" message, however the message will be written only if the Logger is

configured to allow informational messages.

import org.apache.logging.log4j.LogManager;

import org.apache.logging.log4j.Logger;

public class HelloWorld {

private static final Logger logger = LogManager.getLogger("HelloWorld");

public static void main(String[] args) {

logger.info("Hello, World!");

}

The output from the call to logger.info() will vary significantly depending on the configuration used.

See the Configuration section for more details.

4.1.1.2 Substituting Parameters

Frequently the purpose of logging is to provide information about what is happening in the system,

which requires including information about the objects being manipulated. In Log4j 1.x this could be

accomplished by doing:

if (logger.isDebugEnabled()) {

logger.debug("Logging in user " + user.getName() + " with birthday " + user.getBirthdayCalendar());

}

Doing this repeatedly has the effect of making the code feel like it is more about logging than the

actual task at hand. In addition, it results in the logging level being checked twice; once on the call to

isDebugEnabled and once on the debug method. A better alternative would be:

logger.debug("Logging in user {} with birthday {}", user.getName(), user.getBirthdayCalendar());

With the code above the logging level will only be checked once and the String construction will only

occur when debug logging is enabled.

4.1.1.3 Formatting Parameters

Formatter Loggers leave formatting up to you if toString() is not what you want. To facilitate

formatting, you can use the same format strings as Java's Formatter. For example:

4 A P I 18

public static Logger logger = LogManager.getFormatterLogger("Foo");

logger.debug("Logging in user %s with birthday %s", user.getName(), user.getBirthdayCalendar());

logger.debug("Logging in user %1$s with birthday %2$tm %2$te,%2$tY", user.getName(), user.getBirthdayCalendar());

logger.debug("Integer.MAX_VALUE = %,d", Integer.MAX_VALUE);

logger.debug("Long.MAX_VALUE = %,d", Long.MAX_VALUE);

To use a formatter Logger, you must call one of the LogManager getFormatterLogger methods. The

output for this example shows that Calendar toString() is verbose compared to custom formatting:

2012-12-12 11:56:19,633 [main] DEBUG: User John Smith with birthday java.util.GregorianCalendar[time=?,areFieldsSet=false,areAllFieldsSet=false,lenient=true,zone=sun.util.calendar.ZoneInfo[id="America/New_York",offset=-18000000,dstSavings=3600000,useDaylight=true,transitions=235,lastRule=java.util.SimpleTimeZone[id=America/New_York,offset=-18000000,dstSavings=3600000,useDaylight=true,startYear=0,startMode=3,startMonth=2,startDay=8,startDayOfWeek=1,startTime=7200000,startTimeMode=0,endMode=3,endMonth=10,endDay=1,endDayOfWeek=1,endTime=7200000,endTimeMode=0]],firstDayOfWeek=1,minimalDaysInFirstWeek=1,ERA=?,YEAR=1995,MONTH=4,WEEK_OF_YEAR=?,WEEK_OF_MONTH=?,DAY_OF_MONTH=23,DAY_OF_YEAR=?,DAY_OF_WEEK=?,DAY_OF_WEEK_IN_MONTH=?,AM_PM=0,HOUR=0,HOUR_OF_DAY=0,MINUTE=0,SECOND=0,MILLISECOND=?,ZONE_OFFSET=?,DST_OFFSET=?]

2012-12-12 11:56:19,643 [main] DEBUG: User John Smith with birthday 05 23, 1995

2012-12-12 11:56:19,643 [main] DEBUG: Integer.MAX_VALUE = 2,147,483,647

2012-12-12 11:56:19,643 [main] DEBUG: Long.MAX_VALUE = 9,223,372,036,854,775,807

4.1.1.4 Mixing Loggers with Formatter Loggers

Formatter loggers give fine-grained control over the output format, but have the drawback that the

correct type must be specified (for example, passing anything other than a decimal integer for a %d

format parameter gives an exception).

If your main usage is to use {}-style parameters, but occasionally you need fine-grained control over

the output format, you can use the printf method:

public static Logger logger = LogManager.getLogger("Foo");

logger.debug("Opening connection to {}...", someDataSource);

logger.printf(Level.INFO, "Logging in user %1$s with birthday %2$tm %2$te,%2$tY", user.getName(), user.getBirthdayCalendar());

4.1.1.5 Java 8 lambda support for lazy logging

In release 2.4, the Logger interface added support for lambda expressions. This allows client code

to lazily log messages without explicitly checking if the requested log level is enabled. For example,

previously you would write:

// pre-Java 8 style optimization: explicitly check the log level

// to make sure the expensiveOperation() method is only called if necessary

if (logger.isTraceEnabled()) {

logger.trace("Some long-running operation returned {}", expensiveOperation());

}

With Java 8 you can achieve the same effect with a lambda expression. You no longer need to

explicitly check the log level:

// Java-8 style optimization: no need to explicitly check the log level:

// the lambda expression is not evaluated if the TRACE level is not enabled

logger.trace("Some long-running operation returned {}", () -> expensiveOperation());

4.1.1.6 Logger Names

Most logging implementations use a hierarchical scheme for matching logger names with logging

configuration. In this scheme, the logger name hierarchy is represented by '.' characters in

the logger name, in a fashion very similar to the hierarchy used for Java package names. For

example, org.apache.logging.appender and org.apache.logging.filter both have

org.apache.logging as their parent. In most cases, applications name their loggers by passing the

4 A P I 19

current class's name to LogManager.getLogger(...). Because this usage is so common, Log4j 2

provides that as the default when the logger name parameter is either omitted or is null. For example,

in all examples below the Logger will have a name of "org.apache.test.MyTest".

package org.apache.test;

public class MyTest {

private static final Logger logger = LogManager.getLogger(MyTest.class);

}

package org.apache.test;

public class MyTest {

private static final Logger logger = LogManager.getLogger(MyTest.class.getName());

}

package org.apache.test;

public class MyTest {

private static final Logger logger = LogManager.getLogger();

}

5 Configuration 20

5 Configuration

.......................................................................................................................................

5.1 Configuration

Inserting log requests into the application code requires a fair amount of planning and effort.

Observation shows that approximately 4 percent of code is dedicated to logging. Consequently, even

moderately sized applications will have thousands of logging statements embedded within their code.

Given their number, it becomes imperative to manage these log statements without the need to modify

them manually.

Configuration of Log4j 2 can be accomplished in 1 of 4 ways:

1. Through a configuration file written in XML, JSON, YAML, or properties format.

2. Programmatically, by creating a ConfigurationFactory and Configuration implementation.

3. Programmatically, by calling the APIs exposed in the Configuration interface to add components

to the default configuration.

4. Programmatically, by calling methods on the internal Logger class.

This page focuses primarily on configuring Log4j through a configuration file. Information on

programmatically configuring Log4j can be found at Extending Log4j 2 and Programmatic Log4j

Configuration.

Note that unlike Log4j 1.x, the public Log4j 2 API does not expose methods to add, modify or remove

appenders and filters or manipulate the configuration in any way.

5.1.1 Automatic Configuration

Log4j has the ability to automatically configure itself during initialization. When Log4j starts it

will locate all the ConfigurationFactory plugins and arrange them in weighted order from highest to

lowest. As delivered, Log4j contains four ConfigurationFactory implementations: one for JSON, one

for YAML, one for properties, and one for XML.

1. Log4j will inspect the "log4j.configurationFile" system property and, if set, will attempt

to load the configuration using the ConfigurationFactory that matches the file extension.

2. If no system property is set the properties ConfigurationFactory will look for log4j2-

test.properties in the classpath.

3. If no such file is found the YAML ConfigurationFactory will look for log4j2-test.yaml or

log4j2-test.yml in the classpath.

4. If no such file is found the JSON ConfigurationFactory will look for log4j2-test.json or

log4j2-test.jsn in the classpath.

5. If no such file is found the XML ConfigurationFactory will look for log4j2-test.xml in the

classpath.

6. If a test file cannot be located the properties ConfigurationFactory will look for

log4j2.properties on the classpath.

7. If a properties file cannot be located the YAML ConfigurationFactory will look for

log4j2.yaml or log4j2.yml on the classpath.

8. If a YAML file cannot be located the JSON ConfigurationFactory will look for log4j2.json or

log4j2.jsn on the classpath.

9. If a JSON file cannot be located the XML ConfigurationFactory will try to locate log4j2.xml

on the classpath.

10.If no configuration file could be located the DefaultConfiguration will be used. This will

cause logging output to go to the console.

5 Configuration 21

An example application named MyApp that uses log4j can be used to illustrate how this is done.

import com.foo.Bar;

// Import log4j classes.

import org.apache.logging.log4j.Logger;

import org.apache.logging.log4j.LogManager;

public class MyApp {

// Define a static logger variable so that it references the

// Logger instance named "MyApp".

private static final Logger logger = LogManager.getLogger(MyApp.class);

public static void main(final String... args) {

// Set up a simple configuration that logs on the console.

logger.trace("Entering application.");

Bar bar = new Bar();

if (!bar.doIt()) {

logger.error("Didn't do it.");

}

logger.trace("Exiting application.");

}

MyApp begins by importing log4j related classes. It then defines a static logger variable with the name

MyApp which happens to be the fully qualified name of the class.

MyApp uses the Bar class defined in the package com.foo.

package com.foo;

import org.apache.logging.log4j.Logger;

import org.apache.logging.log4j.LogManager;

public class Bar {

static final Logger logger = LogManager.getLogger(Bar.class.getName());

public boolean doIt() {

logger.entry();

logger.error("Did it again!");

return logger.exit(false);

}

Log4j will provide a default configuration if it cannot locate a configuration file. The default

configuration, provided in the DefaultConfiguration class, will set up:

• A ConsoleAppender attached to the root logger.

• A PatternLayout set to the pattern "%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg

%n" attached to the ConsoleAppender

Note that by default Log4j assigns the root logger to Level.ERROR.

5 Configuration 22

The output of MyApp would be similar to:

17:13:01.540 [main] ERROR com.foo.Bar - Did it again!

17:13:01.540 [main] ERROR MyApp - Didn't do it.

As was described previously, Log4j will first attempt to configure itself from configuration files. A

configuration equivalent to the default would look like:

<?xml version="1.0" encoding="UTF-8"?>

</Console>

</Appenders>

</Root>

</Loggers>

</Configuration>

Once the file above is placed into the classpath as log4j2.xml you will get results identical to those

listed above. Changing the root level to trace will result in results similar to:

17:13:01.540 [main] TRACE MyApp - Entering application.

17:13:01.540 [main] TRACE com.foo.Bar - entry

17:13:01.540 [main] ERROR com.foo.Bar - Did it again!

17:13:01.540 [main] TRACE com.foo.Bar - exit with (false)

17:13:01.540 [main] ERROR MyApp - Didn't do it.

17:13:01.540 [main] TRACE MyApp - Exiting application.

Note that status logging is disabled when the default configuration is used.

5.1.2 Additivity

Perhaps it is desired to eliminate all the TRACE output from everything except com.foo.Bar.

Simply changing the log level would not accomplish the task. Instead, the solution is to add a new

logger definition to the configuration:

</Root>

With this configuration all log events from com.foo.Bar will be recorded while only error events

will be recorded from all other components.

5 Configuration 23

In the previous example all the events from com.foo.Bar were still written to the Console. This is

because the logger for com.foo.Bar did not have any appenders configured while its parent did. In

fact, the following configuration

<?xml version="1.0" encoding="UTF-8"?>

</Console>

</Appenders>

</Logger>

</Root>

</Loggers>

</Configuration>

would result in

17:13:01.540 [main] TRACE com.foo.Bar - entry

17:13:01.540 [main] ERROR com.foo.Bar - Did it again!

17:13:01.540 [main] TRACE com.foo.Bar - exit (false)

17:13:01.540 [main] ERROR MyApp - Didn't do it.

Notice that the trace messages from com.foo.Bar appear twice. This is because the appender

associated with logger com.foo.Bar is first used, which writes the first instance to the Console.

Next, the parent of com.foo.Bar, which in this case is the root logger, is referenced. The event is

then passed to its appender, which is also writes to the Console, resulting in the second instance. This

is known as additivity. While additivity can be quite a convenient feature (as in the first previous

example where no appender reference needed to be configured), in many cases this behavior is

considered undesirable and so it is possible to disable it by setting the additivity attribute on the logger

to false:

5 Configuration 24

<?xml version="1.0" encoding="UTF-8"?>

</Console>

</Appenders>

</Logger>

</Root>

</Loggers>

</Configuration>

Once an event reaches a logger with its additivity set to false the event will not be passed to any of its

parent loggers, regardless of their additivity setting.

5.1.3 Automatic Reconfiguration

When configured from a File, Log4j has the ability to automatically detect changes to the

configuration file and reconfigure itself. If the monitorInterval attribute is specified on the

configuration element and is set to a non-zero value then the file will be checked the next time a

log event is evaluated and/or logged and the monitorInterval has elapsed since the last check. The

example below shows how to configure the attribute so that the configuration file will be checked for

changes only after at least 30 seconds have elapsed. The minimum interval is 5 seconds.

<?xml version="1.0" encoding="UTF-8"?>

...

</Configuration>

5.1.4 Chainsaw can automatically process your log files (Advertising appender configurations)

Log4j provides the ability to 'advertise' appender configuration details for all file-based appenders

as well as socket-based appenders. For example, for file-based appenders, the file location and the

pattern layout in the file are included in the advertisement. Chainsaw and other external systems can

discover these advertisements and use that information to intelligently process the log file.

The mechanism by which an advertisement is exposed, as well as the advertisement format, is specific

to each Advertiser implementation. An external system which would like to work with a specific

Advertiser implementation must understand how to locate the advertised configuration as well as the

format of the advertisement. For example, a 'database' Advertiser may store configuration details in

a database table. An external system can read that database table in order to discover the file location

and the file format.

5 Configuration 25

Log4j provides one Advertiser implementation, a 'multicastdns' Advertiser, which advertises appender

configuration details via IP multicast using the http://jmdns.sourceforge.net library.

Chainsaw automatically discovers log4j's multicastdns-generated advertisements and displays

those discovered advertisements in Chainsaw's Zeroconf tab (if the jmdns library is in Chainsaw's

classpath). To begin parsing and tailing a log file provided in an advertisement, just double-click

the advertised entry in Chainsaw's Zeroconf tab. Currently, Chainsaw only supports FileAppender

advertisements.

To advertise an appender configuration:

• Add the JmDns library from http://jmdns.sourceforge.net to the application classpath

• Set the 'advertiser' attribute of the configuration element to 'multicastdns'

• Set the 'advertise' attribute on the appender element to 'true'

• If advertising a FileAppender-based configuration, set the 'advertiseURI' attribute on the

appender element to an appropriate URI

FileAppender-based configurations require an additional 'advertiseURI' attribute to be specified on

the appender. The 'advertiseURI' attribute provides Chainsaw with information on how the file can be

accessed. For example, the file may be remotely accessible to Chainsaw via ssh/sftp by specifying a

Commons VFS ( http://commons.apache.org/proper/commons-vfs/) sftp:// URI, an http:// URI may

be used if the file is accessible through a web server, or a file:// URI can be specified if accessing the

file from a locally-running instance of Chainsaw.

Here is an example advertisement-enabled appender configuration which can be used by a locally-

running Chainsaw to automatically tail the log file (notice the file:// advertiseURI):

Please note, you must add the JmDns library from http://jmdns.sourceforge.net to your

application classpath in order to advertise with the 'multicastdns' advertiser.

<?xml version="1.0" encoding="UTF-8"?>

...

</Configuration>

...

</File>

</Appenders>

5.1.5 Configuration Syntax

As of version 2.9, for security reasons, Log4j does not process DTD in XML files. If you want to split

the configuration in multiple files, use XInclude or Composite Configuration.

As the previous examples have shown as well as those to follow, Log4j allows you to easily redefine

logging behavior without needing to modify your application. It is possible to disable logging for

certain parts of the application, log only when specific criteria are met such as the action being

performed for a specific user, route output to Flume or a log reporting system, etc. Being able to do

this requires understanding the syntax of the configuration files.

The configuration element in the XML file accepts several attributes:

Attribute Name Description

5 Configuration 26

advertiser (Optional) The Advertiser plugin name which will

be used to advertise individual FileAppender or

SocketAppender configurations. The only Advertiser

plugin provided is 'multicastdns".

dest Either "err", which will send output to stderr, or a file

path or URL.

monitorInterval The minimum amount of time, in seconds, that must

elapse before the file configuration is checked for

changes.

name The name of the configuration.

packages A comma separated list of package names to

search for plugins. Plugins are only loaded once per

classloader so changing this value may not have any

effect upon reconfiguration.

schema Identifies the location for the classloader to located the

XML Schema to use to validate the configuration. Only

valid when strict is set to true. If not set no schema

validation will take place.

shutdownHook Specifies whether or not Log4j should automatically

shutdown when the JVM shuts down. The shutdown

hook is enabled by default but may be disabled by

setting this attribute to "disable"

shutdownTimeout Specifies how many milliseconds appenders and

background tasks will get to shutdown when the

JVM shuts down. Default is zero which mean

that each appender uses its default timeout, and

don't wait for background tasks. Not all appenders

will honor this, it is a hint and not an absolute

guarantee that the shutdown procedure will not

take longer. Setting this too low increase the risk

of losing outstanding log events not yet written to

the final destination. See LoggerContext.stop(long,

java.util.concurrent.TimeUnit). (Not used if

shutdownHook is set to "disable".)

status The level of internal Log4j events that should

be logged to the console. Valid values for this

attribute are "trace", "debug", "info", "warn",

"error" and "fatal". Log4j will log details about

initialization, rollover and other internal actions

to the status logger. Setting status="trace" is

one of the first tools available to you if you need

to troubleshoot log4j.

(Alternatively, setting system property

log4j2.debug will also print internal Log4j2

logging to the console, including internal logging

that took place before the configuration file was

found.)

strict Enables the use of the strict XML format. Not

supported in JSON configurations.

verbose Enables diagnostic information while loading plugins.

5 Configuration 27

Log4j can be configured using two XML flavors; concise and strict. The concise format makes

configuration very easy as the element names match the components they represent however it cannot

be validated with an XML schema. For example, the ConsoleAppender is configured by declaring an

XML element named Console under its parent appenders element. However, element and attribute

names are are not case sensitive. In addition, attributes can either be specified as an XML attribute or

as an XML element that has no attributes and has a text value. So

and

</PatternLayout>

are equivalent.

The file below represents the structure of an XML configuration, but note that the elements in italics

below represent the concise element names that would appear in their place.

<?xml version="1.0" encoding="UTF-8"?>;

<Property name="name1">value</property>

</Properties>

filter ... />

appender ... >

filter ... />

appender>

...

</Appenders>

filter ... />

</Logger>

...

</Root>

</Loggers>

</Configuration>

See the many examples on this page for sample appender, filter and logger declarations.

5.Strict XML

In addition to the concise XML format above, Log4j allows configurations to be specified in a

more "normal" XML manner that can be validated using an XML Schema. This is accomplished by

replacing the friendly element names above with their object type as shown below. For example,

5 Configuration 28

instead of the ConsoleAppender being configuerd using an element named Console it is instead

configured as an appender element with a type attribute containing "Console".

<?xml version="1.0" encoding="UTF-8"?>;

<Property name="name1">value</property>

</Properties>

</Appender>

...

</Appenders>

</Logger>

...

</Root>

</Loggers>

</Configuration>

Below is a sample configuration using the strict format.

5 Configuration 29

<?xml version="1.0" encoding="UTF-8"?>

<Configuration status="debug" strict="true" name="XMLConfigTest"

packages="org.apache.logging.log4j.test">

<Property name="filename">target/test.log</Property>

</Properties>

</Filters>

</Appender>

</Filters>

</Appender>

</Layout>

</Appender>

</Appenders>

</Filter>

</Logger>

</Logger>

</Root>

</Loggers>

</Configuration>

5 Configuration 30

5.1.5.2 Configuration with JSON

In addition to XML, Log4j can be configured using JSON. The JSON format is very similar to the

concise XML format. Each key represents the name of a plugin and the key/value pairs associated

with it are its attributes. Where a key contains more than a simple value it itself will be a subordinate

plugin. In the example below, ThresholdFilter, Console, and PatternLayout are all plugins while the

Console plugin will be assigned a value of STDOUT for its name attribute and the ThresholdFilter

will be assigned a level of debug.

{ "configuration": { "status": "error", "name": "RoutingTest",

"packages": "org.apache.logging.log4j.test",

"properties": {

"property": { "name": "filename",

"value" : "target/rolling1/rollingtest-$${sd:type}.log" }

"ThresholdFilter": { "level": "debug" },

"appenders": {

"Console": { "name": "STDOUT",

"PatternLayout": { "pattern": "%m%n" },

"ThresholdFilter": { "level": "debug" }

"Routing": { "name": "Routing",

"Routes": { "pattern": "$${sd:type}",

"Route": [

{

"RollingFile": {

"name": "Rolling-${sd:type}", "fileName": "${filename}",

"filePattern": "target/rolling1/test1-${sd:type}.%i.log.gz",

"PatternLayout": {"pattern": "%d %p %c{1.} [%t] %m%n"},

"SizeBasedTriggeringPolicy": { "size": "500" }

}

{ "AppenderRef": "STDOUT", "key": "Audit"}

]

}

"loggers": {

"logger": { "name": "EventLogger", "level": "info", "additivity": "false",

"AppenderRef": { "ref": "Routing" }},

"root": { "level": "error", "AppenderRef": { "ref": "STDOUT" }}

}

Note that in the RoutingAppender the Route element has been declared as an array. This is valid

because each array element will be a Route component. This won't work for elements such as

appenders and filters, where each element has a different name in the concise format. Appenders and

filters can be defined as array elements if each appender or filter declares an attribute named "type"

that contains the type of the appender. The following example illustrates this as well as how to declare

multiple loggers as an array.

5 Configuration 31

{ "configuration": { "status": "debug", "name": "RoutingTest",

"packages": "org.apache.logging.log4j.test",

"properties": {

"property": { "name": "filename",

"value" : "target/rolling1/rollingtest-$${sd:type}.log" }

"ThresholdFilter": { "level": "debug" },

"appenders": {

"appender": [

{ "type": "Console", "name": "STDOUT", "PatternLayout": { "pattern": "%m%n" }, "ThresholdFilter": { "level": "debug" }},

{ "type": "Routing", "name": "Routing",

"Routes": { "pattern": "$${sd:type}",

"Route": [

{

"RollingFile": {

"name": "Rolling-${sd:type}", "fileName": "${filename}",

"filePattern": "target/rolling1/test1-${sd:type}.%i.log.gz",

"PatternLayout": {"pattern": "%d %p %c{1.} [%t] %m%n"},

"SizeBasedTriggeringPolicy": { "size": "500" }

}

{ "AppenderRef": "STDOUT", "key": "Audit"}

]

}

]

"loggers": {

"logger": [

{ "name": "EventLogger", "level": "info", "additivity": "false",

"AppenderRef": { "ref": "Routing" }},

{ "name": "com.foo.bar", "level": "error", "additivity": "false",

"AppenderRef": { "ref": "STDOUT" }}

"root": { "level": "error", "AppenderRef": { "ref": "STDOUT" }}

}

Additional runtime dependencies are required for using JSON configuration files.

5.1.5.3 Configuration with YAML

Log4j also supports using YAML for configuration files. The structure follows the same pattern as

both the XML and YAML configuration formats. For example:

5 Configuration 32

Configuration:

status: warn

properties:

property:

value: target/test-yaml.log

thresholdFilter:

level: debug

appenders:

Console:

PatternLayout:

Pattern: "%m%n"

File:

fileName: ${filename}

PatternLayout:

Pattern: "%d %p %C{1.} [%t] %m%n"

Filters:

ThresholdFilter:

level: error

Loggers:

logger:

level: debug

additivity: false

ThreadContextMapFilter:

KeyValuePair:

key: test

value: 123

AppenderRef:

ref: STDOUT

level: debug

additivity: false

AppenderRef:

ref: File

Root:

level: error

AppenderRef:

ref: STDOUT

Additional runtime dependencies are required for using YAML configuration files.

5 Configuration 33

5.1.5.4 Configuring loggers

An understanding of how loggers work in Log4j is critical before trying to configure them. Please

reference the Log4j architecture if more information is required. Trying to configure Log4j without

understanding those concepts will lead to frustration.

A LoggerConfig is configured using the logger element. The logger element must have a name

attribute specified, will usually have a level attribute specified and may also have an additivity

attribute specified. The level may be configured with one of TRACE, DEBUG, INFO, WARN,

ERROR, ALL or OFF. If no level is specified it will default to ERROR. The additivity attribute may

be assigned a value of true or false. If the attribute is omitted the default value of true will be used.

A LoggerConfig (including the root LoggerConfig) can be configured with properties that will be

added to the properties copied from the ThreadContextMap. These properties can be referenced from

Appenders, Filters, Layouts, etc just as if they were part of the ThreadContext Map. The properties

can contain variables that will be resolved either when the configuration is parsed or dynamically

when each event is logged. See Property Substitution for more information on using variables.

The LoggerConfig may also be configured with one or more AppenderRef elements. Each appender

referenced will become associated with the specified LoggerConfig. If multiple appenders are

configured on the LoggerConfig each of them be called when processing logging events.

Every configuration must have a root logger. If one is not configured the default root LoggerConfig,

which has a level of ERROR and has a Console appender attached, will be used. The main differences

between the root logger and other loggers are

1. The root logger does not have a name attribute.

2. The root logger does not support the additivity attribute since it has no parent.

5.1.5.5 Configuring Appenders

An appender is configured either using the specific appender plugin's name or with an appender

element and the type attibute containing the appender plugin's name. In addition each appender must

have a name attribute specified with a value that is unique within the set of appenders. The name will

be used by loggers to reference the appender as described in the previous section.

Most appenders also support a layout to be configured (which again may be specified either using the

specific Layout plugin's name as the element or with "layout" as the element name along with a type

attribute that contains the layout plugin's name. The various appenders will contain other attributes or

elements that are required for them to function properly.

5.1.5.6 Configuring Filters

Log4j allows a filter to be specified in any of 4 places:

1. At the same level as the appenders, loggers and properties elements. These filters can accept or

reject events before they have been passed to a LoggerConfig.

2. In a logger element. These filters can accept or reject events for specific loggers.

3. In an appender element. These filters can prevent or cause events to be processed by the

appender.

4. In an appender reference element. These filters are used to determine if a Logger should route the

event to an appender.

Although only a single filter element can be configured, that element may be the filters element

which represents the CompositeFilter. The filters element allows any number of filter elements

to be configured within it. The following example shows how multiple filters can be configured on the

ConsoleAppender.

5 Configuration 34

<?xml version="1.0" encoding="UTF-8"?>

<Property name="filename">target/test.log</Property>

</Properties>

</Console>

</filters>

</Console>

</PatternLayout>

</File>

</Appenders>

</ThreadContextMapFilter>

</Logger>

</ThreadContextMapFilter>

</AppenderRef>

</Logger>

</Root>

</Loggers>

</Configuration>

5 Configuration 35

5.1.5.7 Configuration with Properties

As of version 2.4, Log4j now supports configuration via properties files. Note that the property syntax

is NOT the same as the syntax used in Log4j 1. Like the XML and JSON configurations, properties

configurations define the configuration in terms of plugins and attributes to the plugins.

Prior to version 2.6, the properties configuration requires that you list the identifiers of the

appenders, filters and loggers, in a comma separated list in properties with those names. Each

of those components will then be expected to be defined in sets of properties that begin with

component.<.identifier>.. The identifier does not have to match the name of the component

being defined but must uniquely identify all the attributes and subcomponents that are part of the

component. If the list of identifiers is not present the identier must not contain a '.'. Each individual

component MUST have a "type" attribute specified that identifies the component's Plugin type.

As of version 2.6, this list of identifiers is no longer required as names are inferred upon first usage,

however if you wish to use more complex identifies you must still use the list. If the list is present it

will be used.

Unlike the base components, when creating subcomponents you cannot specify an element containing

a list of identifiers. Instead, you must define the wrapper element with its type as is shown in the

policies definition in the rolling file appender below. You then define each of the subcomponents

below that wrapper element, as the TimeBasedTriggeringPolicy and SizeBasedTriggeringPolicy are

defined below.

Properties configuration files support the advertiser, monitorInterval, name, packages,

shutdownHook, shutdownTimeout, status, verbose, and dest attrbutes. See Configuration Syntax for

the definitions of these attributes.

5 Configuration 36

status = error

dest = err

name = PropertiesConfig

property.filename = target/rolling/rollingtest.log

filter.threshold.type = ThresholdFilter

filter.threshold.level = debug

appender.console.type = Console

appender.console.name = STDOUT

appender.console.layout.type = PatternLayout

appender.console.layout.pattern = %m%n

appender.console.filter.threshold.type = ThresholdFilter

appender.console.filter.threshold.level = error

appender.rolling.type = RollingFile

appender.rolling.name = RollingFile

appender.rolling.fileName = ${filename}

appender.rolling.filePattern = target/rolling2/test1-%d{MM-dd-yy-HH-mm-ss}-%i.log.gz

appender.rolling.layout.type = PatternLayout

appender.rolling.layout.pattern = %d %p %C{1.} [%t] %m%n

appender.rolling.policies.type = Policies

appender.rolling.policies.time.type = TimeBasedTriggeringPolicy

appender.rolling.policies.time.interval = 2

appender.rolling.policies.time.modulate = true

appender.rolling.policies.size.type = SizeBasedTriggeringPolicy

appender.rolling.policies.size.size=100MB

appender.rolling.strategy.type = DefaultRolloverStrategy

appender.rolling.strategy.max = 5

logger.rolling.name = com.example.my.app

logger.rolling.level = debug

logger.rolling.additivity = false

logger.rolling.appenderRef.rolling.ref = RollingFile

rootLogger.level = info

rootLogger.appenderRef.stdout.ref = STDOUT

5.1.6 Property Substitution

Log4j 2 supports the ability to specify tokens in the configuration as references to properties defined

elsewhere. Some of these properties will be resolved when the configuration file is interpreted while

others may be passed to components where they will be evaluated at runtime. To accomplish this,

Log4j uses variations of Apache Commons Lang's StrSubstitutor and StrLookup classes. In a

manner similar to Ant or Maven, this allows variables declared as ${name} to be resolved using

properties declared in the configuration itself. For example, the following example shows the filename

for the rolling file appender being declared as a property.

5 Configuration 37

<?xml version="1.0" encoding="UTF-8"?>

<Property name="filename">target/rolling1/rollingtest-$${sd:type}.log</Property>

</Properties>

</Console>

<Route>

<RollingFile name="Rolling-${sd:type}" fileName="${filename}"

filePattern="target/rolling1/test1-${sd:type}.%i.log.gz">

</PatternLayout>

</RollingFile>

</Route>

</Routes>

</Routing>

</Appenders>

</Logger>

</Root>

</Loggers>

</Configuration>

While this is useful, there are many more places properties can originate from. To accommodate this,

Log4j also supports the syntax ${prefix:name} where the prefix identifies tells Log4j that variable

name should be evaluated in a specific context. See the Lookups manual page for more details. The

contexts that are built in to Logj4 are:

Prefix Context

bundle Resource bundle. The format is

${bundle:BundleName:BundleKey}.

The bundle name follows package

naming conventions, for example:

${bundle:com.domain.Messages:MyKey}.

5 Configuration 38

ctx Thread Context Map (MDC)

date Inserts the current date and/or time using the specified

format

env System environment variables. The formats are

${env:ENV_NAME} and ${env:ENV_NAME:-

default_value}.

jndi A value set in the default JNDI Context.

jvmrunargs A JVM input argument accessed through

JMX, but not a main argument; see

RuntimeMXBean.getInputArguments(). Not available

on Android.

log4j Log4j configuration properties. The expressions

${log4j:configLocation} and

${log4j:configParentLocation}

respectively provide the absolute path to the log4j

configuration file and its parent folder.

main A value set with

MapLookup.setMainArguments(String[])

map A value from a MapMessage

sd A value from a StructuredDataMessage. The key "id"

will return the name of the StructuredDataId without

the enterprise number. The key "type" will return the

message type. Other keys will retrieve individual

elements from the Map.

sys System properties. The formats are

${sys:some.property} and

${sys:some.property:-default_value}.

A default property map can be declared in the configuration file. If the value cannot be located in

the specified lookup the value in the default property map will be used. The default map is pre-

populated with a value for "hostName" that is the current system's host name or IP address and the

"contextName" with is the value of the current logging context.

5.1.7 Lookup Variables with Multiple Leading '$' Characters

An interesting feature of StrLookup processing is that when a variable reference is declared with

multiple leading '$' characters each time the variable is resolved the leading '$' is simply removed. In

the previous example the "Routes" element is capable of resolving the variable at runtime. To allow

this the prefix value is specified as a variable with two leading '$' characters. When the configuration

file is first processed the first '$' character is simply removed. Thus, when the Routes element is

evaluated at runtime it is the variable declaration "${sd:type}" which causes the event to be inspected

for a StructuredDataMessage and if one is present the value of its type attribute to be used as the

routing key. Not all elements support resolving variables at runtime. Components that do will

specifically call that out in their documentation.

If no value is found for the key in the Lookup associated with the prefix then the value associated

with the key in the properties declaration in the configuration file will be used. If no value is found the

variable declaration will be returned as the value. Default values may be declared in the configuration

by doing:

5 Configuration 39

<?xml version="1.0" encoding="UTF-8"?>

<Property name="type">Audit</property>

</Properties>

...

</Configuration>

As a footnote, it is worth pointing out that the variables in the RollingFile appender declaration will

also not be evaluated when the configuration is processed. This is simply because the resolution

of the whole RollingFile element is deferred until a match occurs. See RoutingAppender for more

information.

5.1.8 Scripts

Log4j provides support for JSR 223 scripting languages to be used in some of its components.

Any language that provides support for the JSR 223 scripting engine may be used. A list of the

languages and bindings for them can be found at the Scripting Engine web site. However, some of

the languages listed there, such as JavaScript, Groovy and Beanshell, directly support the JSR 223

scripting framework and only require that the jars for that language be installed.

The components that support using scripts do so by allowing a <script>, <scriptFile>, or <scriptRef>

element to be configured on them. The script element contains a name for the script, the language

of the script, and the script text. The scriptFile element contains the name of the script, its location,

its language, its charset, and whether the file should be watched for changes. The scriptRef element

contains the name of the script that is defined in the <scripts> configuration element. The name of

the script is used to store the script, along with its ScriptEngine, so it can quickly be located each

time the script needs to be run. While the name is not required, providing it will help in debugging

problems when the script is running. The language must be provided on the script element and must

specify one of the language names that appear in the Configuration status log as described in the next

section. If the language is not specified on the scriptFile element the language will be determined by

the file extension of the script path. If file monitoring is requested it will only be enabled if a non-

zero monitorInterval is specified on the configuration element. That interval will be used to check for

changes in the file.

5 Configuration 40

<?xml version="1.0" encoding="UTF-8"?>

<Script name="selector" language="javascript"><![CDATA[

var result;

if (logEvent.getLoggerName().equals("JavascriptNoLocation")) {

result = "NoLocation";

} else if (logEvent.getMarker() != null && logEvent.getMarker().isInstanceOf("FLOW")) {

result = "Flow";

}

result;

]]></Script>

</Scripts>

</ScriptPatternSelector>

</Console>

</Appenders>

<Script name="GroovyFilter" language="groovy"><![CDATA[

if (logEvent.getMarker() != null && logEvent.getMarker().isInstanceOf("FLOW")) {

return true;

} else if (logEvent.getContextMap().containsKey("UserId")) {

return true;

}

return false;

]]>

</Script>

</ScriptFilter>

</Logger>

</ScriptFilter>

</Root>

</Loggers>

</Configuration>

5 Configuration 41

If the status attribute on the Configuration element is set to DEBUG the list of script engines currently

installed and their attributes will be listed. Although some engines may say they are not thread safe,

Log4j takes steps to insure that the scripts will run in a thread-safe manner if the engine advertises

that it is not thread safe.

2015-09-27 16:13:22,925 main DEBUG Installed script engines

2015-09-27 16:13:22,963 main DEBUG AppleScriptEngine Version: 1.1, Language: AppleScript, Threading: Not Thread Safe,

Compile: false, Names: {AppleScriptEngine, AppleScript, OSA}

2015-09-27 16:13:22,983 main DEBUG Groovy Scripting Engine Version: 2.0, Language: Groovy, Threading: MULTITHREADED,

Compile: true, Names: {groovy, Groovy}

2015-09-27 16:13:23,030 main DEBUG BeanShell Engine Version: 1.0, Language: BeanShell, Threading: MULTITHREADED,

Compile: true, Names: {beanshell, bsh, java}

2015-09-27 16:13:23,039 main DEBUG Mozilla Rhino Version: 1.7 release 3 PRERELEASE, Language: ECMAScript, Threading: MULTITHREADED,

Compile: true, Names: {js, rhino, JavaScript, javascript, ECMAScript, ecmascript}

When the scripts are executed they will be provided with a set of variables that should allow them

to accomplish whatever task they are expected to perform. See the documentation for the individual

components for the list of variables that are available to the script.

The components that support scripting expect a return value to be passed back to the calling Java

code. This is not a problem for several of the scripting languages, but Javascript does not allow a

return statement unless it is within a function. However, Javascript will return the value of the last

statement executed in the script. As a consequence, code such as that shown below will result in the

desired behavior.

var result;

if (logEvent.getLoggerName().equals("JavascriptNoLocation")) {

result = "NoLocation";

} else if (logEvent.getMarker() != null && logEvent.getMarker().isInstanceOf("FLOW")) {

result = "Flow";

}

result;

5.1.8.1 A special note on Beanshell

JSR 223 scripting engines are supposed to identify that they support the Compilable interface if they

support compiling their scripts. Beanshell does this. However, whenever the compile method is called

it throws an Error (not an Exception). Log4j catches this but will log the warning shown below for

each Beanshell script when it tries to compile them. All Beanshell scripts will then be interpreted on

each execution.

2015-09-27 16:13:23,095 main DEBUG Script BeanShellSelector is compilable

2015-09-27 16:13:23,096 main WARN Error compiling script java.lang.Error: unimplemented

at bsh.engine.BshScriptEngine.compile(BshScriptEngine.java:175)

at bsh.engine.BshScriptEngine.compile(BshScriptEngine.java:154)

at org.apache.logging.log4j.core.script.ScriptManager$MainScriptRunner.<init>(ScriptManager.java:125)

at org.apache.logging.log4j.core.script.ScriptManager.addScript(ScriptManager.java:94)

5 Configuration 42

5.1.9 XInclude

XML configuration files can include other files with XInclude. Here is an example log4j2.xml file

that includes two other files:

<?xml version="1.0" encoding="UTF-8"?>

<configuration xmlns:xi="http://www.w3.org/2001/XInclude"

status="warn" name="XIncludeDemo">

<property name="filename">xinclude-demo.log</property>

</properties>

<xi:include href="log4j-xinclude-appenders.xml" />

<xi:include href="log4j-xinclude-loggers.xml" />

</configuration>

log4j-xinclude-appenders.xml:

<?xml version="1.0" encoding="UTF-8"?>

</Console>

</PatternLayout>

</File>

</appenders>

log4j-xinclude-loggers.xml:

<?xml version="1.0" encoding="UTF-8"?>

</ThreadContextMapFilter>

</logger>

</logger>

</root>

</loggers>

5 Configuration 43

5.1.10 Composite Configuration

Log4j allows multiple configuration files to be used by specifying them as a list of comma separated

file paths on log4j.configurationFile. The merge logic can be controlled by specifying a class that

implements the MergeStrategy interface on the log4j.mergeStrategy property. The default merge

strategy will merge the files using the following rules:

1. The global configuration attributes are aggregated with those in later configurations replacing

those in previous configurations, with the exception that the highest status level and the lowest

monitorInterval greater than 0 will be used.

2. Properties from all configurations are aggregated. Duplicate properties replace those in previous

configurations.

3. Filters are aggregated under a CompositeFilter if more than one Filter is defined. Since Filters

are not named duplicates may be present.

4. Scripts and ScriptFile references are aggregated. Duplicate definiations replace those in previous

configurations.

5. Appenders are aggregated. Appenders with the same name are replaced by those in later

configurations, including all of the Appender's subcomponents.

6. Loggers are all aggregated. Logger attributes are individually merged with duplicates being

replaced by those in later configurations. Appender references on a Logger are aggregated with

duplicates being replaced by those in later configurations. Filters on a Logger are aggregated

under a CompositeFilter if more than one Filter is defined. Since Filters are not named duplicates

may be present. Filters under Appender references included or discarded depending on whether

their parent Appender reference is kept or discarded.

5.1.11 Status Messages

Troubleshooting tip for the impatient:

From log4j-2.9 onward, log4j2 will print all internal logging to the console if system property

log4j2.debug is defined (with any or no value).

Prior to log4j-2.9, there are two places where internal logging can be controlled:

• Before a configuration is found, status logger level can be controlled with system property

org.apache.logging.log4j.simplelog.StatusLogger.level.

• After a configuration is found, status logger level can be controlled in the configuration file with the "status"

attribute, for example: <Configuration status="trace">.

Just as it is desirable to be able to diagnose problems in applications, it is frequently necessary to

be able to diagnose problems in the logging configuration or in the configured components. Since

logging has not been configured, "normal" logging cannot be used during initialization. In addition,

normal logging within appenders could create infinite recursion which Log4j will detect and cause the

recursive events to be ignored. To accomodate this need, the Log4j 2 API includes a StatusLogger.

Components declare an instance of the StatusLogger similar to:

protected final static Logger logger = StatusLogger.getLogger();

Since StatusLogger implements the Log4j 2 API's Logger interface, all the normal Logger methods

may be used.

When configuring Log4j it is sometimes necessary to view the generated status events. This can

be accomplished by adding the status attribute to the configuration element or a default value can

be provided by setting the "Log4jDefaultStatusLevel" system property. Valid values of the status

5 Configuration 44

attribute are "trace", "debug", "info", "warn", "error" and "fatal". The following configuration has the

status attribute set to debug.

<?xml version="1.0" encoding="UTF-8"?>

<Property name="filename">target/rolling1/rollingtest-$${sd:type}.log</Property>

</Properties>

</Console>

<Route>

<RollingFile name="Rolling-${sd:type}" fileName="${filename}"

filePattern="target/rolling1/test1-${sd:type}.%i.log.gz">

</PatternLayout>

</RollingFile>

</Route>

</Routes>

</Routing>

</Appenders>

</Logger>

</Root>

</Loggers>

</Configuration>

During startup this configuration produces:

5 Configuration 45

2011-11-23 17:08:00,769 DEBUG Generated plugins in 0.003374000 seconds

2011-11-23 17:08:00,789 DEBUG Calling createProperty on class org.apache.logging.log4j.core.

config.Property for element property with params(name="filename",

value="target/rolling1/rollingtest-${sd:type}.log")

2011-11-23 17:08:00,792 DEBUG Calling configureSubstitutor on class org.apache.logging.log4j.

core.config.plugins.PropertiesPlugin for element properties with

params(properties={filename=target/rolling1/rollingtest-${sd:type}.log})

2011-11-23 17:08:00,794 DEBUG Generated plugins in 0.001362000 seconds

2011-11-23 17:08:00,797 DEBUG Calling createFilter on class org.apache.logging.log4j.core.

filter.ThresholdFilter for element ThresholdFilter with params(level="debug",

onMatch="null", onMismatch="null")

2011-11-23 17:08:00,800 DEBUG Calling createLayout on class org.apache.logging.log4j.core.

layout.PatternLayout for element PatternLayout with params(pattern="%m%n",

Configuration(RoutingTest), null, charset="null")

2011-11-23 17:08:00,802 DEBUG Generated plugins in 0.001349000 seconds

2011-11-23 17:08:00,804 DEBUG Calling createAppender on class org.apache.logging.log4j.core.

appender.ConsoleAppender for element Console with params(PatternLayout(%m%n), null,

target="null", name="STDOUT", ignoreExceptions="null")

2011-11-23 17:08:00,804 DEBUG Calling createFilter on class org.apache.logging.log4j.core.

filter.ThresholdFilter for element ThresholdFilter with params(level="debug",

onMatch="null", onMismatch="null")

2011-11-23 17:08:00,813 DEBUG Calling createRoute on class org.apache.logging.log4j.core.appender.

routing.Route for element Route with params(AppenderRef="null", key="null", Node=Route)

2011-11-23 17:08:00,823 DEBUG Calling createRoute on class org.apache.logging.log4j.core.appender.

routing.Route for element Route with params(AppenderRef="STDOUT", key="Audit", Node=Route)

2011-11-23 17:08:00,825 DEBUG Calling createRoutes on class org.apache.logging.log4j.core.appender.

routing.Routes for element Routes with params(pattern="${sd:type}",

routes={Route(type=dynamic default), Route(type=static Reference=STDOUT key='Audit'))})

2011-11-23 17:08:00,827 DEBUG Calling createAppender on class org.apache.logging.log4j.core.appender.

routing.RoutingAppender for element Routing with params(name="Routing",

ignoreExceptions="null", Routes({Route(type=dynamic default),Route(type=static

Reference=STDOUT key='Audit')}), Configuration(RoutingTest), null, null)

2011-11-23 17:08:00,827 DEBUG Calling createAppenders on class org.apache.logging.log4j.core.config.

plugins.AppendersPlugin for element appenders with params(appenders={STDOUT, Routing})

2011-11-23 17:08:00,828 DEBUG Calling createAppenderRef on class org.apache.logging.log4j.core.

config.plugins.AppenderRefPlugin for element AppenderRef with params(ref="Routing")

2011-11-23 17:08:00,829 DEBUG Calling createLogger on class org.apache.logging.log4j.core.config.

LoggerConfig for element logger with params(additivity="false", level="info", name="EventLogger",

AppenderRef={Routing}, null)

2011-11-23 17:08:00,830 DEBUG Calling createAppenderRef on class org.apache.logging.log4j.core.

config.plugins.AppenderRefPlugin for element AppenderRef with params(ref="STDOUT")

5 Configuration 46

2011-11-23 17:08:00,831 DEBUG Calling createLogger on class org.apache.logging.log4j.core.config.

LoggerConfig$RootLogger for element root with params(additivity="null", level="error",

AppenderRef={STDOUT}, null)

2011-11-23 17:08:00,833 DEBUG Calling createLoggers on class org.apache.logging.log4j.core.

config.plugins.LoggersPlugin for element loggers with params(loggers={EventLogger, root})

2011-11-23 17:08:00,834 DEBUG Reconfiguration completed

2011-11-23 17:08:00,846 DEBUG Calling createLayout on class org.apache.logging.log4j.core.

layout.PatternLayout for element PatternLayout with params(pattern="%d %p %c{1.} [%t] %m%n",

Configuration(RoutingTest), null, charset="null")

2011-11-23 17:08:00,849 DEBUG Calling createPolicy on class org.apache.logging.log4j.core.

appender.rolling.SizeBasedTriggeringPolicy for element SizeBasedTriggeringPolicy with

params(size="500")

2011-11-23 17:08:00,851 DEBUG Calling createAppender on class org.apache.logging.log4j.core.

appender.RollingFileAppender for element RollingFile with

params(fileName="target/rolling1/rollingtest-Unknown.log",

filePattern="target/rolling1/test1-Unknown.%i.log.gz", append="null", name="Rolling-Unknown",

bufferedIO="null", immediateFlush="null",

SizeBasedTriggeringPolicy(SizeBasedTriggeringPolicy(size=500)), null,

PatternLayout(%d %p %c{1.} [%t] %m%n), null, ignoreExceptions="null")

2011-11-23 17:08:00,858 DEBUG Generated plugins in 0.002014000 seconds

2011-11-23 17:08:00,889 DEBUG Reconfiguration started for context sun.misc.

Launcher$AppClassLoader@37b90b39

2011-11-23 17:08:00,890 DEBUG Generated plugins in 0.001355000 seconds

2011-11-23 17:08:00,959 DEBUG Generated plugins in 0.001239000 seconds

2011-11-23 17:08:00,961 DEBUG Generated plugins in 0.001197000 seconds

2011-11-23 17:08:00,965 WARN No Loggers were configured, using default

2011-11-23 17:08:00,976 DEBUG Reconfiguration completed

If the status attribute is set to error than only error messages will be written to the console. This makes

troubleshooting configuration errors possible. As an example, if the configuration above is changed to

have the status set to error and the logger declaration is:

</logger>

the following error message will be produced.

2011-11-24 23:21:25,517 ERROR Unable to locate appender Routng for logger EventLogger

Applications may wish to direct the status output to some other destination. This can be accomplished

by setting the dest attribute to either "err" to send the output to stderr or to a file location or URL. This

can also be done by insuring the configured status is set to OFF and then configuring the application

programmatically such as:

StatusConsoleListener listener = new StatusConsoleListener(Level.ERROR);

StatusLogger.getLogger().registerListener(listener);

5 Configuration 47

5.1.12 Testing in Maven

Maven can run unit and functional tests during the build cycle. By default, any files placed in src/

test/resources are automatically copied to target/test-classes and are included in the classpath

during execution of any tests. As such, placing a log4j2-test.xml into this directory will cause it to be

used instead of a log4j2.xml or log4j2.json that might be present. Thus a different log configuration

can be used during testing than what is used in production.

A second approach, which is extensively used by Log4j 2, is to set the log4j.configurationFile

property in the method annotated with @BeforeClass in the junit test class. This will allow an

arbitrarily named file to be used during the test.

A third approach, also used extensively by Log4j 2, is to use the LoggerContextRule JUnit test

rule which provides additional convenience methods for testing. This requires adding the log4j-

core test-jar dependency to your test scope dependencies. For example:

public class AwesomeTest {

@Rule

public LoggerContextRule init = new LoggerContextRule("MyTestConfig.xml");

@Test

public void testSomeAwesomeFeature() {

final LoggerContext ctx = init.getContext();

final Logger logger = init.getLogger("org.apache.logging.log4j.my.awesome.test.logger");

final Configuration cfg = init.getConfiguration();

final ListAppender app = init.getListAppender("List");

logger.warn("Test message");

final List<LogEvent> events = app.getEvents();

// etc.

}

5.1.13 System Properties

The Log4j documentation references a number of System Properties that can be used to control

various aspects of Log4j 2 behavior. The table below lists these properties along with their default

value and a description of what they control. Any spaces present in the property name are for visual

flow and should be removed.

Note that beginning in Log4j 2.10, all system property names have been normalized to follow

a consistent naming scheme. While the old property names are still supported for backwards

compatibility, it is recommended to update configurations to use the new style. This system is

extensible and is enabled through the PropertySource interface. Additional property source classes

can be added through the standard ServiceLoader mechanism in Java SE.

Properties can be overridden by sources with a lower number priority (e.g.., -100 comes before 100).

The following sources are all available by default:

Source Priority Description

5 Configuration 48

Environment Variables -100 Environment variables are all

prefixed with LOG4J_, are in all

caps, and words are all separated

by underscores. Only this naming

scheme is support for environment

variables as there were no old

naming schemes to maintain

compatibility with.

log4j2.component.properties

file 0 Including this file on the classpath

can be used as an alternative to

providing properties as system

properties. This has priority over

system properties, but they can

be overridden by environment

variables as described above.

System Properties 100 All properties can be set using

normal system property patterns.

These have the lowest priority and

can be overridden by included

properties files or environment

variables.

PropertySource priorities and descriptions

The following is a list of available global configuration properties. Note that these can only be set

once per JVM process unlike configuration settings available in configuration files. The Property

Name column contains the name used in properties files and system properties; Environemt Variable

for the equivalent environment variable; and Legacy Property Name for the pre-2.10 name.

* { // this works for all but td word-wrap:break-word; } table { // this somehow makes it work for td

table-layout:fixed; width:100%; }

Property Name

(Legacy Property

Name) Environment Variable Default Value Description

log4j2.configurationFile

( log4j.configurationFile) LOG4J_CONFIGURATION_FILE Path to an Log4j 2

configuration file.

May also contain a

comma separated list of

configuration file names.

log4j2.debug

( log4j2.debug) LOG4J_DEBUG Log4j2 will print all

internal logging to the

console if system property

log4j2.debug is

defined (with any or no

value).

log4j2.mergeFactory

( log4j.mergeFactory) LOG4J_MERGE_FACTORY The name of the

class that implements

the MergeStrategy

interface. If not specified

DefaultMergeStrategy

will be used

when creating a

CompositeConfiguration..

5 Configuration 49

log4j2.contextSelector

( Log4jContextSelector) LOG4J_CONTEXT_SELECTORClassLoaderContextSelectorCreates the

LoggerContexts.

An application can

have one or more

active LoggerContexts

depending on the

circumstances. See

Log Separation for more

details. Available context

selector implementation

classes:

org.apache.logging.log4j.core.async .AsyncLoggerContextSelector

- makes all loggers

asynchronous.

org.apache.logging.log4j.core.selector .BasicContextSelector

- creates a single shared

LoggerContext.

org.apache.logging.log4j.core.selector .ClassLoaderContextSelector

- separate

LoggerContexts for each

web application.

org.apache.logging.log4j.core.selector .JndiContextSelector

- use JNDI to locate

each web application's

LoggerContext.

org.apache.logging.log4j.core.osgi .BundleContextSelector

- separate

LoggerContexts for each

OSGi bundle.

log4j2.logEventFactory

( Log4jLogEventFactory) LOG4J_LOG_EVENT_FACTORYorg.apache.logging.log4j.core.impl .DefaultLogEventFactoryFactory class used by

LoggerConfig to create

LogEvent instances.

(Ignored when the

AsyncLoggerContextSelector

is used.)

log4j2.loggerContextFactory

(

log4j2.loggerContextFactory)

LOG4J_LOGGER_CONTEXT_FACTORYorg.apache.logging.log4j.simple .SimpleLoggerContextFactoryFactory class used

by LogManager to

bootstrap the logging

implementation. The

core jar provides

org.apache.logging.log4j.core .impl.Log4jContextFactory.

log4j2.configurationFactory

(

log4j.configurationFactory)

LOG4J_CONFIGURATION_FACTORY Fully specified class

name of a class extending

org.apache.logging.log4j.core .config.ConfigurationFactory.

If specified, an instance

of this class is added to

the list of configuration

factories.

5 Configuration 50

log4j2.shutdownHookEnabled

(

log4j.shutdownHookEnabled)

LOG4J_SHUTDOWN_HOOK_ENABLEDtrue Overrides the global

flag for whether or

not a shutdown hook

should be used to stop a

LoggerContext. By

default, this is enabled

and can be disabled on a

per-configuration basis.

When running with the

log4j-web module, this

is automatically disabled.

log4j2.shutdownCallbackRegistry

(

log4j.shutdownCallbackRegistry)

LOG4J_SHUTDOWN_CALLBACK_REGISTRYorg.apache.logging.log4j.core.util .DefaultShutdownCallbackRegistryFully specified class name

of a class implementing

ShutdownCallbackRegistry.

If specified, an

instance of this class

is used instead of

DefaultShutdownCallbackRegistry.

The specified class

must have a default

constructor.

log4j2.clock

( log4j.Clock) LOG4J_CLOCK SystemClock Implementation of the

org.apache.logging.log4j .core.util.Clock

interface that is used

for timestamping the log

events.

By default,

System.currentTimeMillis

is called on every log

event.

You can also specify a

fully qualified class name

of a custom class that

implements the Clock

interface.

log4j2.level

(

org.apache.logging.log4j.level)

LOG4J_LEVEL ERROR Log level of the default

configuration. The default

configuration is used if

the ConfigurationFactory

could not successfully

create a configuration

(e.g. no log4j2.xml file

was found).

log4j2.disableThreadContext

(disableThreadContext) LOG4J_DISABLE_THREAD_CONTEXTfalse If true, the

ThreadContext stack and

map are disabled. (May

be ignored if a custom

ThreadContext map is

specified.)

log4j2.disableThreadContextStack

(disableThreadContextStack)

LOG4J_DISABLE_THREAD_CONTEXT_STACKfalse If true, the

ThreadContext stack is

disabled.

5 Configuration 51

log4j2.disableThreadContextMap

(disableThreadContextMap)LOG4J_DISABLE_THREAD_CONTEXT_MAPfalse If true, the

ThreadContext map

is disabled. (May be

ignored if a custom

ThreadContext map is

specified.)

log4j2.threadContextMap

(log4j2.threadContextMap) LOG4J_THREAD_CONTEXT_MAP Fully specified class

name of a custom

ThreadContextMap

implementation class.

log4j2.isThreadContextMapInheritable

(isThreadContextMapInheritable)

LOG4J_IS_THREAD_CONTEXT_MAP_INHERITABLEfalse If true use a

InheritableThreadLocal

to implement the

ThreadContext map.

Otherwise, use a plain

ThreadLocal. (May

be ignored if a custom

ThreadContext map is

specified.)

log4j2.contextDataInjector

(

log4j2.ContextDataInjector)

LOG4J_CONTEXT_DATA_INJECTOR Fully specified class

name of a custom

ContextDataInjector

implementation class.

log4j2.garbagefreeThreadContextMap

(

log4j2.garbagefree.threadContextMap)

LOG4J_GARBAGEFREE_THREAD_CONTEXT_MAPfalse Specify "true" to make

the ThreadContext map

garbage-free.

log4j2.disableJmx

( log4j2.disable.jmx) LOG4J_DISABLE_JMX false If true, Log4j

configuration objects

like LoggerContexts,

Appenders, Loggers, etc.

will not be instrumented

with MBeans and cannot

be remotely monitored

and managed.

log4j2.jmxNotifyAsync

( log4j2.jmx.notify.async) LOG4J_JMX_NOTIFY_ASYNCfalse for web apps, true

otherwise If true, log4j's JMX

notifications are sent from

a separate background

thread, otherwise they

are sent from the caller

thread. If system property

log4j2.is.webapp

is true or the

javax.servlet.Servlet

class is on the classpath,

the default behaviour is

to use the caller thread to

send JMX notifications.

log4j2.skipJansi

( log4j.skipJansi) LOG4J_SKIP_JANSI true If true, the

ConsoleAppender will not

try to use the Jansi output

stream on Windows.

5 Configuration 52

log4j2.ignoreTCL

( log4j.ignoreTCL) LOG4J_IGNORE_TCL false If true, classes are only

loaded with the default

class loader. Otherwise,

an attempt is made to

load classes with the

current thread's context

class loader before falling

back to the default class

loader.

log4j2.uuidSequence

(

org.apache.logging.log4j.uuidSequence)

LOG4J_UUID_SEQUENCE 0 System property that may

be used to seed the UUID

generation with an integer

value.

log4j2.simplelogShowContextMap

(

org.apache.logging.log4j .simplelog.showContextMap)

LOG4J_SIMPLELOG_SHOW_CONTEXT_MAPfalse If true, the full

ThreadContext map

is included in each

SimpleLogger log

message.

log4j2.simplelogShowlogname

(

org.apache.logging.log4j .simplelog.showlogname)

LOG4J_SIMPLELOG_SHOWLOGNAMEfalse If true, the logger

name is included in

each SimpleLogger log

message.

log4j2.simplelogShowShortLogname

(

org.apache.logging.log4j .simplelog.showShortLogname)

LOG4J_SIMPLELOG_SHOW_SHORT_LOGNAMEtrue If true, only the last

component of a logger

name is included in

SimpleLogger log

messages. (E.g., if

the logger name is

"mycompany.myproject.mycomponent",

only "mycomponent" is

logged.

log4j2.simplelogShowdatetime

(

org.apache.logging.log4j .simplelog.showdatetime)

LOG4J_SIMPLELOG_SHOWDATETIMEfalse If true, SimpleLogger

log messages contain

timestamp information.

log4j2.simplelogDateTimeFormat

(

org.apache.logging.log4j .simplelog.dateTimeFormat)

LOG4J_SIMPLELOG_DATE_TIME_FORMAT"yyyy/MM/dd

HH:mm:ss:SSS zzz" Date-time format

to use. Ignored if

org.apache.logging.log4j .simplelog.showdatetime

is false.

log4j2.simplelogLogFile

(

org.apache.logging.log4j .simplelog.logFile)

LOG4J_SIMPLELOG_LOG_FILEsystem.err "system.err" (case-

insensitive) logs

to System.err,

"system.out" (case-

insensitive) logs to

System.out, any other

value is interpreted

as a file name to save

SimpleLogger messages

to.

log4j2.simplelogLevel

(

org.apache.logging.log4j .simplelog.level)

LOG4J_SIMPLELOG_LEVELERROR Default level for new

SimpleLogger instances.

log4j2.simplelog.<loggerName>.level

(

org.apache.logging.log4j .simplelog.<loggerName>.level)

LOG4J_SIMPLELOG_<LOGGER_NAME>_LEVELSimpleLogger default log

level Log level for a the

SimpleLogger instance

with the specified name.

5 Configuration 53

log4j2.simplelogStatusLoggerLevel

(

org.apache.logging.log4j.simplelog .StatusLogger.level)

LOG4J_SIMPLELOG_STATUS_LOGGER_LEVELERROR This property is used

to control the initial

StatusLogger level,

and can be overridden

in code by calling

StatusLogger.getLogger() .setLevel(someLevel).

Note that the

StatusLogger level is

only used to determine

the status log output

level until a listener is

registered. In practice,

a listener is registered

when a configuration

is found, and from that

point onwards, status

messages are only sent to

the listeners (depending

on their statusLevel).

log4j2.defaultStatusLevel

(

Log4jDefaultStatusLevel)

LOG4J_DEFAULT_STATUS_LEVELERROR The StatusLogger

logs events that

occur in the logging

system to the console.

During configuration,

AbstractConfiguration

registers a

StatusConsoleListener

with the StatusLogger

that may redirect

status log events from

the default console

output to a file. The

listener also supports

fine-grained filtering.

This system property

specifies the default

status log level for the

listener to use if the

configuration does not

specify a status level.

Note: this property is

used by the log4j-core

implementation only

after a configuration

file has been found.

5 Configuration 54

log4j2.statusLoggerLevel

(

log4j2.StatusLogger.level)

LOG4J_STATUS_LOGGER_LEVELWARN The initial

"listenersLevel" of

the StatusLogger.

If StatusLogger

listeners are added,

the "listenerLevel"

is changed to that

of the most verbose

listener. If any listeners

are registered, the

listenerLevel is used

to quickly determine

if an interested listener

exists.

By default,

StatusLogger listeners

are added when a

configuration is found

and by the JMX

StatusLoggerAdmin

MBean. For

example, if a

configuration contains

<Configuration

status="trace">,

a listener with

statusLevel TRACE

is registered and

the StatusLogger

listenerLevel is set

to TRACE, resulting

in verbose status

messages displayed on

the console.

If no listeners are

registered, the

listenersLevel is

not used, and the

StatusLogger output

level is determined by

StatusLogger.getLogger().getLevel()

(see property

org.apache.logging.log4j.simplelog .StatusLogger.level).

log4j2.statusEntries

( log4j2.status.entries) LOG4J_STATUS_ENTRIES200 Number of StatusLogger

events that are kept

in a buffer and can

be retrieved with

StatusLogger.getStatusData().

5 Configuration 55

log4j2.statusLoggerDateformat

(

log4j2.StatusLogger.DateFormat)

LOG4J_STATUS_LOGGER_DATEFORMAT Date-time format string

to use as the format

for timestamps in the

status logger output. See

java.text.SimpleDateFormat

for supported formats.

log4j2.asyncLoggerExceptionHandler

(

AsyncLogger.ExceptionHandler)

LOG4J_ASYNC_LOGGER_EXCEPTION_HANDLERdefault handler See Async Logger

System Properties for

details.

log4j2.asyncLoggerRingBufferSize

(

AsyncLogger.RingBufferSize)

LOG4J_ASYNC_LOGGER_RING_BUFFER_SIZE256 * 1024 See Async Logger

System Properties for

details.

log4j2.asyncLoggerWaitStrategy

(

AsyncLogger.WaitStrategy)

LOG4J_ASYNC_LOGGER_WAIT_STRATEGYTimeout See Async Logger

System Properties for

details.

log4j2.asyncLoggerThreadNameStrategy

(

AsyncLogger.ThreadNameStrategy)

LOG4J_ASYNC_LOGGER_THREAD_NAME_STRATEGYCACHED See Async Logger

System Properties for

details.

log4j2.asyncLoggerConfigExceptionHandler

(

AsyncLoggerConfig.ExceptionHandler)

LOG4J_ASYNC_LOGGER_CONFIG_EXCEPTION_HANDLERdefault handler See Mixed Async/

Synchronous Logger

System Properties for

details.

log4j2.asyncLoggerConfigRingBufferSize

(

AsyncLoggerConfig.RingBufferSize)

LOG4J_ASYNC_LOGGER_CONFIG_RING_BUFFER_SIZE256 * 1024 See Mixed Async/

Synchronous Logger

System Properties for

details.

log4j2.asyncLoggerConfigWaitStrategy

(

AsyncLoggerConfig.WaitStrategy)

LOG4J_ASYNC_LOGGER_CONFIG_WAIT_STRATEGYTimeout See Mixed Async/

Synchronous Logger

System Properties for

details.

log4j2.julLoggerAdapter

( log4j.jul.LoggerAdapter) LOG4J_JUL_LOGGER_ADAPTERorg.apache.logging.log4j .jul.ApiLoggerAdapterDefault LoggerAdapter to

use in the JUL adapter.

By default, if log4j-core is

available, then the class

org.apache.logging.log4j.jul .CoreLoggerAdapter

will be used.

Otherwise, the

ApiLogggerAdapter

will be used. Custom

implementations must

provide a public default

constructor.

log4j2.formatMsgAsync

( log4j.format.msg.async) LOG4J_FORMAT_MSG_ASYNCfalse If false (the default),

Log4j will make sure the

message is formatted

in the caller thread, to

ensure the value at the

time of the call to the

logger is the value that is

logged.

5 Configuration 56

log4j2.asyncQueueFullPolicy

(

log4j2.AsyncQueueFullPolicy)

LOG4J_ASYNC_QUEUE_FULL_POLICY Used by Async

Loggers and the

AsyncAppender to

maintain application

throughput even

when the underlying

appender cannot keep

up with the logging rate

and the queue is filling

up.

If no value is specified

(the default) events are

never discarded. If the

queue is full, the logger

call blocks until the

event can be added to

the queue.

Specify Discard to

drop events whose

level is equal or less

than the threshold level

(INFO by default)

when the queue is full.

log4j2.discardThreshold

(

log4j2.DiscardThreshold)

LOG4J_DISCARD_THRESHOLDINFO Used by the

DiscardingAsyncQueueFullPolicy

to determine which

events to drop when

the queue becomes

full. By default, INFO,

DEBUG and TRACE level

events are discarded

when the queue is full.

This property only has

effect if Discard

is specified as the

log4j2.AsyncQueueFullPolicy.

log4j2.messageFactory

( log4j2.messageFactory) LOG4J_MESSAGE_FACTORYorg.apache.logging.log4j.message.

ParameterizedMessageFactory

org.apache.logging.log4j.message.

ReusableMessageFactory

in garbage-free mode

Default message factory

used by Loggers if no

factory was specified.

log4j2.flowMessageFactory

(

log4j2.flowMessageFactory)

LOG4J_FLOW_MESSAGE_FACTORYorg.apache.logging.log4j.message.

DefaultFlowMessageFactoryDefault flow message

factory used by Loggers.

log4j2.isWebapp

( log4j2.is.webapp) LOG4J_IS_WEBAPP true if Servlet class on

class path This system property can

be used to force Log4j 2

to behave as if it is part of

a web application (when

true) or as if it is not part

of a web application

(when false).

5 Configuration 57

log4j2.enableThreadlocals

(

log4j2.enable.threadlocals)

LOG4J_ENABLE_THREADLOCALStrue This system property can

be used to switch off the

use of threadlocals, which

will partly disable Log4j's

garbage-free behaviour:

to be fully garbage-free,

Log4j stores objects in

ThreadLocal fields to

reuse them, otherwise

new objects are created

for each log event. Note

that this property is not

effective when Log4j

detects it is running in a

web application.

log4j2.enableDirectEncoders

(

log4j2.enable.direct.encoders)

LOG4J_ENABLE_DIRECT_ENCODERStrue This property can be

used to force garbage-

aware Layouts and

Appenders to revert to

the pre-2.6 behaviour

where converting log

events to text generates

temporary objects like

Strings and char[] arrays,

and converting this

text to bytes generates

temporary byte[] arrays.

By default, this property is

true and garbage-aware

Layouts and Appenders

that convert log events to

text will convert this text

to bytes without creating

temporary objects.

log4j2.initialReusableMsgSize

(

log4j.initialReusableMsgSize)

LOG4J_INITIAL_REUSABLE_MSG_SIZE128 In GC-free mode, this

property determines the

initial size of the reusable

StringBuilders where the

message text is formatted

and potentially passed to

background threads.

log4j2.maxReusableMsgSize

(

log4j.maxReusableMsgSize)

LOG4J_MAX_REUSABLE_MSG_SIZE518 In GC-free mode, this

property determines the

maximum size of the

reusable StringBuilders

where the message text is

formatted and potentially

passed to background

threads.

log4j2.layoutStringBuilderMaxSize

(

log4j.layoutStringBuilder.maxSize)

LOG4J_LAYOUT_STRING_BUILDER_MAX_SIZE2048 This property determines

the maximum size

of the thread-local

reusable StringBuilders

used to format the

log event to text by

Layouts that extend

AbstractStringLayout.

5 Configuration 58

log4j2.unboxRingbufferSize

(

log4j.unbox.ringbuffer.size)

LOG4J_UNBOX_RINGBUFFER_SIZE32 The

org.apache.logging.log4j.util.Unbox

utility manages a small

thread-local ring buffer

of StringBuilders. Each

time one of the box()

methods is called, the

next slot in the ring buffer

is used, until the ring

buffer is full and the first

slot is reused. By default

the Unbox ring buffer has

32 slots, so user code

can have up to 32 boxed

primitives in a single

logger call.

If more slots

are required, set

system property

log4j.unbox.ringbuffer.size

to the desired ring

buffer size. Note that

the specified number

will be rounded up to

the nearest power of 2.

log4j2.loggerContextStacktraceOnStart

(

log4j.LoggerContext.stacktrace.on.start)

LOG4J_LOGGER_CONTEXT_STACKTRACE_ON_STARTfalse Prints a stacktrace to

the status logger at

DEBUG level when the

LoggerContext is started.

For debug purposes.

log4j2.formatMsgNoLookups

(

log4j2.formatMsgNoLookups)

FORMAT_MESSAGES_PATTERN_DISABLE_LOOKUPSfalse Disables message pattern

lookups globally when

set to true. This is

equivalent to defining all

message patterns using

%m{nolookups}.

Log4j 2 global configuration properties

6 Web Applications and JSPs 59

6 Web Applications and JSPs

.......................................................................................................................................

6.1 Using Log4j 2 in Web Applications

You must take particular care when using Log4j or any other logging framework within a Java EE

web application. It's important for logging resources to be properly cleaned up (database connections

closed, files closed, etc.) when the container shuts down or the web application is undeployed.

Because of the nature of class loaders within web applications, Log4j resources cannot be cleaned up

through normal means. Log4j must be "started" when the web application deploys and "shut down"

when the web application undeploys. How this works varies depending on whether your application is

a Servlet 3.0 or newer or Servlet 2.5 web application.

In either case, you'll need to add the log4j-web module to your deployment as detailed in the

Maven, Ivy, and Gradle Artifacts manual page.

To avoid problems the Log4j shutdown hook will automatically be disabled when the log4j-web jar is

included.

6.1.1 Configuration

Log4j allows the configuration file to be specified in web.xml using the log4jConfiguration

context parameter. Log4j will search for configuration files by:

1. If a location is provided it will be searched for as a servlet context resource. For example, if

log4jConfiguration contains "logging.xml" then Log4j will look for a file with that name in

the root directory of the web application.

2. If no location is defined Log4j will search for a file that starts with "log4j2" in the WEB-INF

directory. If more than one file is found, and if a file that starts with "log4j2-name" is present,

where name is the name of the web application, then it will be used. Otherwise the first file will

be used.

3. The "normal" search sequence using the classpath and file URLs will be used to locate the

configuration file.

6.1.2 Servlet 3.0 and Newer Web Applications

A Servlet 3.0 or newer web application is any <web-app> whose version attribute has a value

of "3.0" or higher. Of course, the application must also be running in a compatible web container.

Some examples are: Tomcat 7.0 and higher, GlassFish 3.0 and higher, JBoss 7.0 and higher, Oracle

WebLogic 12c and higher, and IBM WebSphere 8.0 and higher.

6.1.2.1 The Short Story

Log4j 2 "just works" in Servlet 3.0 and newer web applications. It is capable of automatically

starting when the application deploys and shutting down when the application undeploys.

Thanks to the ServletContainerInitializer API added to Servlet 3.0, the relevant Filter and

ServletContextListener classes can be registered dynamically on web application startup.

Important Note! For performance reasons, containers often ignore certain JARs known not to

contain TLDs or ServletContainerInitializers and do not scan them for web-fragments and

initializers. Importantly, Tomcat 7 <7.0.43 ignores all JAR files named log4j*.jar, which prevents this

feature from working. This has been fixed in Tomcat 7.0.43, Tomcat 8, and later. In Tomcat 7 <7.0.43

you will need to change catalina.properties and remove "log4j*.jar" from the jarsToSkip

6 Web Applications and JSPs 60

property. You may need to do something similar on other containers if they skip scanning Log4j JAR

files.

6.1.2.2 The Long Story

The Log4j 2 Web JAR file is a web-fragment configured to order before any other web

fragments in your application. It contains a ServletContainerInitializer (

Log4jServletContainerInitializer) that the container automatically discovers and initializes. This adds

the Log4jServletContextListener and Log4jServletFilter to the ServletContext. These classes

properly initialize and deinitialize the Log4j configuration.

For some users, automatically starting Log4j is problematic or undesirable. You can easily disable

this feature using the isLog4jAutoInitializationDisabled context parameter. Simply add it

to your deployment descriptor with the value "true" to disable auto-initialization. You must define the

context parameter in web.xml. If you set in programmatically, it will be too late for Log4j to detect

the setting.

<context-param>

<param-name>isLog4jAutoInitializationDisabled</param-name>

<param-value>true</param-value>

</context-param>

Once you disable auto-initialization, you must initialize Log4j as you would a Servlet 2.5 web

application. You must do so in a way that this initialization happens before any other application code

(such as Spring Framework startup code) executes.

You can customize the behavior of the listener and filter using the log4jContextName,

log4jConfiguration, and/or isLog4jContextSelectorNamed context parameters. Read

more about this in the Context Parameters section below. You must not manually configure the

Log4jServletContextListener or Log4jServletFilter in your deployment descriptor (

web.xml) or in another initializer or listener in a Servlet 3.0 or newer application unless you disable

auto-initialization with isLog4jAutoInitializationDisabled. Doing so will result in startup

errors and unspecified erroneous behavior.

6.1.3 Servlet 2.5 Web Applications

A Servlet 2.5 web application is any <web-app> whose version attribute has a value of "2.5." The

version attribute is the only thing that matters; even if the web application is running in a Servlet

3.0 or newer container, it is a Servlet 2.5 web application if the version attribute is "2.5." Note that

Log4j 2 does not support Servlet 2.4 and older web applications.

If you are using Log4j in a Servlet 2.5 web application, or if you have disabled auto-initialization

with the isLog4jAutoInitializationDisabled context parameter, you must configure

the Log4jServletContextListener and Log4jServletFilter in the deployment descriptor or

programmatically. The filter should match all requests of any type. The listener should be the very

first listener defined in your application, and the filter should be the very first filter defined and

mapped in your application. This is easily accomplished using the following web.xml code:

6 Web Applications and JSPs 61

<listener-class>org.apache.logging.log4j.web.Log4jServletContextListener</listener-class>

</listener>

<filter-name>log4jServletFilter</filter-name>

<filter-class>org.apache.logging.log4j.web.Log4jServletFilter</filter-class>

</filter>

<filter-mapping>

<filter-name>log4jServletFilter</filter-name>

<url-pattern>/*</url-pattern>

<dispatcher>REQUEST</dispatcher>

<dispatcher>FORWARD</dispatcher>

<dispatcher>INCLUDE</dispatcher>

<dispatcher>ERROR</dispatcher>

<dispatcher>ASYNC</dispatcher>

</filter-mapping>

You can customize the behavior of the listener and filter using the log4jContextName,

log4jConfiguration, and/or isLog4jContextSelectorNamed context parameters. Read more

about this in the Context Parameters section below.

6.1.4 Context Parameters

By default, Log4j 2 uses the ServletContext's context name as the LoggerContext name

and uses the standard pattern for locating the Log4j configuration file. There are three context

parameters that you can use to control this behavior. The first, isLog4jContextSelectorNamed,

specifies whether the context should be selected using the JndiContextSelector. If

isLog4jContextSelectorNamed is not specified or is anything other than true, it is assumed to

be false.

If isLog4jContextSelectorNamed is true, log4jContextName must be specified or

display-name must be specified in web.xml; otherwise, the application will fail to start with an

exception. log4jConfiguration should also be specified in this case, and must be a valid URI for

the configuration file; however, this parameter is not required.

If isLog4jContextSelectorNamed is not true, log4jConfiguration may optionally be

specified and must be a valid URI or path to a configuration file or start with "classpath:" to denote

a configuration file that can be found on the classpath. Without this parameter, Log4j will use the

standard mechanisms for locating the configuration file.

When specifying these context parameters, you must specify them in the deployment descriptor (

web.xml) even in a Servlet 3.0 or never application. If you add them to the ServletContext within

a listener, Log4j will initialize before the context parameters are available and they will have no

effect. Here are some sample uses of these context parameters.

6.1.4.1 Set the Logging Context Name to "myApplication"

<context-param>

<param-name>log4jContextName</param-name>

<param-value>myApplication</param-value>

</context-param>

6 Web Applications and JSPs 62

6.1.4.2 Set the Configuration Path/File/URI to "/etc/myApp/myLogging.xml"

<context-param>

<param-name>log4jConfiguration</param-name>

<param-value>file:///etc/myApp/myLogging.xml</param-value>

</context-param>

6.1.4.3 Use the JndiContextSelector

<context-param>

<param-name>isLog4jContextSelectorNamed</param-name>

<param-value>true</param-value>

</context-param>

<context-param>

<param-name>log4jContextName</param-name>

<param-value>appWithJndiSelector</param-value>

</context-param>

<context-param>

<param-name>log4jConfiguration</param-name>

<param-value>file:///D:/conf/myLogging.xml</param-value>

</context-param>

Note that in this case you must also set the "Log4jContextSelector" system property to

"org.apache.logging.log4j.core.selector.JndiContextSelector".

6.1.5 Using Web Application Information During the Configuration

You may want to use information about the web application during configuration. For example,

you could embed the web application's context path in the name of a Rolling File Appender. See

WebLookup in Lookups for more information.

6.1.6 JavaServer Pages Logging

You may use Log4j 2 within JSPs just as you would within any other Java code. Simple obtain

a Logger and call its methods to log events. However, this requires you to use Java code within

your JSPs, and some development teams rightly are not comfortable with doing this. If you have a

dedicated user interface development team that is not familiar with using Java, you may even have

Java code disabled in your JSPs.

For this reason, Log4j 2 provides a JSP Tag Library that enables you to log events without using any

Java code. To read more about using this tag library, read the Log4j Tag Library documentation.

Important Note! As noted above, containers often ignore certain JARs known not to contain TLDs

and do not scan them for TLD files. Importantly, Tomcat 7 <7.0.43 ignores all JAR files named

log4j*.jar, which prevents the JSP tag library from being automatically discovered. This does not

affect Tomcat 6.x and has been fixed in Tomcat 7.0.43, Tomcat 8, and later. In Tomcat 7 <7.0.43

you will need to change catalina.properties and remove "log4j*.jar" from the jarsToSkip

property. You may need to do something similar on other containers if they skip scanning Log4j JAR

files.

6.1.7 Asynchronous Requests and Threads

6 Web Applications and JSPs 63

The handling of asynchronous requests is tricky, and regardless of Servlet container version or

configuration Log4j cannot handle everything automatically. When standard requests, forwards,

includes, and error resources are processed, the Log4jServletFilter binds the LoggerContext

to the thread handling the request. After request processing completes, the filter unbinds the

LoggerContext from the thread.

Similarly, when an internal request is dispatched using a javax.servlet.AsyncContext, the

Log4jServletFilter also binds the LoggerContext to the thread handling the request and

unbinds it when request processing completes. However, this only happens for requests dispatched

through the AsyncContext. There are other asynchronous activities that can take place other than

internal dispatched requests.

For example, after starting an AsyncContext you could start up a separate thread to process the

request in the background, possibly writing the response with the ServletOutputStream. Filters

cannot intercept the execution of this thread. Filters also cannot intercept threads that you start in the

background during non-asynchronous requests. This is true whether you use a brand new thread or a

thread borrowed from a thread pool. So what can you do for these special threads?

You may not need to do anything. If you didn't use the isLog4jContextSelectorNamed

context parameter, there is no need to bind the LoggerContext to the thread. Log4j can safely

locate the LoggerContext on its own. In these cases, the filter provides only very modest

performance gains, and only when creating new Loggers. However, if you did specify the

isLog4jContextSelectorNamed context parameter with the value "true", you will need to

manually bind the LoggerContext to asynchronous threads. Otherwise, Log4j will not be able to

locate it.

Thankfully, Log4j provides a simple mechanism for binding the LoggerContext to asynchronous

threads in these special circumstances. The simplest way to do this is to wrap the Runnable instance

that is passed to the AsyncContext.start() method.

6 Web Applications and JSPs 64

import java.io.IOException;

import javax.servlet.AsyncContext;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import org.apache.logging.log4j.LogManager;

import org.apache.logging.log4j.Logger;

import org.apache.logging.log4j.web.WebLoggerContextUtils;

public class TestAsyncServlet extends HttpServlet {

@Override

protected void doGet(final HttpServletRequest req, final HttpServletResponse resp) throws ServletException, IOException {

final AsyncContext asyncContext = req.startAsync();

asyncContext.start(WebLoggerContextUtils.wrapExecutionContext(this.getServletContext(), new Runnable() {

@Override

public void run() {

final Logger logger = LogManager.getLogger(TestAsyncServlet.class);

logger.info("Hello, servlet!");

}

}));

}

@Override

protected void doPost(final HttpServletRequest req, final HttpServletResponse resp) throws ServletException, IOException {

final AsyncContext asyncContext = req.startAsync();

asyncContext.start(new Runnable() {

@Override

public void run() {

final Log4jWebSupport webSupport =

WebLoggerContextUtils.getWebLifeCycle(TestAsyncServlet.this.getServletContext());

webSupport.setLoggerContext();

// do stuff

webSupport.clearLoggerContext();

}

});

}

This can be slightly more convenient when using Java 1.8 and lambda functions as demonstrated

below.

6 Web Applications and JSPs 65

import java.io.IOException;

import javax.servlet.AsyncContext;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import org.apache.logging.log4j.LogManager;

import org.apache.logging.log4j.Logger;

import org.apache.logging.log4j.web.WebLoggerContextUtils;

public class TestAsyncServlet extends HttpServlet {

@Override

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

final AsyncContext asyncContext = req.startAsync();

asyncContext.start(WebLoggerContextUtils.wrapExecutionContext(this.getServletContext(), () -> {

final Logger logger = LogManager.getLogger(TestAsyncServlet.class);

logger.info("Hello, servlet!");

}));

}

Alternatively, you can obtain the Log4jWebLifeCycle instance from the ServletContext

attributes, call its setLoggerContext method as the very first line of code in your asynchronous

thread, and call its clearLoggerContext method as the very last line of code in your asynchronous

thread. The following code demonstrates this. It uses the container thread pool to execute

asynchronous request processing, passing an anonymous inner Runnable to the start method.

6 Web Applications and JSPs 66

import java.io.IOException;

import javax.servlet.AsyncContext;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import org.apache.logging.log4j.LogManager;

import org.apache.logging.log4j.Logger;

import org.apache.logging.log4j.web.Log4jWebLifeCycle;

import org.apache.logging.log4j.web.WebLoggerContextUtils;

public class TestAsyncServlet extends HttpServlet {

@Override

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

final AsyncContext asyncContext = req.startAsync();

asyncContext.start(new Runnable() {

@Override

public void run() {

final Log4jWebLifeCycle webLifeCycle =

WebLoggerContextUtils.getWebLifeCycle(TestAsyncServlet.this.getServletContext());

webLifeCycle.setLoggerContext();

try {

final Logger logger = LogManager.getLogger(TestAsyncServlet.class);

logger.info("Hello, servlet!");

} finally {

webLifeCycle.clearLoggerContext();

}

});

}

Note that you must call clearLoggerContext once your thread is finished processing. Failing

to do so will result in memory leaks. If using a thread pool, it can even disrupt the logging of other

web applications in your container. For that reason, the example here shows clearing the context in a

finally block, which will always execute.

6.1.8 Using the Servlet Appender

Log4j provides a Servlet Appender that uses the servlet context as the log target. For example:

6 Web Applications and JSPs 67

</Servlet>

</Appenders>

</Root>

</Loggers>

</Configuration>

To avoid double logging of exceptions to the servlet context, you must use %ex{none} in your

PatternLayout as shown in the example. The exception will be omitted from the message text but

it is passed to the servlet context as the actual Throwable object.

7 Plugins 68

7 Plugins

.......................................................................................................................................

7.1 Plugins

7.1.1 Introduction

Log4j 1.x allowed for extension by requiring class attributes on most of the configuration

declarations. In the case of some elements, notably the PatternLayout, the only way to add new

pattern converters was to extend the PatternLayout class and add them via code. One goal of Log4j 2

is to make extending it extremely easy through the use of plugins.

In Log4j 2 a plugin is declared by adding a @Plugin annotation to the class declaration. During

initialization the Configuration will invoke the PluginManager to load the built-in Log4j plugins as

well as any custom plugins. The PluginManager locates plugins by looking in five places:

1. Serialized plugin listing files on the classpath. These files are generated automatically during the

build (more details below).

2. (OSGi only) Serialized plugin listing files in each active OSGi bundle. A BundleListener is

added on activation to continue checking new bundles after log4j-core has started.

3. A comma-separated list of packages specified by the log4j.plugin.packages system

property.

4. Packages passed to the static PluginManager.addPackages method (before Log4j

configuration occurs).

5. The packages declared in your log4j2 configuration file.

If multiple Plugins specify the same (case-insensitive) name, then the load order above determines

which one will be used. For example, to override the File plugin which is provided by the built-

in FileAppender class, you would need to place your plugin in a JAR file in the CLASSPATH

ahead of log4j-core.jar. This is not recommended; plugin name collisions will cause a warning

to be emitted. Note that in an OSGi environment, the order that bundles are scanned for plugins

generally follows the same order that bundles were installed into the framework. See getBundles()

and SynchronousBundleListener. In short, name collisions are even more unpredictable in an OSGi

environment.

Serialized plugin listing files are generated by an annotation processor contained in the log4j-

core artifact which will automatically scan your code for Log4j 2 plugins and output a metadata

file in your processed classes. There is nothing extra that needs to be done to enable this; the

Java compiler will automatically pick up the annotation processor on the class path unless you

explicitly disable it. In that case, it would be important to add another compiler pass to your build

process that only handles annotation processing using the Log4j 2 annotation processor class,

org.apache.logging.log4j.core.config.plugins.processor.PluginProcessor. To

do this using Apache Maven, add the following execution to your maven-compiler-plugin (version 2.2

or higher) build plugin:

7 Plugins 69

<groupId>org.apache.maven.plugins</groupId>

<artifactId>maven-compiler-plugin</artifactId>

<id>log4j-plugin-processor</id>

<goals>

<goal>compile</goal>

</goals>

<phase>process-classes</phase>

<annotationProcessor>org.apache.logging.log4j.core.config.plugins.processor.PluginProcessor</annotationProcessor>

</annotationProcessors>

</configuration>

</execution>

</executions>

</plugin>

As the configuration is processed the appropriate plugins will be automatically configured and

initialized. Log4j 2 utilizes a few different categories of plugins which are described in the following

sections.

7.1.2 Core

Core plugins are those that are directly represented by an element in a configuration file, such as an

Appender, Layout, Logger or Filter. Custom plugins that conform to the rules laid out in the next

paragraph may simply be referenced in the configuration, provided they are appropriate configured to

be loaded by the PluginManager.

Every Core plugin must declare a static method annotated with @PluginFactory or

@PluginBuilderFactory. The former is used for static factory methods that provide all options

as method parameters, and the latter is used to construct a new Builder<T> class whose fields

are used for injecting attributes and child nodes. To allow the Configuration to pass the correct

parameters to the method, every parameter to the method must be annotated as one of the following

attribute types. Each attribute or element annotation must include the name that must be present in the

configuration in order to match the configuration item to its respective parameter. For plugin builders,

the names of the fields will be used by default if no name is specified in the annotation. There are

dozens of plugins in Log4j Core that can be used as examples for more complex scenarios including

hierarchical builder classes (e.g., see FileAppender). See Extending Log4j with Plugin Builders for

more details.

7.1.2.1 Attribute Types

PluginAttribute

The parameter must be convertible from a String using a TypeConverter. Most built-in

types are already supported, but custom TypeConverter plugins may also be provided

for more type support. Note that PluginBuilderAttribute can be used in builder class

fields as an easier way to provide default values.

7 Plugins 70

PluginElement

The parameter may represent a complex object that itself has parameters that can be

configured. This also supports injecting an array of elements.

PluginConfiguration

The current Configuration object will be passed to the plugin as a parameter.

PluginNode

The current Node being parsed will be passed to the plugin as a parameter.

PluginValue

The value of the current Node or its attribute named value.

7.1.2.2 Constraint Validators

Plugin factory fields and parameters can be automatically validated at runtime using constraint

validators inspired by the Bean Validation spec. The following annotations are bundled in Log4j, but

custom ConstraintValidators can be created as well.

Required

This annotation validates that a value is non-empty. This covers a check for null as well as

several other scenarios: empty CharSequence objects, empty arrays, empty Collection

instances, and empty Map instances.

ValidHost

This annotation validates that a value corresponds to a valid hostname. This uses the same

validation as InetAddress::getByName.

ValidPort

This annotation validates that a value corresponds to a valid port number between 0 and

65535.

7.1.3 Converters

Converters are used by PatternLayout to render the elements identified by the conversion pattern.

Every converter must specify its category as "Converter" on the @Plugin annotation, have a static

newInstance method that accepts an array of Strings as its only parameter and returns an instance

of the Converter, and must have a @ConverterKeys annotation present that contains the array of

converter patterns that will cause the Converter to be selected. Converters that are meant to handle

LogEvents must extend the LogEventPatternConverter class and must implement a format method

that accepts a LogEvent and a StringBuilder as arguments. The Converter should append the

result of its operation to the StringBuilder.

A second type of Converter is the FileConverter - which must have "FileConverter" specified in the

category attribute of the @Plugin annotation. While similar to a LogEventPatternConverter,

instead of a single format method these Converters will have two variations; one that takes an Object

and one that takes an array of Objects instead of the LogEvent. Both append to the provided

StringBuilder in the same fashion as a LogEventPatternConverter. These Converters are

typically used by the RollingFileAppender to construct the name of the file to log to.

If multiple Converters specify the same ConverterKeys, then the load order above determines

which one will be used. For example, to override the %date converter which is provided by the

built-in DatePatternConverter class, you would need to place your plugin in a JAR file in

7 Plugins 71

the CLASSPATH ahead of log4j-core.jar. This is not recommended; pattern ConverterKeys

collisions will cause a warning to be emitted. Try to use unique ConverterKeys for your custom

pattern converters.

7.1.4 KeyProviders

Some components within Log4j may provide the ability to perform data encryption. These

components require a secret key to perform the encryption. Applications may provide the key by

creating a class that implements the SecretKeyProvider interface.

7.1.5 Lookups

Lookups are perhaps the simplest plugins of all. They must declare their type as "Lookup" on the

plugin annotation and must implement the StrLookup interface. They will have two methods; a

lookup method that accepts a String key and returns a String value and a second lookup method

that accepts both a LogEvent and a String key and returns a String. Lookups may be referenced by

specifying ${name:key} where name is the name specified in the Plugin annotation and key is the

name of the item to locate.

7.1.6 TypeConverters

TypeConverters are a sort of meta-plugin used for converting strings into other types in a plugin

factory method parameter. Other plugins can already be injected via the @PluginElement

annotation; now, any type supported by the type conversion system can be used in a

@PluginAttribute parameter. Conversion of enum types are supported on demand and do

not require custom TypeConverter classes. A large number of built-in Java classes are already

supported; see TypeConverters for a more exhaustive listing.

Unlike other plugins, the plugin name of a TypeConverter is purely cosmetic. Appropriate type

converters are looked up via the Type interface rather than via Class<?> objects only. Do note that

TypeConverter plugins must have a default constructor.

7.2 Developer Notes

If a plugin class implements Collection or Map, then no factory method is used. Instead, the class

is instantiated using the default constructor, and all child configuration nodes are added to the

Collection or Map.

8 Lookups 72

8 Lookups

.......................................................................................................................................

8.1 Lookups

Lookups provide a way to add values to the Log4j configuration at arbitrary places. They are a

particular type of Plugin that implements the StrLookup interface. Information on how to use

Lookups in configuration files can be found in the Property Substitution section of the Configuration

page.

8.1.1 Context Map Lookup

The ContextMapLookup allows applications to store data in the Log4j ThreadContext Map and then

retrieve the values in the Log4j configuration. In the example below, the application would store the

current user's login id in the ThreadContext Map with the key "loginId". During initial configuration

processing the first '$' will be removed. The PatternLayout supports interpolation with Lookups and

will then resolve the variable for each event. Note that the pattern "%X{loginId}" would achieve the

same result.

<pattern>%d %p %c{1.} [%t] $${ctx:loginId} %m%n</pattern>

</PatternLayout>

</File>

8.1.2 Date Lookup

The DateLookup is somewhat unusual from the other lookups as it doesn't use the key to locate an

item. Instead, the key can be used to specify a date format string that is valid for SimpleDateFormat.

The current date, or the date associated with the current log event will be formatted as specified.

</PatternLayout>

</RollingFile>

8.1.3 Environment Lookup

The EnvironmentLookup allows systems to configure environment variables, either in global files

such as /etc/profile or in the startup scripts for applications, and then retrieve those variables from

within the logging configuration. The example below includes the name of the currently logged in

user in the application log.

8 Lookups 73

</PatternLayout>

</File>

This lookup also supports default value syntax. In the sample below, when the USER environment

variable is undefined, the default value jdoe is used:

</PatternLayout>

</File>

8.1.4 Java Lookup

The JavaLookup allows Java environment information to be retrieved in convenient preformatted

strings using the java: prefix.

Key Description

version The short Java version, like:

Java version 1.7.0_67

runtime The Java runtime version, like:

Java(TM) SE Runtime Environment

(build 1.7.0_67-b01) from Oracle

Corporation

vm The Java VM version, like:

Java HotSpot(TM) 64-Bit Server VM

(build 24.65-b04, mixed mode)

os The OS version, like:

Windows 7 6.1 Service Pack 1,

architecture: amd64-64

locale Hardware information, like:

default locale: en_US, platform

encoding: Cp1252

hw Hardware information, like:

processors: 4, architecture:

amd64-64, instruction sets: amd64

For example:

8 Lookups 74

</PatternLayout>

</File>

8.1.5 Jndi Lookup

The JndiLookup allows variables to be retrieved via JNDI. By default the key will be prefixed with

java:comp/env/, however if the key contains a ":" no prefix will be added.

<pattern>%d %p %c{1.} [%t] $${jndi:logging/context-name} %m%n</pattern>

</PatternLayout>

</File>

Java's JNDI module is not available on Android.

8.1.6 JVM Input Arguments Lookup (JMX)

Maps JVM input arguments -- but not main arguments -- using JMX to acquire the JVM arguments.

Use the prefix jvmrunargs to access JVM arguments.

See the Javadocs for java.lang.management.RuntimeMXBean.getInputArguments() .

Java's JMX module is not available on Android or on Google App Engine.

8.1.7 Log4j Configuration Location Lookup

Log4j configuration properties. The expressions ${log4j:configLocation} and

${log4j:configParentLocation} respectively provide the absolute path to the log4j

configuration file and its parent folder.

The example below uses this lookup to place log files in a directory relative to the log4j configuration

file.

</PatternLayout>

</File>

8.1.8 Main Arguments Lookup (Application)

This lookup requires that you manually provide the main arguments of the application to Log4j:

8 Lookups 75

import org.apache.logging.log4j.core.lookup.MainMapLookup;

public static void main(String args[]) {

MainMapLookup.setMainArguments(args);

...

}

If the main arguments have been set, this lookup allows applications to retrieve these main argument

values from within the logging configuration. The key that follows the main: prefix can either be a

0-based index into the argument list, or a string, where ${main:myString} is substituted with the

value that follows myString in the main argument list.

For example, suppose the static void main String[] arguments are:

--file foo.txt --verbose -x bar

Then the following substitutions are possible:

Expression Result

${main:0} --file

${main:1} foo.txt

${main:2} --verbose

${main:3} -x

${main:4} bar

${main:--file} foo.txt

${main:-x} bar

${main:bar} null

Example usage:

</PatternLayout>

</File>

8.1.9 Map Lookup

The MapLookup serves several purposes.

1. Provide the base for Properties declared in the configuration file.

2. Retrieve values from MapMessages in LogEvents.

3. Retrieve values set with MapLookup.setMainArguments(String[])

The first item simply means that the MapLookup is used to substitute properties that are defined in the

configuration file. These variables are specified without a prefix - e.g. ${name}. The second usage

allows a value from the current MapMessage, if one is part of the current log event, to be substituted.

In the example below the RoutingAppender will use a different RollingFileAppender for each unique

value of the key named "type" in the MapMessage. Note that when used this way a value for "type"

should be declared in the properties declaration to provide a default value in case the message is not a

8 Lookups 76

MapMessage or the MapMessage does not contain the key. See the Property Substitution section of

the Configuration page for information on how to set the default values.

<Route>

<RollingFile name="Rolling-${map:type}" fileName="${filename}"

filePattern="target/rolling1/test1-${map:type}.%i.log.gz">

</PatternLayout>

</RollingFile>

</Route>

</Routes>

</Routing>

8.1.10 Marker Lookup

The marker lookup allows you to use markers in interesting configurations like a routing appender.

Consider the following YAML configuration and code that logs to different files based on markers:

8 Lookups 77

Configuration:

status: debug

Appenders:

Console:

RandomAccessFile:

- name: SQL_APPENDER

fileName: logs/sql.log

PatternLayout:

Pattern: "%d{ISO8601_BASIC} %-5level %logger{1} %X %msg%n"

- name: PAYLOAD_APPENDER

fileName: logs/payload.log

PatternLayout:

Pattern: "%d{ISO8601_BASIC} %-5level %logger{1} %X %msg%n"

- name: PERFORMANCE_APPENDER

fileName: logs/performance.log

PatternLayout:

Pattern: "%d{ISO8601_BASIC} %-5level %logger{1} %X %msg%n"

Routing:

Routes:

pattern: "$${marker:}"

Route:

- key: PERFORMANCE

ref: PERFORMANCE_APPENDER

- key: PAYLOAD

ref: PAYLOAD_APPENDER

- key: SQL

ref: SQL_APPENDER

Loggers:

Root:

level: trace

AppenderRef:

- ref: ROUTING_APPENDER

public static final Marker SQL = MarkerFactory.getMarker("SQL");

public static final Marker PAYLOAD = MarkerFactory.getMarker("PAYLOAD");

public static final Marker PERFORMANCE = MarkerFactory.getMarker("PERFORMANCE");

final Logger logger = LoggerFactory.getLogger(Logger.ROOT_LOGGER_NAME);

logger.info(SQL, "Message in Sql.log");

logger.info(PAYLOAD, "Message in Payload.log");

logger.info(PERFORMANCE, "Message in Performance.log");

Note the key part of the configuration is pattern: "$${marker:}". This will produce three log

files, each with a log event for a specific marker. Log4j will route the log event with the SQL marker

to sql.log, the log event with the PAYLOAD marker to payload.log, and so on.

You can use the notation "${marker:name}" and "$${marker:name}" to check for the existence

of a marker where name is the marker name. If the marker exists, the expression returns the name,

otherwise null.

8 Lookups 78

8.1.11 Structured Data Lookup

The StructuredDataLookup is very similar to the MapLookup in that it will retrieve values from

StructuredDataMessages. In addition to the Map values it will also return the name portion of

the id (not including the enterprise number) and the type field. The main difference between

the example below and the example for MapMessage is that the "type" is an attribute of the

StructuredDataMessage while "type" would have to be an item in the Map in a MapMessage.

<Route>

<RollingFile name="Rolling-${sd:type}" fileName="${filename}"

filePattern="target/rolling1/test1-${sd:type}.%i.log.gz">

</PatternLayout>

</RollingFile>

</Route>

</Routes>

</Routing>

8.1.12 System Properties Lookup

As it is quite common to define values inside and outside the application by using System Properties,

it is only natural that they should be accessible via a Lookup. As system properties are often defined

outside the application it would be quite common to see something like:

</Appenders>

This lookup also supports default value syntax. In the sample below, when the logPath system

property is undefined, the default value /var/logs is used:

</Appenders>

8.1.13 Web Lookup

The WebLookup allows applications to retrieve variables that are associated with the ServletContext.

In addition to being able to retrieve various fields in the ServletContext, WebLookup supports looking

up values stored as attributes or configured as initialization parameters. The following table lists

various keys that can be retrieved:

Key Description

8 Lookups 79

attr. name Returns the ServletContext attribute with the specified

name

contextPath The context path of the web application

effectiveMajorVersion Gets the major version of the Servlet specification that

the application represented by this ServletContext is

based on.

effectiveMinorVersion Gets the minor version of the Servlet specification that

the application represented by this ServletContext is

based on.

initParam. name Returns the ServletContext initialization parameter

with the specified name

majorVersion Returns the major version of the Servlet API that this

servlet container supports.

minorVersion Returns the minor version of the Servlet API that this

servlet container supports.

rootDir Returns the result of calling getRealPath with a value

of "/".

serverInfo Returns the name and version of the servlet container

on which the servlet is running.

servletContextName Returns the name of the web application as defined

in the display-name element of the deployment

descriptor

Any other key names specified will first be checked to see if a ServletContext attribute exists with that

name and then will be checked to see if an initialization parameter of that name exists. If the key is

located then the corresponding value will be returned.

</Appenders>

9 Appenders 80

9 Appenders

.......................................................................................................................................

9.1 Appenders

Appenders are responsible for delivering LogEvents to their destination. Every Appender must

implement the Appender interface. Most Appenders will extend AbstractAppender which

adds Lifecycle and Filterable support. Lifecycle allows components to finish initialization after

configuration has completed and to perform cleanup during shutdown. Filterable allows the

component to have Filters attached to it which are evaluated during event processing.

Appenders usually are only responsible for writing the event data to the target destination. In most

cases they delegate responsibility for formatting the event to a layout. Some appenders wrap other

appenders so that they can modify the LogEvent, handle a failure in an Appender, route the event to a

subordinate Appender based on advanced Filter criteria or provide similar functionality that does not

directly format the event for viewing.

Appenders always have a name so that they can be referenced from Loggers.

In the tables below, the "Type" column corresponds to the Java type expected. For non-JDK classes,

these should usually be in Log4j Core unless otherwise noted.

9.1.1 AsyncAppender

The AsyncAppender accepts references to other Appenders and causes LogEvents to be written to

them on a separate Thread. Note that exceptions while writing to those Appenders will be hidden from

the application. The AsyncAppender should be configured after the appenders it references to allow it

to shut down properly.

By default, AsyncAppender uses java.util.concurrent.ArrayBlockingQueue which does not require

any external libraries. Note that multi-threaded applications should exercise care when using

this appender as such: the blocking queue is susceptible to lock contention and our tests showed

performance may become worse when more threads are logging concurrently. Consider using lock-

free Async Loggers for optimal performance.

Parameter Name Type Description

AppenderRef String The name of the Appenders to

invoke asynchronously. Multiple

AppenderRef elements can be

configured.

blocking boolean If true, the appender will wait until

there are free slots in the queue. If

false, the event will be written to the

error appender if the queue is full.

The default is true.

shutdownTimeout integer How many milliseconds the

Appender should wait to flush

outstanding log events in the queue

on shutdown. The default is zero

which means to wait forever.

9 Appenders 81

bufferSize integer Specifies the maximum number

of events that can be queued.

The default is 1024. Note that

when using a disruptor-style

BlockingQueue, this buffer size

must be a power of 2.

When the application is

logging faster than the

underlying appender can keep

up with for a long enough

time to fill up the queue, the

behavious is determined by the

AsyncQueueFullPolicy.

errorRef String The name of the Appender to

invoke if none of the appenders can

be called, either due to errors in the

appenders or because the queue is

full. If not specified then errors will

be ignored.

filter Filter A Filter to determine if the

event should be handled by

this Appender. More than one

Filter may be used by using a

CompositeFilter.

name String The name of the Appender.

ignoreExceptions boolean The default is true, causing

exceptions encountered while

appending events to be internally

logged and then ignored. When

set to false exceptions will be

propagated to the caller, instead.

You must set this to false when

wrapping this Appender in a

FailoverAppender.

includeLocation boolean Extracting location is an expensive

operation (it can make logging 5

- 20 times slower). To improve

performance, location is not

included by default when adding

a log event to the queue. You

can change this by setting

includeLocation="true".

BlockingQueueFactory BlockingQueueFactory This element overrides what type

of BlockingQueue to use. See

below documentation for more

details.

AsyncAppender Parameters

There are also a few system properties that can be used to maintain application throughput

even when the underlying appender cannot keep up with the logging rate and the queue is

filling up. See the details for system properties log4j2.AsyncQueueFullPolicy and

log4j2.DiscardThreshold.

A typical AsyncAppender configuration might look like:

9 Appenders 82

<?xml version="1.0" encoding="UTF-8"?>

</PatternLayout>

</File>

</Async>

</Appenders>

</Root>

</Loggers>

</Configuration>

Starting in Log4j 2.7, a custom implementation of BlockingQueue or TransferQueue can be

specified using a BlockingQueueFactory plugin. To override the default BlockingQueueFactory,

specify the plugin inside an <Async/> element like so:

</Async>

</Appenders>

<Root>

</Root>

</Loggers>

</Configuration>

Log4j ships with the following implementations:

Plugin Name Description

ArrayBlockingQueue This is the default implementation that uses

ArrayBlockingQueue.

DisruptorBlockingQueue This uses the Conversant Disruptor implementation of

BlockingQueue. This plugin takes a single optional

attribute, spinPolicy, which corresponds to

JCToolsBlockingQueue This uses JCTools, specifically the MPSC bounded

lock-free queue.

9 Appenders 83

LinkedTransferQueue This uses the new in Java 7 implementation

LinkedTransferQueue. Note that this queue does not

use the bufferSize configuration attribute from

AsyncAppender as LinkedTransferQueue does

not support a maximum capacity.

BlockingQueueFactory Implementations

9.1.2 CassandraAppender

The CassandraAppender writes its output to an Apache Cassandra database.

A keyspace and table must be configured ahead of time, and the columns of

that table are mapped in a configuration file. Each column can specify either a

StringLayout (e.g., a PatternLayout) along with an optional conversion type, or only

a conversion type for org.apache.logging.log4j.spi.ThreadContextMap or

org.apache.logging.log4j.spi.ThreadContextStack to store the MDC or NDC in a map

or list column respectively. A conversion type compatible with java.util.Date will use the log

event timestamp converted to that type (e.g., use java.util.Date to fill a timestamp column type

in Cassandra).

Parameter Name Type Description

batched boolean Whether or not to use batch

statements to write log messages

to Cassandra. By default, this is

false.

batchType BatchStatement.Type The batch type to use when using

batched writes. By default, this is

LOGGED.

bufferSize int The number of log messages to

buffer or batch before writing. By

default, no buffering is done.

clusterName String The name of the Cassandra cluster

to connect to.

9 Appenders 84

columns ColumnMapping[] A list of column mapping

configurations. Each column must

specify a column name. Each

column can have a conversion type

specified by its fully qualified class

name. By default, the conversion

type is String. If the configured

type is assignment-compatible

with ReadOnlyStringMap

/ ThreadContextMap or

ThreadContextStack, then that

column will be populated with

the MDC or NDC respectively.

If the configured type is

assignment-compatible with

java.util.Date, then the

log timestamp will be converted

to that configured date type. If

a literal attribute is given,

then its value will be used as is in

the INSERT query without any

escaping. Otherwise, the layout or

pattern specified will be converted

into the configured type and stored

in that column.

contactPoints SocketAddress[] A list of hosts and ports of

Cassandra nodes to connect to.

These must be valid hostnames or

IP addresses. By default, if a port is

not specified for a host or it is set to

0, then the default Cassandra port

of 9042 will be used. By default,

localhost:9042 will be used.

filter Filter A Filter to determine if the

event should be handled by

this Appender. More than one

Filter may be used by using a

CompositeFilter.

ignoreExceptions boolean The default is true, causing

exceptions encountered while

appending events to be internally

logged and then ignored. When

set to false exceptions will be

propagated to the caller, instead.

You must set this to false when

wrapping this Appender in a

FailoverAppender.

keyspace String The name of the keyspace

containing the table that log

messages will be written to.

name String The name of the Appender.

password String The password to use (along with

the username) to connect to

Cassandra.

9 Appenders 85

table String The name of the table to write log

messages to.

useClockForTimestampGenerator boolean Whether or not to

use the configured

org.apache.logging.log4j.core.util.Clock

as a TimestampGenerator. By

default, this is false.

username String The username to use to connect

to Cassandra. By default, no

username or password is used.

useTls boolean Whether or not to use TLS/SSL

to connect to Cassandra. This is

false by default.

CassandraAppender Parameters

Here is an example CassandraAppender configuration:

</Cassandra>

</Appenders>

</Logger>

</Loggers>

</Configuration>

This example configuration uses the following table schema:

9 Appenders 86

CREATE TABLE logs (

id timeuuid PRIMARY KEY,

timeid timeuuid,

message text,

level text,

marker text,

logger text,

timestamp timestamp,

mdc map<text,text>,

ndc list<text>

);

9.1.3 ConsoleAppender

As one might expect, the ConsoleAppender writes its output to either System.out or System.err with

System.out being the default target. A Layout must be provided to format the LogEvent.

Parameter Name Type Description

filter Filter A Filter to determine if the

event should be handled by

this Appender. More than one

Filter may be used by using a

CompositeFilter.

layout Layout The Layout to use to format the

LogEvent. If no layout is supplied

the default pattern layout of "%m

%n" will be used.

follow boolean Identifies whether the appender

honors reassignments of

System.out or System.err via

System.setOut or System.setErr

made after configuration. Note that

the follow attribute cannot be used

with Jansi on Windows. Cannot be

used with direct.

9 Appenders 87

direct boolean Write directly to

java.io.FileDescriptor

and bypass

java.lang.System.out/.err.

Can give up to 10x performance

boost when the output is

redirected to file or other process.

Cannot be used with Jansi on

Windows. Cannot be used with

follow. Output will not respect

java.lang.System.setOut()/.setErr()

and may get intertwined

with other output to

java.lang.System.out/.err

in a multi-threaded application.

New since 2.6.2. Be aware that this

is a new addition, and it has only

been tested with Oracle JVM on

Linux and Windows so far.

name String The name of the Appender.

ignoreExceptions boolean The default is true, causing

exceptions encountered while

appending events to be internally

logged and then ignored. When

set to false exceptions will be

propagated to the caller, instead.

You must set this to false when

wrapping this Appender in a

FailoverAppender.

target String Either "SYSTEM_OUT" or

"SYSTEM_ERR". The default is

"SYSTEM_OUT".

ConsoleAppender Parameters

A typical Console configuration might look like:

<?xml version="1.0" encoding="UTF-8"?>

</Console>

</Appenders>

</Root>

</Loggers>

</Configuration>

9.1.4 FailoverAppender

The FailoverAppender wraps a set of appenders. If the primary Appender fails the secondary

appenders will be tried in order until one succeeds or there are no more secondaries to try.

9 Appenders 88

Parameter Name Type Description

filter Filter A Filter to determine if the

event should be handled by

this Appender. More than one

Filter may be used by using a

CompositeFilter.

primary String The name of the primary Appender

to use.

failovers String[] The names of the secondary

Appenders to use.

name String The name of the Appender.

retryIntervalSeconds integer The number of seconds that should

pass before retrying the primary

Appender. The default is 60.

ignoreExceptions boolean The default is true, causing

exceptions encountered while

appending events to be internally

logged and then ignored. When

set to false exceptions will be

propagated to the caller, instead.

target String Either "SYSTEM_OUT" or

"SYSTEM_ERR". The default is

"SYSTEM_ERR".

FailoverAppender Parameters

A Failover configuration might look like:

9 Appenders 89

<?xml version="1.0" encoding="UTF-8"?>

<RollingFile name="RollingFile" fileName="logs/app.log" filePattern="logs/app-%d{MM-dd-yyyy}.log.gz"

ignoreExceptions="false">

</PatternLayout>

</RollingFile>

</Console>

</Failovers>

</Failover>

</Appenders>

</Root>

</Loggers>

</Configuration>

9.1.5 FileAppender

The FileAppender is an OutputStreamAppender that writes to the File named in the fileName

parameter. The FileAppender uses a FileManager (which extends OutputStreamManager) to

actually perform the file I/O. While FileAppenders from different Configurations cannot be shared,

the FileManagers can be if the Manager is accessible. For example, two web applications in a

servlet container can have their own configuration and safely write to the same file if Log4j is in a

ClassLoader that is common to both of them.

Parameter Name Type Description

append boolean When true - the default, records

will be appended to the end of the

file. When set to false, the file will

be cleared before new records are

written.

bufferedIO boolean When true - the default, records

will be written to a buffer and the

data will be written to disk when the

buffer is full or, if immediateFlush

is set, when the record is written.

File locking cannot be used with

bufferedIO. Performance tests

have shown that using buffered I/O

significantly improves performance,

even if immediateFlush is enabled.

9 Appenders 90

bufferSize int When bufferedIO is true, this is

the buffer size, the default is 8192

bytes.

createOnDemand boolean The appender creates the file

on-demand. The appender only

creates the file when a log event

passes all filters and is routed to

this appender. Defaults to false.

filter Filter A Filter to determine if the

event should be handled by

this Appender. More than one

Filter may be used by using a

CompositeFilter.

fileName String The name of the file to write to.

If the file, or any of its parent

directories, do not exist, they will be

created.

immediateFlush boolean When set to true - the default,

each write will be followed by

a flush. This will guarantee the

data is written to disk but could

impact performance.

Flushing after every write is

only useful when using this

appender with synchronous

loggers. Asynchronous

loggers and appenders will

automatically flush at the end

of a batch of events, even if

immediateFlush is set to false.

This also guarantees the data

is written to disk but is more

efficient.

layout Layout The Layout to use to format the

LogEvent. If no layout is supplied

the default pattern layout of "%m

%n" will be used.

locking boolean When set to true, I/O operations

will occur only while the file lock

is held allowing FileAppenders

in multiple JVMs and potentially

multiple hosts to write to the

same file simultaneously. This will

significantly impact performance

so should be used carefully.

Furthermore, on many systems

the file lock is "advisory" meaning

that other applications can perform

operations on the file without

acquiring a lock. The default value

is false.

name String The name of the Appender.

9 Appenders 91

ignoreExceptions boolean The default is true, causing

exceptions encountered while

appending events to be internally

logged and then ignored. When

set to false exceptions will be

propagated to the caller, instead.

You must set this to false when

wrapping this Appender in a

FailoverAppender.

filePermissions String File attribute permissions

in POSIX format to apply

whenever the file is created.

Underlying files system shall

support POSIX file attribute

view.

Examples: rw------- or rw-rw-

rw- etc...

fileOwner String File owner to define whenever

the file is created.

Changing file's owner may be

restricted for security reason

and Operation not permitted

IOException thrown. Only

processes with an effective

user ID equal to the user ID

of the file or with appropriate

privileges may change

the ownership of a file if

_POSIX_CHOWN_RESTRICTED

is in effect for path.

Underlying files system shall

support file owner attribute

view.

fileGroup String File group to define whenever

the file is created.

Underlying files system shall

support POSIX file attribute

view.

FileAppender Parameters

Here is a sample File configuration:

9 Appenders 92

<?xml version="1.0" encoding="UTF-8"?>

</PatternLayout>

</File>

</Appenders>

</Root>

</Loggers>

</Configuration>

9.1.6 FlumeAppender

This is an optional component supplied in a separate jar.

Apache Flume is a distributed, reliable, and available system for efficiently collecting, aggregating,

and moving large amounts of log data from many different sources to a centralized data store. The

FlumeAppender takes LogEvents and sends them to a Flume agent as serialized Avro events for

consumption.

The Flume Appender supports three modes of operation.

1. It can act as a remote Flume client which sends Flume events via Avro to a Flume Agent

configured with an Avro Source.

2. It can act as an embedded Flume Agent where Flume events pass directly into Flume for

processing.

3. It can persist events to a local BerkeleyDB data store and then asynchronously send the events to

Flume, similar to the embedded Flume Agent but without most of the Flume dependencies.

Usage as an embedded agent will cause the messages to be directly passed to the Flume Channel and

then control will be immediately returned to the application. All interaction with remote agents will

occur asynchronously. Setting the "type" attribute to "Embedded" will force the use of the embedded

agent. In addition, configuring agent properties in the appender configuration will also cause the

embedded agent to be used.

Parameter Name Type Description

agents Agent[] An array of Agents to which the

logging events should be sent. If

more than one agent is specified

the first Agent will be the primary

and subsequent Agents will be

used in the order specified as

secondaries should the primary

Agent fail. Each Agent definition

supplies the Agents host and port.

The specification of agents and

properties are mutually exclusive.

If both are configured an error will

result.

9 Appenders 93

agentRetries integer The number of times the agent

should be retried before failing to

a secondary. This parameter is

ignored when type="persistent" is

specified (agents are tried once

before failing to the next).

batchSize integer Specifies the number of events

that should be sent as a batch. The

default is 1. This parameter only

applies to the Flume Appender.

compress boolean When set to true the message body

will be compressed using gzip

connectTimeoutMillis integer The number of milliseconds Flume

will wait before timing out the

connection.

dataDir String Directory where the Flume write

ahead log should be written. Valid

only when embedded is set to

true and Agent elements are used

instead of Property elements.

filter Filter A Filter to determine if the

event should be handled by

this Appender. More than one

Filter may be used by using a

CompositeFilter.

eventPrefix String The character string to prepend

to each event attribute in order to

distinguish it from MDC attributes.

The default is an empty string.

flumeEventFactory FlumeEventFactory Factory that generates the

Flume events from Log4j

events. The default factory is the

FlumeAvroAppender itself.

layout Layout The Layout to use to format the

LogEvent. If no layout is specified

RFC5424Layout will be used.

lockTimeoutRetries integer The number of times to retry if a

LockConflictException occurs while

writing to Berkeley DB. The default

is 5.

maxDelayMillis integer The maximum number of

milliseconds to wait for batchSize

events before publishing the batch.

mdcExcludes String A comma separated list of mdc

keys that should be excluded from

the FlumeEvent. This is mutually

exclusive with the mdcIncludes

attribute.

9 Appenders 94

mdcIncludes String A comma separated list of mdc

keys that should be included in

the FlumeEvent. Any keys in the

MDC not found in the list will be

excluded. This option is mutually

exclusive with the mdcExcludes

attribute.

mdcRequired String A comma separated list of mdc

keys that must be present in the

MDC. If a key is not present a

LoggingException will be thrown.

mdcPrefix String A string that should be prepended

to each MDC key in order to

distinguish it from event attributes.

The default string is "mdc:".

name String The name of the Appender.

properties Property[] One or more Property elements

that are used to configure the

Flume Agent. The properties

must be configured without

the agent name (the appender

name is used for this) and no

sources can be configured.

Interceptors can be specified for

the source using "sources.log4j-

source.interceptors". All other

Flume configuration properties

are allowed. Specifying both

Agent and Property elements

will result in an error.

When used to configure in

Persistent mode the valid

properties are:

1. "keyProvider" to specify the

name of the plugin to provide

the secret key for encryption.

requestTimeoutMillis integer The number of milliseconds Flume

will wait before timing out the

request.

ignoreExceptions boolean The default is true, causing

exceptions encountered while

appending events to be internally

logged and then ignored. When

set to false exceptions will be

propagated to the caller, instead.

You must set this to false when

wrapping this Appender in a

FailoverAppender.

9 Appenders 95

type enumeration One of "Avro", "Embedded", or

"Persistent" to indicate which

variation of the Appender is

desired.

FlumeAppender Parameters

A sample FlumeAppender configuration that is configured with a primary and a secondary agent,

compresses the body, and formats the body using the RFC5424Layout:

<?xml version="1.0" encoding="UTF-8"?>

</Flume>

</Appenders>

</Root>

</Loggers>

</Configuration>

A sample FlumeAppender configuration that is configured with a primary and a secondary agent,

compresses the body, formats the body using the RFC5424Layout, and persists encrypted events to

disk:

<?xml version="1.0" encoding="UTF-8"?>

<Property name="keyProvider">MySecretProvider</Property>

</Flume>

</Appenders>

</Root>

</Loggers>

</Configuration>

A sample FlumeAppender configuration that is configured with a primary and a secondary agent,

compresses the body, formats the body using RFC5424Layout and passes the events to an embedded

Flume Agent.

9 Appenders 96

<?xml version="1.0" encoding="UTF-8"?>

</Flume>

</Console>

</Appenders>

</Logger>

</Root>

</Loggers>

</Configuration>

A sample FlumeAppender configuration that is configured with a primary and a secondary agent

using Flume configuration properties, compresses the body, formats the body using RFC5424Layout

and passes the events to an embedded Flume Agent.

9 Appenders 97

<?xml version="1.0" encoding="UTF-8"?>

<Property name="channels.file.checkpointDir">target/file-channel/checkpoint</Property>

<Property name="channels.file.dataDirs">target/file-channel/data</Property>

<Property name="sinks">agent1 agent2</Property>

<Property name="sinkgroups">group1</Property>

<Property name="sinkgroups.group1.sinks">agent1 agent2</Property>

<Property name="sinkgroups.group1.processor.type">failover</Property>

</Flume>

</Console>

</Appenders>

</Logger>

</Root>

</Loggers>

</Configuration>

9.1.7 JDBCAppender

The JDBCAppender writes log events to a relational database table using standard JDBC. It

can be configured to obtain JDBC connections using a JNDI DataSource or a custom factory

method. Whichever approach you take, it must be backed by a connection pool. Otherwise, logging

performance will suffer greatly. If batch statements are supported by the configured JDBC driver

and a bufferSize is configured to be a positive number, then log events will be batched. Note

that as of Log4j 2.8, there are two ways to configure log event to column mappings: the original

ColumnConfig style that only allows strings and timestamps, and the new ColumnMapping plugin

that uses Log4j's built-in type conversion to allow for more data types (this is the same plugin as in

the Cassandra Appender).

9 Appenders 98

To get off the ground quickly during development, an alternative to using a connection source based

on JNDI is to use the non-pooling DriverManager connection source. This connection source uses a

JDBC connection string, a user name, and a password. Optionally, you can also use properties.

Parameter Name Type Description

name String Required. The name of the

Appender.

ignoreExceptions boolean The default is true, causing

exceptions encountered while

appending events to be internally

logged and then ignored. When

set to false exceptions will be

propagated to the caller, instead.

You must set this to false when

wrapping this Appender in a

FailoverAppender.

filter Filter A Filter to determine if the

event should be handled by

this Appender. More than one

Filter may be used by using a

CompositeFilter.

bufferSize int If an integer greater than 0, this

causes the appender to buffer log

events and flush whenever the

buffer reaches this size.

connectionSource ConnectionSource Required. The connections source

from which database connections

should be retrieved.

tableName String Required. The name of the

database table to insert log events

into.

columnConfigs ColumnConfig[] Required (and/or

columnMappings). Information

about the columns that log event

data should be inserted into

and how to insert that data. This

is represented with multiple

<Column> elements.

9 Appenders 99

columnMappings ColumnMapping[] Required (and/or columnConfigs).

A list of column mapping

configurations. Each column must

specify a column name. Each

column can have a conversion type

specified by its fully qualified class

name. By default, the conversion

type is String. If the configured

type is assignment-compatible

with ReadOnlyStringMap

/ ThreadContextMap or

ThreadContextStack, then that

column will be populated with

the MDC or NDC respectively

(this is database-specific how

they handle inserting a Map or

List value). If the configured

type is assignment-compatible with

java.util.Date, then the

log timestamp will be converted

to that configured date type. If the

configured type is assignment-

compatible with java.sql.Clob

or java.sql.NClob, then the

formatted event will be set as a

Clob or NClob respectively (similar

to the traditional ColumnConfig

plugin). If a literal attribute is

given, then its value will be used as

is in the INSERT query without any

escaping. Otherwise, the layout or

pattern specified will be converted

into the configured type and stored

in that column.

JDBCAppender Parameters

When configuring the JDBCAppender, you must specify a ConnectionSource implementation

from which the Appender gets JDBC connections. You must use exactly one of the following nested

elements:

•<DataSource>: Uses JNDI.

•<ConnectionFactory>: Points to a class-method pair to provide JDBC connections.

•<DriverManager>: A quick and dirty way to get off the ground, no connection pooling.

•<PoolingDriver>: Uses Apache Commons DBCP to provide connection pooling.

Parameter Name Type Description

9 Appenders 100

jndiName String Required. The full, prefixed

JNDI name that the

javax.sql.DataSource

is bound to, such as java:/

comp/env/jdbc/

LoggingDatabase. The

DataSource must be backed

by a connection pool; otherwise,

logging will be very slow.

DataSource Parameters

Parameter Name Type Description

class Class Required. The fully qualified name

of a class containing a static

factory method for obtaining JDBC

connections.

method Method Required. The name of a static

factory method for obtaining

JDBC connections. This method

must have no parameters and

its return type must be either

java.sql.Connection or

DataSource. If the method

returns Connections, it must

obtain them from a connection

pool (and they will be returned to

the pool when Log4j is done with

them); otherwise, logging will be

very slow. If the method returns a

DataSource, the DataSource

will only be retrieved once, and it

must be backed by a connection

pool for the same reasons.

ConnectionFactory Parameters

Parameter Name Type Description

connectionString String Required. The driver-specific JDBC

connection string.

userName String The database user name. You

cannot specify both properties and

a user name or password.

password String The database password. You

cannot specify both properties and

a user name or password.

driverClassName String The JDBC driver class name.

Some old JDBC Driver can only

be discovered by explicitly loading

them by class name.

9 Appenders 101

properties Property[] A list of properties. You cannot

specify both properties and a user

name or password.

DriverManager Parameters

Parameter Name Type Description

DriverManager parameters DriverManager parameters This connection source inherits all

parameter from the DriverManager

connection source.

poolName String The pool name used to pool

JDBC Connections. Defaults

to example. You can use the

JDBC connection string prefix

jdbc:apache:commons:dbcp:

followed by the pool name if you

want to use a pooled connection

elsewhere. For example:

jdbc:apache:commons:dbcp:example.

PoolingDriver Parameters (Apache Commons DBCP)

When configuring the JDBCAppender, use the nested <Column> elements to specify which columns

in the table should be written to and how to write to them. The JDBCAppender uses this information

to formulate a PreparedStatement to insert records without SQL injection vulnerability.

Parameter Name Type Description

name String Required. The name of the

database column.

pattern String Use this attribute to insert a value

or values from the log event in this

column using a PatternLayout

pattern. Simply specify any legal

pattern in this attribute. Either

this attribute, literal, or

isEventTimestamp="true"

must be specified, but not more

than one of these.

9 Appenders 102

literal String Use this attribute to insert a

literal value in this column. The

value will be included directly

in the insert SQL, without any

quoting (which means that if

you want this to be a string,

your value should contain

single quotes around it like

this: literal="'Literal

String'"). This is especially

useful for databases that don't

support identity columns.

For example, if you are using

Oracle you could specify

literal="NAME_OF_YOUR_SEQUENCE.NEXTVAL"

to insert a unique ID in

an ID column. Either this

attribute, pattern, or

isEventTimestamp="true"

must be specified, but not more

than one of these.

parameter String Use this attribute to insert an

expression with a parameter

marker '?' in this column. The

value will be included directly

in the insert SQL, without any

quoting (which means that if

you want this to be a string,

your value should contain

single quotes around it like this:

<ColumnMapping

name="instant"

parameter="TIMESTAMPADD('MILLISECOND', ?,

TIMESTAMP

'1970-01-01')"/>

You can only specify one of

literal or parameter.

isEventTimestamp boolean Use this attribute to insert the

event timestamp in this column,

which should be a SQL datetime.

The value will be inserted as a

java.sql.Types.TIMESTAMP.

Either this attribute (equal

to true), pattern, or

isEventTimestamp must be

specified, but not more than one of

these.

9 Appenders 103

isUnicode boolean This attribute is ignored unless

pattern is specified. If

true or omitted (default),

the value will be inserted as

unicode ( setNString or

setNClob). Otherwise, the value

will be inserted non-unicode (

setString or setClob).

isClob boolean This attribute is ignored unless

pattern is specified. Use this

attribute to indicate that the column

stores Character Large Objects

(CLOBs). If true, the value will be

inserted as a CLOB ( setClob or

setNClob). If false or omitted

(default), the value will be inserted

as a VARCHAR or NVARCHAR (

setString or setNString).

Column Parameters

Parameter Name Type Description

name String Required. The name of the

database column.

pattern String Use this attribute to insert a value

or values from the log event in this

column using a PatternLayout

pattern. Simply specify any legal

pattern in this attribute. Either

this attribute, literal, or

isEventTimestamp="true"

must be specified, but not more

than one of these.

literal String Use this attribute to insert a literal

value in this column. The value

will be included directly in the

insert SQL, without any quoting

(which means that if you want this

to be a string, your value should

contain single quotes around it

like this: literal="'Literal

String'"). This is especially

useful for databases that don't

support identity columns. For

example, if you are using

Oracle you could specify

literal="NAME_OF_YOUR_SEQUENCE.NEXTVAL"

to insert a unique ID in

an ID column. Either this

attribute, pattern, or

isEventTimestamp="true"

must be specified, but not more

than one of these.

layout Layout The Layout to format the LogEvent.

9 Appenders 104

type String Conversion type name, a fully-

qualified class name.

ColumnMapping Parameters

Here are a couple sample configurations for the JDBCAppender, as well as a sample factory

implementation that uses Commons Pooling and Commons DBCP to pool database connections:

<?xml version="1.0" encoding="UTF-8"?>

</JDBC>

</Appenders>

</Root>

</Loggers>

</Configuration>

<?xml version="1.0" encoding="UTF-8"?>

</JDBC>

</Appenders>

</Root>

</Loggers>

</Configuration>

9 Appenders 105

package net.example.db;

import java.sql.Connection;

import java.sql.SQLException;

import java.util.Properties;

import javax.sql.DataSource;

import org.apache.commons.dbcp.DriverManagerConnectionFactory;

import org.apache.commons.dbcp.PoolableConnection;

import org.apache.commons.dbcp.PoolableConnectionFactory;

import org.apache.commons.dbcp.PoolingDataSource;

import org.apache.commons.pool.impl.GenericObjectPool;

public class ConnectionFactory {

private static interface Singleton {

final ConnectionFactory INSTANCE = new ConnectionFactory();

}

private final DataSource dataSource;

private ConnectionFactory() {

Properties properties = new Properties();

properties.setProperty("user", "logging");

properties.setProperty("password", "abc123"); // or get properties from some configuration file

GenericObjectPool<PoolableConnection> pool = new GenericObjectPool<PoolableConnection>();

DriverManagerConnectionFactory connectionFactory = new DriverManagerConnectionFactory(

"jdbc:mysql://example.org:3306/exampleDb", properties

);

new PoolableConnectionFactory(

connectionFactory, pool, null, "SELECT 1", 3, false, false, Connection.TRANSACTION_READ_COMMITTED

);

this.dataSource = new PoolingDataSource(pool);

}

public static Connection getDatabaseConnection() throws SQLException {

return Singleton.INSTANCE.dataSource.getConnection();

}

This appender is MapMessage-aware.

The following configuration uses a MessageLayout to indicate that the Appender should match the

keys of a MapMessage to the names of ColumnMappings when setting the values of the Appender's

SQL INSERT statement. This let you insert rows for custom values in a database table based on a

Log4j MapMessage instead of values from LogEvents.

9 Appenders 106

</Console>

</Jdbc>

</Appenders>

</Logger>

</Root>

</Loggers>

</Configuration>

9.1.8 JMS Appender

The JMS Appender sends the formatted log event to a JMS Destination.

Note that in Log4j 2.0, this appender was split into a JMSQueueAppender and a JMSTopicAppender.

Starting in Log4j 2.1, these appenders were combined into the JMS Appender which makes no

distinction between queues and topics. However, configurations written for 2.0 which use the

<JMSQueue/> or <JMSTopic/> elements will continue to work with the new <JMS/> configuration

element.

Parameter Name Type Default Description

factoryBindingName String Required The name to locate in

the Context that provides

the ConnectionFactory.

This can be any

subinterface of

ConnectionFactory

as well.

9 Appenders 107

factoryName String Required The fully qualified

class name that should

be used to define

the Initial Context

Factory as defined in

INITIAL_CONTEXT_FACTORY.

If a factoryName is

specified without a

providerURL a warning

message will be logged

as this is likely to cause

problems.

filter Filter null A Filter to determine

if the event should be

handled by this Appender.

More than one Filter

may be used by using a

CompositeFilter.

layout Layout Required The Layout to use to

format the LogEvent. New

since 2.9, in previous

versions SerializedLayout

was default.

name String Required The name of the

Appender.

password String null The password to use

to create the JMS

connection.

providerURL String Required The URL of the provider

to use as defined by

PROVIDER_URL.

destinationBindingName String Required The name to use to

locate the Destination.

This can be a Queue

or Topic, and as such,

the attribute names

queueBindingName

and

topicBindingName

are aliases to maintain

compatibility with the

Log4j 2.0 JMS appenders.

securityPrincipalName String null The name of the

identity of the Principal

as specified by

SECURITY_PRINCIPAL.

If a securityPrincipalName

is specified without

securityCredentials a

warning message will be

logged as this is likely to

cause problems.

9 Appenders 108

securityCredentials String null The security credentials

for the principal

as specified by

SECURITY_CREDENTIALS.

ignoreExceptions boolean true When true, exceptions

caught while appending

events are internally

logged and then ignored.

When false exceptions

are propagated to the

caller. You must set

this to false when

wrapping this Appender in

a FailoverAppender.

immediateFail boolean false When set to true, log

events will not wait to

try to reconnect and will

fail immediately if the

JMS resources are not

available. New in 2.9.

reconnectIntervalMillis long 5000 If set to a value greater

than 0, after an error, the

JMSManager will attempt

to reconnect to the broker

after waiting the specified

number of milliseconds.

If the reconnect fails

then an exception will

be thrown (which can be

caught by the application

if ignoreExceptions

is set to false). New in

2.9.

urlPkgPrefixes String null A colon-separated list

of package prefixes for

the class name of the

factory class that will

create a URL context

factory as defined by

URL_PKG_PREFIXES.

userName String null The user id used to create

the JMS connection.

JMS Appender Parameters

Here is a sample JMS Appender configuration:

9 Appenders 109

<?xml version="1.0" encoding="UTF-8"?>

<JMS name="jmsQueue" destinationBindingName="MyQueue"

factoryBindingName="MyQueueConnectionFactory">

</JMS>

</Appenders>

</Root>

</Loggers>

</Configuration>

To map your Log4j MapMessages to JMS javax.jms.MapMessages, set the layout of the appender

to MessageLayout with <MessageLayout /> (Since 2.9.):

<?xml version="1.0" encoding="UTF-8"?>

<JMS name="jmsQueue" destinationBindingName="MyQueue"

factoryBindingName="MyQueueConnectionFactory">

</JMS>

</Appenders>

</Root>

</Loggers>

</Configuration>

9.1.9 JPAAppender

As of Log4j 2.11.0, JPA support has moved from the existing module logj-core to the new module

log4j-jpa.

The JPAAppender writes log events to a relational database table using the Java Persistence

API 2.1. It requires the API and a provider implementation be on the classpath. It also requires

a decorated entity configured to persist to the table desired. The entity should either extend

org.apache.logging.log4j.core.appender.db.jpa.BasicLogEventEntity

(if you mostly want to use the default mappings) and provide at least an @Id property, or

org.apache.logging.log4j.core.appender.db.jpa.AbstractLogEventWrapperEntity

(if you want to significantly customize the mappings). See the Javadoc for these two classes for

more information. You can also consult the source code of these two classes as an example of how to

implement the entity.

Parameter Name Type Description

name String Required. The name of the

Appender.

9 Appenders 110

ignoreExceptions boolean The default is true, causing

exceptions encountered while

appending events to be internally

logged and then ignored. When

set to false exceptions will be

propagated to the caller, instead.

You must set this to false when

wrapping this Appender in a

FailoverAppender.

filter Filter A Filter to determine if the

event should be handled by

this Appender. More than one

Filter may be used by using a

CompositeFilter.

bufferSize int If an integer greater than 0, this

causes the appender to buffer log

events and flush whenever the

buffer reaches this size.

entityClassName String Required. The fully qualified

name of the concrete

LogEventWrapperEntity

implementation that has JPA

annotations mapping it to a

database table.

persistenceUnitName String Required. The name of the JPA

persistence unit that should be

used for persisting log events.

JPAAppender Parameters

Here is a sample configuration for the JPAAppender. The first XML sample is the Log4j

configuration file, the second is the persistence.xml file. EclipseLink is assumed here, but

any JPA 2.1 or higher provider will do. You should always create a separate persistence unit

for logging, for two reasons. First, <shared-cache-mode> must be set to "NONE," which is

usually not desired in normal JPA usage. Also, for performance reasons the logging entity should

be isolated in its own persistence unit away from all other entities and you should use a non-JTA

data source. Note that your persistence unit must also contain <class> elements for all of the

org.apache.logging.log4j.core.appender.db.jpa.converter converter classes.

<?xml version="1.0" encoding="UTF-8"?>

<JPA name="databaseAppender" persistenceUnitName="loggingPersistenceUnit"

entityClassName="com.example.logging.JpaLogEntity" />

</Appenders>

</Root>

</Loggers>

</Configuration>

9 Appenders 111

<?xml version="1.0" encoding="UTF-8"?>

<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence

http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd"

version="2.1">

<persistence-unit name="loggingPersistenceUnit" transaction-type="RESOURCE_LOCAL">

<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>

<class>org.apache.logging.log4j.core.appender.db.jpa.converter.ContextMapAttributeConverter</class>

<class>org.apache.logging.log4j.core.appender.db.jpa.converter.ContextMapJsonAttributeConverter</class>

<class>org.apache.logging.log4j.core.appender.db.jpa.converter.ContextStackAttributeConverter</class>

<class>org.apache.logging.log4j.core.appender.db.jpa.converter.ContextStackJsonAttributeConverter</class>

<class>org.apache.logging.log4j.core.appender.db.jpa.converter.MarkerAttributeConverter</class>

<class>org.apache.logging.log4j.core.appender.db.jpa.converter.MessageAttributeConverter</class>

<class>org.apache.logging.log4j.core.appender.db.jpa.converter.StackTraceElementAttributeConverter</class>

<class>org.apache.logging.log4j.core.appender.db.jpa.converter.ThrowableAttributeConverter</class>

<class>com.example.logging.JpaLogEntity</class>

<non-jta-data-source>jdbc/LoggingDataSource</non-jta-data-source>

<shared-cache-mode>NONE</shared-cache-mode>

</persistence-unit>

</persistence>

package com.example.logging;

...

@Entity

@Table(name="application_log", schema="dbo")

public class JpaLogEntity extends BasicLogEventEntity {

private static final long serialVersionUID = 1L;

private long id = 0L;

public TestEntity() {

super(null);

}

public TestEntity(LogEvent wrappedEvent) {

super(wrappedEvent);

}

@Id

@GeneratedValue(strategy = GenerationType.IDENTITY)

@Column(name = "id")

public long getId() {

return this.id;

}

public void setId(long id) {

this.id = id;

}

// If you want to override the mapping of any properties mapped in BasicLogEventEntity,

// just override the getters and re-specify the annotations.

}

9 Appenders 112

package com.example.logging;

...

@Entity

@Table(name="application_log", schema="dbo")

public class JpaLogEntity extends AbstractLogEventWrapperEntity {

private static final long serialVersionUID = 1L;

private long id = 0L;

public TestEntity() {

super(null);

}

public TestEntity(LogEvent wrappedEvent) {

super(wrappedEvent);

}

@Id

@GeneratedValue(strategy = GenerationType.IDENTITY)

@Column(name = "logEventId")

public long getId() {

return this.id;

}

public void setId(long id) {

this.id = id;

}

@Override

@Enumerated(EnumType.STRING)

@Column(name = "level")

public Level getLevel() {

return this.getWrappedEvent().getLevel();

}

@Override

@Column(name = "logger")

public String getLoggerName() {

return this.getWrappedEvent().getLoggerName();

}

@Override

@Column(name = "message")

@Convert(converter = MyMessageConverter.class)

public Message getMessage() {

return this.getWrappedEvent().getMessage();

}

...

}

9.1.10 HttpAppender

The HttpAppender sends log events over HTTP. A Layout must be provided to format the LogEvent.

9 Appenders 113

Will set the Content-Type header according to the layout. Additional headers can be specified with

embedded Property elements.

Will wait for response from server, and throw error if no 2xx response is received.

Implemented with HttpURLConnection.

Parameter Name Type Description

name String The name of the Appender.

filter Filter A Filter to determine if the

event should be handled by

this Appender. More than one

Filter may be used by using a

CompositeFilter.

layout Layout The Layout to use to format the

LogEvent.

Ssl SslConfiguration Contains the configuration for

the KeyStore and TrustStore for

https. Optional, uses Java runtime

defaults if not specified. See SSL

verifyHostname boolean Whether to verify server hostname

against certificate. Only valid for

https. Optional, defaults to true

url string The URL to use. The URL scheme

must be "http" or "https".

method string The HTTP method to use. Optional,

default is "POST".

connectTimeoutMillis integer The connect timeout in

milliseconds. Optional, default is 0

(infinite timeout).

readTimeoutMillis integer The socket read timeout in

milliseconds. Optional, default is 0

(infinite timeout).

headers Property[] Additional HTTP headers to use.

The values support lookups.

ignoreExceptions boolean The default is true, causing

exceptions encountered while

appending events to be internally

logged and then ignored. When

set to false exceptions will be

propagated to the caller, instead.

You must set this to false when

wrapping this Appender in a

FailoverAppender.

HttpAppender Parameters

Here is a sample HttpAppender configuration snippet:

9 Appenders 114

<?xml version="1.0" encoding="UTF-8"?>

...

<SSL>

</SSL>

</Http>

</Appenders>

9.1.11 KafkaAppender

The KafkaAppender logs events to an Apache Kafka topic. Each log event is sent as a Kafka record.

Parameter Name Type Description

topic String The Kafka topic to use. Required.

key String The key that will be sent to Kafka

with every message. Optional value

defaulting to null. Any of the

Lookups) can be included.

filter Filter A Filter to determine if the

event should be handled by

this Appender. More than one

Filter may be used by using a

CompositeFilter.

layout Layout The Layout to use to format the

LogEvent. Required, there is

no default. New since 2.9, in

previous versions <PatternLayout

pattern="%m"/> was default.

name String The name of the Appender.

Required.

ignoreExceptions boolean The default is true, causing

exceptions encountered while

appending events to be internally

logged and then ignored. When

set to false exceptions will be

propagated to the caller, instead.

You must set this to false when

wrapping this Appender in a

FailoverAppender.

9 Appenders 115

syncSend boolean The default is true, causing

sends to block until the record

has been acknowledged by the

Kafka server. When set to false

sends return immediately, allowing

for lower latency and significantly

higher throughput. New since

2.8. Be aware that this is a new

addition, and it has not been

extensively tested. Any failure

sending to Kafka will be reported

as error to StatusLogger and the

log event will be dropped (the

ignoreExceptions parameter will not

be effective). Log events may arrive

out of order to the Kafka server.

properties Property[] You can set properties in Kafka

producer properties. You need to

set the bootstrap.servers

property, there are sensible default

values for the others. Do not set

the value.serializer nor

key.serializer properties.

KafkaAppender Parameters

Here is a sample KafkaAppender configuration snippet:

<?xml version="1.0" encoding="UTF-8"?>

...

<Property name="bootstrap.servers">localhost:9092</Property>

</Kafka>

</Appenders>

This appender is synchronous by default and will block until the record has been acknowledged by

the Kafka server, timeout for this can be set with the timeout.ms property (defaults to 30 seconds).

Wrap with Async appender and/or set syncSend to false to log asynchronously.

This appender requires the Kafka client library. Note that you need to use a version of the Kafka

client library matching the Kafka server used.

Note:Make sure to not let org.apache.kafka log to a Kafka appender on DEBUG level, since that

will cause recursive logging:

<?xml version="1.0" encoding="UTF-8"?>

...

</Root>

</Loggers>

9 Appenders 116

9.1.12 MemoryMappedFileAppender

New since 2.1. Be aware that this is a new addition, and although it has been tested on several

platforms, it does not have as much track record as the other file appenders.

The MemoryMappedFileAppender maps a part of the specified file into memory and writes log

events to this memory, relying on the operating system's virtual memory manager to synchronize the

changes to the storage device. The main benefit of using memory mapped files is I/O performance.

Instead of making system calls to write to disk, this appender can simply change the program's

local memory, which is orders of magnitude faster. Also, in most operating systems the memory

region mapped actually is the kernel's page cache (file cache), meaning that no copies need to be

created in user space. (TODO: performance tests that compare performance of this appender to

RandomAccessFileAppender and FileAppender.)

There is some overhead with mapping a file region into memory, especially very large regions (half

a gigabyte or more). The default region size is 32 MB, which should strike a reasonable balance

between the frequency and the duration of remap operations. (TODO: performance test remapping

various sizes.)

Similar to the FileAppender and the RandomAccessFileAppender, MemoryMappedFileAppender uses

a MemoryMappedFileManager to actually perform the file I/O. While MemoryMappedFileAppender

from different Configurations cannot be shared, the MemoryMappedFileManagers can be if the

Manager is accessible. For example, two web applications in a servlet container can have their own

configuration and safely write to the same file if Log4j is in a ClassLoader that is common to both of

them.

Parameter Name Type Description

append boolean When true - the default, records

will be appended to the end of the

file. When set to false, the file will

be cleared before new records are

written.

fileName String The name of the file to write to.

If the file, or any of its parent

directories, do not exist, they will be

created.

filters Filter A Filter to determine if the

event should be handled by

this Appender. More than one

Filter may be used by using a

CompositeFilter.

9 Appenders 117

immediateFlush boolean When set to true, each write

will be followed by a call to

MappedByteBuffer.force().

This will guarantee the data is

written to the storage device.

The default for this parameter is

false. This means that the data

is written to the storage device

even if the Java process crashes,

but there may be data loss if the

operating system crashes.

Note that manually forcing

a sync on every log event

loses most of the performance

benefits of using a memory

mapped file.

Flushing after every write is

only useful when using this

appender with synchronous

loggers. Asynchronous

loggers and appenders will

automatically flush at the end

of a batch of events, even if

immediateFlush is set to false.

This also guarantees the data

is written to disk but is more

efficient.

regionLength int The length of the mapped region,

defaults to 32 MB (32 * 1024

* 1024 bytes). This parameter

must be a value between 256 and

1,073,741,824 (1 GB or 2^30);

values outside this range will be

adjusted to the closest valid value.

Log4j will round the specified value

up to the nearest power of two.

layout Layout The Layout to use to format the

LogEvent. If no layout is supplied

the default pattern layout of "%m

%n" will be used.

name String The name of the Appender.

ignoreExceptions boolean The default is true, causing

exceptions encountered while

appending events to be internally

logged and then ignored. When

set to false exceptions will be

propagated to the caller, instead.

You must set this to false when

wrapping this Appender in a

FailoverAppender.

MemoryMappedFileAppender Parameters

9 Appenders 118

Here is a sample MemoryMappedFile configuration:

<?xml version="1.0" encoding="UTF-8"?>

</PatternLayout>

</MemoryMappedFile>

</Appenders>

</Root>

</Loggers>

</Configuration>

9.1.13 NoSQLAppender

The NoSQLAppender writes log events to a NoSQL database using an internal lightweight provider

interface. Provider implementations currently exist for MongoDB and Apache CouchDB, and writing

a custom provider is quite simple.

Parameter Name Type Description

name String Required. The name of the

Appender.

ignoreExceptions boolean The default is true, causing

exceptions encountered while

appending events to be internally

logged and then ignored. When

set to false exceptions will be

propagated to the caller, instead.

You must set this to false when

wrapping this Appender in a

FailoverAppender.

filter Filter A Filter to determine if the

event should be handled by

this Appender. More than one

Filter may be used by using a

CompositeFilter.

bufferSize int If an integer greater than 0, this

causes the appender to buffer log

events and flush whenever the

buffer reaches this size.

NoSqlProvider NoSQLProvider<C extends

NoSQLConnection<W, T extends

NoSQLObject<W>>>

Required. The NoSQL provider that

provides connections to the chosen

NoSQL database.

NoSQLAppender Parameters

9 Appenders 119

You specify which NoSQL provider to use by specifying the appropriate configuration element within

the <NoSql> element. The types currently supported are <MongoDb> and <CouchDb>. To create

your own custom provider, read the JavaDoc for the NoSQLProvider, NoSQLConnection, and

NoSQLObject classes and the documentation about creating Log4j plugins. We recommend you

review the source code for the MongoDB and CouchDB providers as a guide for creating your own

provider.

The following example demonstrates how log events are persisted in NoSQL databases if represented

in a JSON format:

9 Appenders 120

{

"level": "WARN",

"loggerName": "com.example.application.MyClass",

"message": "Something happened that you might want to know about.",

"source": {

"className": "com.example.application.MyClass",

"methodName": "exampleMethod",

"fileName": "MyClass.java",

"lineNumber": 81

"marker": {

"name": "SomeMarker",

"parent" {

"name": "SomeParentMarker"

}

"threadName": "Thread-1",

"millis": 1368844166761,

"date": "2013-05-18T02:29:26.761Z",

"thrown": {

"type": "java.sql.SQLException",

"message": "Could not insert record. Connection lost.",

"stackTrace": [

{ "className": "org.example.sql.driver.PreparedStatement$1", "methodName": "responder", "fileName": "PreparedStatement.java", "lineNumber": 1049 },

{ "className": "org.example.sql.driver.PreparedStatement", "methodName": "executeUpdate", "fileName": "PreparedStatement.java", "lineNumber": 738 },

{ "className": "com.example.application.MyClass", "methodName": "exampleMethod", "fileName": "MyClass.java", "lineNumber": 81 },

{ "className": "com.example.application.MainClass", "methodName": "main", "fileName": "MainClass.java", "lineNumber": 52 }

"cause": {

"type": "java.io.IOException",

"message": "Connection lost.",

"stackTrace": [

{ "className": "java.nio.channels.SocketChannel", "methodName": "write", "fileName": null, "lineNumber": -1 },

{ "className": "org.example.sql.driver.PreparedStatement$1", "methodName": "responder", "fileName": "PreparedStatement.java", "lineNumber": 1032 },

{ "className": "org.example.sql.driver.PreparedStatement", "methodName": "executeUpdate", "fileName": "PreparedStatement.java", "lineNumber": 738 },

{ "className": "com.example.application.MyClass", "methodName": "exampleMethod", "fileName": "MyClass.java", "lineNumber": 81 },

{ "className": "com.example.application.MainClass", "methodName": "main", "fileName": "MainClass.java", "lineNumber": 52 }

]

}

"contextMap": {

"ID": "86c3a497-4e67-4eed-9d6a-2e5797324d7b",

"username": "JohnDoe"

"contextStack": [

"topItem",

"anotherItem",

"bottomItem"

]

}

9 Appenders 121

9.1.14 NoSQLAppender for MongoDB

Starting with Log4 2.11.0, we provide two MongoDB modules:

•log4j-mongodb2 defines the configuration element MongoDb2 matching the MongoDB

Driver version 2.

•log4j-mongodb3 defines the configuration element MongoDb3 matching the MongoDB

Driver version 3.

We no longer provide the module log4j-mongodb.

The module log4j-mongodb2 aliases the old configuration element MongoDb to MongoDb2.

9.1.15 NoSQLAppender for MongoDB 2

This section details specializations of the NoSQLAppender provider for MongoDB using the

MongoDB driver version 2. The NoSQLAppender Appender writes log events to a NoSQL database

using an internal lightweight provider interface.

Parameter Name Type Description

collectionName String Required. The name of the

MongoDB collection to insert the

events into.

writeConcernConstant Field By default, the MongoDB provider

inserts records with the instructions

com.mongodb.WriteConcern.ACKNOWLEDGED.

Use this optional attribute to specify

the name of a constant other than

ACKNOWLEDGED.

writeConcernConstantClass Class If you specify

writeConcernConstant,

you can use this attribute to

specify a class other than

com.mongodb.WriteConcern

to find the constant on (to create

your own custom instructions).

factoryClassName Class To provide a connection to

the MongoDB database, you

can use this attribute and

factoryMethodName to specify

a class and static method to get the

connection from. The method must

return a com.mongodb.DB or a

com.mongodb.MongoClient.

If the DB is not authenticated, you

must also specify a username

and password. If you use the

factory method for providing a

connection, you must not specify

the databaseName, server, or

port attributes.

factoryMethodName Method See the documentation for attribute

factoryClassName.

9 Appenders 122

databaseName String If you do not specify a

factoryClassName and

factoryMethodName for

providing a MongoDB connection,

you must specify a MongoDB

database name using this

attribute. You must also specify

a username and password.

You can optionally also specify a

server (defaults to localhost),

and a port (defaults to the default

MongoDB port).

server String See the documentation for attribute

databaseName.

port int See the documentation for attribute

databaseName.

username String See the documentation for

attributes databaseName and

factoryClassName.

password String See the documentation for

attributes databaseName and

factoryClassName.

capped boolean Enable support for capped

collections

collectionSize int Specify the size in bytes of the

capped collection to use if enabled.

The minimum size is 4096 bytes,

and larger sizes will be increased

to the nearest integer multiple of

256. See the capped collection

documentation linked above for

more information.

MongoDB2 Provider Parameters

This appender is MapMessage-aware.

Here are a few sample configurations for the NoSQLAppender and MongoDB2 provider:

<?xml version="1.0" encoding="UTF-8"?>

<MongoDb2 databaseName="applicationDb" collectionName="applicationLog" server="mongo.example.org"

username="loggingUser" password="abc123" />

</NoSql>

</Appenders>

</Root>

</Loggers>

</Configuration>

9 Appenders 123

<?xml version="1.0" encoding="UTF-8"?>

<MongoDb2 collectionName="applicationLog" factoryClassName="org.example.db.ConnectionFactory"

factoryMethodName="getNewMongoClient" />

</NoSql>

</Appenders>

</Root>

</Loggers>

</Configuration>

Starting in Log4j version 2.11.0, the provider element name is MongoDb2. The name MongoDb is now

a deprecated alias for MongoDb2.

9.1.16 NoSQLAppender for MongoDB 3

This section details specializations of the NoSQLAppender provider for MongoDB using the

MongoDB driver version 3. The NoSQLAppender Appender writes log events to a NoSQL database

using an internal lightweight provider interface.

Parameter Name Type Description

collectionName String Required. The name of the

MongoDB collection to insert the

events into.

writeConcernConstant Field By default, the MongoDB provider

inserts records with the instructions

com.mongodb.WriteConcern.ACKNOWLEDGED.

Use this optional attribute to specify

the name of a constant other than

ACKNOWLEDGED.

writeConcernConstantClass Class If you specify

writeConcernConstant,

you can use this attribute to

specify a class other than

com.mongodb.WriteConcern

to find the constant on (to create

your own custom instructions).

9 Appenders 124

factoryClassName Class To provide a connection to

the MongoDB database, you

can use this attribute and

factoryMethodName

to specify a class and static

method to get the connection

from. The method must return a

com.mongodb.client.MongoDatabase

or a

com.mongodb.MongoClient.

If the

com.mongodb.client.MongoDatabase

is not authenticated, you must

also specify a username and

password. If you use the

factory method for providing a

connection, you must not specify

the databaseName, server, or

port attributes.

factoryMethodName Method See the documentation for attribute

factoryClassName.

databaseName String If you do not specify a

factoryClassName and

factoryMethodName for

providing a MongoDB connection,

you must specify a MongoDB

database name using this

attribute. You must also specify

a username and password.

You can optionally also specify a

server (defaults to localhost),

and a port (defaults to the default

MongoDB port).

server String See the documentation for attribute

databaseName.

port int See the documentation for attribute

databaseName.

username String See the documentation for

attributes databaseName and

factoryClassName.

password String See the documentation for

attributes databaseName and

factoryClassName.

capped boolean Enable support for capped

collections

collectionSize int Specify the size in bytes of the

capped collection to use if enabled.

The minimum size is 4096 bytes,

and larger sizes will be increased

to the nearest integer multiple of

256. See the capped collection

documentation linked above for

more information.

9 Appenders 125

MongoDB3 Provider Parameters

This appender is MapMessage-aware.

Here are a few sample configurations for the NoSQLAppender and MongoDB3 provider:

<?xml version="1.0" encoding="UTF-8"?>

<MongoDb3 databaseName="applicationDb" collectionName="applicationLog" server="mongo.example.org"

username="loggingUser" password="abc123" />

</NoSql>

</Appenders>

</Root>

</Loggers>

</Configuration>

<?xml version="1.0" encoding="UTF-8"?>

<MongoDb3 collectionName="applicationLog" factoryClassName="org.example.db.ConnectionFactory"

factoryMethodName="getNewMongoClient" />

</NoSql>

</Appenders>

</Root>

</Loggers>

</Configuration>

9.1.17 NoSQLAppender for Apache CouchDB

This section details specializations of the NoSQLAppender provider for CouchDB. The

NoSQLAppender writes log events to a NoSQL database using an internal lightweight provider

interface.

Parameter Name Type Description

9 Appenders 126

factoryClassName Class To provide a connection to

the CouchDB database, you

can use this attribute and

factoryMethodName

to specify a class and static

method to get the connection

from. The method must return a

org.lightcouch.CouchDbClient

or a

org.lightcouch.CouchDbProperties.

If you use the factory method for

providing a connection, you must

not specify the databaseName,

protocol, server, port,

username, or password

attributes.

factoryMethodName Method See the documentation for attribute

factoryClassName.

databaseName String If you do not specify a

factoryClassName and

factoryMethodName for

providing a CouchDB connection,

you must specify a CouchDB

database name using this

attribute. You must also specify

a username and password.

You can optionally also specify

a protocol (defaults to http),

server (defaults to localhost),

and a port (defaults to 80 for http

and 443 for https).

protocol String Must either be "http" or "https."

See the documentation for attribute

databaseName.

server String See the documentation for attribute

databaseName.

port int See the documentation for attribute

databaseName.

username String See the documentation for

attributes databaseName.

password String See the documentation for

attributes databaseName.

CouchDB Provider Parameters

Here are a few sample configurations for the NoSQLAppender and CouchDB provider:

9 Appenders 127

<?xml version="1.0" encoding="UTF-8"?>

<CouchDb databaseName="applicationDb" protocol="https" server="couch.example.org"

username="loggingUser" password="abc123" />

</NoSql>

</Appenders>

</Root>

</Loggers>

</Configuration>

9.1.18 OutputStreamAppender

The OutputStreamAppender provides the base for many of the other Appenders such as the File

and Socket appenders that write the event to an Output Stream. It cannot be directly configured.

Support for immediateFlush and buffering is provided by the OutputStreamAppender. The

OutputStreamAppender uses an OutputStreamManager to handle the actual I/O, allowing the stream

to be shared by Appenders in multiple configurations.

9.1.19 RandomAccessFileAppender

The RandomAccessFileAppender is similar to the standard FileAppender except it is always

buffered (this cannot be switched off) and internally it uses a ByteBuffer + RandomAccessFile

instead of a BufferedOutputStream. We saw a 20-200% performance improvement compared

to FileAppender with "bufferedIO=true" in our measurements. Similar to the FileAppender,

RandomAccessFileAppender uses a RandomAccessFileManager to actually perform the file

I/O. While RandomAccessFileAppender from different Configurations cannot be shared, the

RandomAccessFileManagers can be if the Manager is accessible. For example, two web applications

in a servlet container can have their own configuration and safely write to the same file if Log4j is in a

ClassLoader that is common to both of them.

Parameter Name Type Description

append boolean When true - the default, records

will be appended to the end of the

file. When set to false, the file will

be cleared before new records are

written.

fileName String The name of the file to write to.

If the file, or any of its parent

directories, do not exist, they will be

created.

filters Filter A Filter to determine if the

event should be handled by

this Appender. More than one

Filter may be used by using a

CompositeFilter.

9 Appenders 128

immediateFlush boolean When set to true - the default,

each write will be followed by

a flush. This will guarantee the

data is written to disk but could

impact performance.

Flushing after every write is

only useful when using this

appender with synchronous

loggers. Asynchronous

loggers and appenders will

automatically flush at the end

of a batch of events, even if

immediateFlush is set to false.

This also guarantees the data

is written to disk but is more

efficient.

bufferSize int The buffer size, defaults to 262,144

bytes (256 * 1024).

layout Layout The Layout to use to format the

LogEvent. If no layout is supplied

the default pattern layout of "%m

%n" will be used.

name String The name of the Appender.

ignoreExceptions boolean The default is true, causing

exceptions encountered while

appending events to be internally

logged and then ignored. When

set to false exceptions will be

propagated to the caller, instead.

You must set this to false when

wrapping this Appender in a

FailoverAppender.

RandomAccessFileAppender Parameters

Here is a sample RandomAccessFile configuration:

<?xml version="1.0" encoding="UTF-8"?>

</PatternLayout>

</RandomAccessFile>

</Appenders>

</Root>

</Loggers>

</Configuration>

9 Appenders 129

9.1.20 RewriteAppender

The RewriteAppender allows the LogEvent to manipulated before it is processed by another

Appender. This can be used to mask sensitive information such as passwords or to inject

information into each event. The RewriteAppender must be configured with a RewritePolicy. The

RewriteAppender should be configured after any Appenders it references to allow it to shut down

properly.

Parameter Name Type Description

AppenderRef String The name of the Appenders to

call after the LogEvent has been

manipulated. Multiple AppenderRef

elements can be configured.

filter Filter A Filter to determine if the

event should be handled by

this Appender. More than one

Filter may be used by using a

CompositeFilter.

name String The name of the Appender.

rewritePolicy RewritePolicy The RewritePolicy that will

manipulate the LogEvent.

ignoreExceptions boolean The default is true, causing

exceptions encountered while

appending events to be internally

logged and then ignored. When

set to false exceptions will be

propagated to the caller, instead.

You must set this to false when

wrapping this Appender in a

FailoverAppender.

RewriteAppender Parameters

9.1.20.1 RewritePolicy

RewritePolicy is an interface that allows implementations to inspect and possibly modify LogEvents

before they are passed to Appender. RewritePolicy declares a single method named rewrite that must

be implemented. The method is passed the LogEvent and can return the same event or create a new

one.

9.MapRewritePolicy

MapRewritePolicy will evaluate LogEvents that contain a MapMessage and will add or update

elements of the Map.

Parameter Name Type Description

mode String "Add" or "Update"

keyValuePair KeyValuePair[] An array of keys and their values.

The following configuration shows a RewriteAppender configured to add a product key and its value

to the MapMessage.:

9 Appenders 130

<?xml version="1.0" encoding="UTF-8"?>

</Console>

</MapRewritePolicy>

</Rewrite>

</Appenders>

</Root>

</Loggers>

</Configuration>

9.PropertiesRewritePolicy

PropertiesRewritePolicy will add properties configured on the policy to the ThreadContext Map being

logged. The properties will not be added to the actual ThreadContext Map. The property values may

contain variables that will be evaluated when the configuration is processed as well as when the event

is logged.

Parameter Name Type Description

properties Property[] One of more Property elements to

define the keys and values to be

added to the ThreadContext Map.

The following configuration shows a RewriteAppender configured to add a product key and its value

to the MapMessage:

9 Appenders 131

<?xml version="1.0" encoding="UTF-8"?>

</Console>

<Property name="env">${sys:environment}</Property>

</PropertiesRewritePolicy>

</Rewrite>

</Appenders>

</Root>

</Loggers>

</Configuration>

9.LoggerNameLevelRewritePolicy

You can use this policy to make loggers in third party code less chatty by changing event levels. The

LoggerNameLevelRewritePolicy will rewrite log event levels for a given logger name prefix. You

configure a LoggerNameLevelRewritePolicy with a logger name prefix and a pairs of levels, where a

pair defines a source level and a target level.

Parameter Name Type Description

logger String A logger name used as a prefix to

test each event's logger name.

LevelPair KeyValuePair[] An array of keys and their values,

each key is a source level, each

value a target level.

The following configuration shows a RewriteAppender configured to map level INFO to DEBUG and

level WARN to INFO for all loggers that start with com.foo.bar.

9 Appenders 132

<?xml version="1.0" encoding="UTF-8"?>

</Console>

</LoggerNameLevelRewritePolicy>

</Rewrite>

</Appenders>

</Root>

</Loggers>

</Configuration>

9.1.21 RollingFileAppender

The RollingFileAppender is an OutputStreamAppender that writes to the File named in the fileName

parameter and rolls the file over according the TriggeringPolicy and the RolloverPolicy. The

RollingFileAppender uses a RollingFileManager (which extends OutputStreamManager) to

actually perform the file I/O and perform the rollover. While RolloverFileAppenders from different

Configurations cannot be shared, the RollingFileManagers can be if the Manager is accessible. For

example, two web applications in a servlet container can have their own configuration and safely

write to the same file if Log4j is in a ClassLoader that is common to both of them.

A RollingFileAppender requires a TriggeringPolicy and a RolloverStrategy. The triggering

policy determines if a rollover should be performed while the RolloverStrategy defines how

the rollover should be done. If no RolloverStrategy is configured, RollingFileAppender will

use the DefaultRolloverStrategy. Since log4j-2.5, a custom delete action can be configured

in the DefaultRolloverStrategy to run at rollover. Since 2.8 if no file name is configured then

DirectWriteRolloverStrategy will be used instead of DefaultRolloverStrategy. Since log4j-2.9, a

custom POSIX file attribute view action can be configured in the DefaultRolloverStrategy to run at

rollover, if not defined, inherited POSIX file attribute view from the RollingFileAppender will be

applied.

File locking is not supported by the RollingFileAppender.

Parameter Name Type Description

append boolean When true - the default, records

will be appended to the end of the

file. When set to false, the file will

be cleared before new records are

written.

9 Appenders 133

bufferedIO boolean When true - the default, records

will be written to a buffer and the

data will be written to disk when the

buffer is full or, if immediateFlush

is set, when the record is written.

File locking cannot be used with

bufferedIO. Performance tests

have shown that using buffered I/O

significantly improves performance,

even if immediateFlush is enabled.

bufferSize int When bufferedIO is true, this is

the buffer size, the default is 8192

bytes.

createOnDemand boolean The appender creates the file

on-demand. The appender only

creates the file when a log event

passes all filters and is routed to

this appender. Defaults to false.

filter Filter A Filter to determine if the

event should be handled by

this Appender. More than one

Filter may be used by using a

CompositeFilter.

fileName String The name of the file to write to.

If the file, or any of its parent

directories, do not exist, they will be

created.

filePattern String The pattern of the file name of

the archived log file. The format

of the pattern is dependent on

the RolloverPolicy that is used.

The DefaultRolloverPolicy will

accept both a date/time pattern

compatible with SimpleDateFormat

and/or a %i which represents an

integer counter. The pattern also

supports interpolation at runtime so

any of the Lookups (such as the

DateLookup) can be included in the

pattern.

9 Appenders 134

immediateFlush boolean When set to true - the default,

each write will be followed by

a flush. This will guarantee the

data is written to disk but could

impact performance.

Flushing after every write is

only useful when using this

appender with synchronous

loggers. Asynchronous

loggers and appenders will

automatically flush at the end

of a batch of events, even if

immediateFlush is set to false.

This also guarantees the data

is written to disk but is more

efficient.

layout Layout The Layout to use to format the

LogEvent. If no layout is supplied

the default pattern layout of "%m

%n" will be used.

name String The name of the Appender.

policy TriggeringPolicy The policy to use to determine if a

rollover should occur.

strategy RolloverStrategy The strategy to use to determine

the name and location of the

archive file.

ignoreExceptions boolean The default is true, causing

exceptions encountered while

appending events to be internally

logged and then ignored. When

set to false exceptions will be

propagated to the caller, instead.

You must set this to false when

wrapping this Appender in a

FailoverAppender.

filePermissions String File attribute permissions

in POSIX format to apply

whenever the file is created.

Underlying files system shall

support POSIX file attribute

view.

Examples: rw------- or rw-rw-

rw- etc...

9 Appenders 135

fileOwner String File owner to define whenever

the file is created.

Changing file's owner may be

restricted for security reason

and Operation not permitted

IOException thrown. Only

processes with an effective

user ID equal to the user ID

of the file or with appropriate

privileges may change

the ownership of a file if

_POSIX_CHOWN_RESTRICTED

is in effect for path.

Underlying files system shall

support file owner attribute

view.

fileGroup String File group to define whenever

the file is created.

Underlying files system shall

support POSIX file attribute

view.

RollingFileAppender Parameters

9.1.21.1 Triggering Policies

9.Composite Triggering Policy

The CompositeTriggeringPolicy combines multiple triggering policies and returns true if any

of the configured policies return true. The CompositeTriggeringPolicy is configured simply by

wrapping other policies in a Policies element.

For example, the following XML fragment defines policies that rollover the log when the JVM starts,

when the log size reaches twenty megabytes, and when the current date no longer matches the log’s

start date.

</Policies>

9.Cron Triggering Policy

The CronTriggeringPolicy triggers rollover based on a cron expression.

Parameter Name Type Description

9 Appenders 136

schedule String The cron expression. The

expression is the same as what is

allowed in the Quartz scheduler.

See CronExpression for a full

description of the expression.

evaluateOnStartup boolean On startup the cron expression

will be evaluated against the file's

last modification timestamp. If the

cron expression indicates a rollover

should have occurred between that

time and the current time the file

will be immediately rolled over.

CronTriggeringPolicy Parameters

9.OnStartup Triggering Policy

The OnStartupTriggeringPolicy policy causes a rollover if the log file is older than the current

JVM's start time and the minimum file size is met or exceeded.

Parameter Name Type Description

minSize long The minimum size the file must

have to roll over. A size of zero will

cause a roll over no matter what

the file size is. The default value is

1, which will prevent rolling over an

empty file.

OnStartupTriggeringPolicy Parameters

Google App Engine note:

When running in Google App Engine, the OnStartup policy causes a rollover if

the log file is older than the time when Log4J initialized. (Google App Engine

restricts access to certain classes so Log4J cannot determine JVM start time with

java.lang.management.ManagementFactory.getRuntimeMXBean().getStartTime() and

falls back to Log4J initialization time instead.)

9.SizeBased Triggering Policy

The SizeBasedTriggeringPolicy causes a rollover once the file has reached the specified size.

The size can be specified in bytes, with the suffix KB, MB or GB, for example 20MB.

9.TimeBased Triggering Policy

The TimeBasedTriggeringPolicy causes a rollover once the date/time pattern no longer applies

to the active file. This policy accepts an interval attribute which indicates how frequently the

rollover should occur based on the time pattern and a modulate boolean attribute.

Parameter Name Type Description

9 Appenders 137

interval integer How often a rollover should

occur based on the most specific

time unit in the date pattern. For

example, with a date pattern with

hours as the most specific item and

and increment of 4 rollovers would

occur every 4 hours. The default

value is 1.

modulate boolean Indicates whether the interval

should be adjusted to cause the

next rollover to occur on the interval

boundary. For example, if the item

is hours, the current hour is 3 am

and the interval is 4 then the first

rollover will occur at 4 am and then

next ones will occur at 8 am, noon,

4pm, etc.

maxRandomDelay integer Indicates the maximum number

of seconds to randomly delay a

rollover. By default, this is 0 which

indicates no delay. This setting is

useful on servers where multiple

applications are configured to

rollover log files at the same time

and can spread the load of doing

so across time.

TimeBasedTriggeringPolicy Parameters

9.1.21.2 Rollover Strategies

9.Default Rollover Strategy

The default rollover strategy accepts both a date/time pattern and an integer from the filePattern

attribute specified on the RollingFileAppender itself. If the date/time pattern is present it will be

replaced with the current date and time values. If the pattern contains an integer it will be incremented

on each rollover. If the pattern contains both a date/time and integer in the pattern the integer will

be incremented until the result of the date/time pattern changes. If the file pattern ends with ".gz",

".zip", ".bz2", ".deflate", ".pack200", or ".xz" the resulting archive will be compressed using the

compression scheme that matches the suffix. The formats bzip2, Deflate, Pack200 and XZ require

Apache Commons Compress. In addition, XZ requires XZ for Java. The pattern may also contain

lookup references that can be resolved at runtime such as is shown in the example below.

The default rollover strategy supports three variations for incrementing the counter. The first is the

"fixed window" strategy. To illustrate how it works, suppose that the min attribute is set to 1, the max

attribute is set to 3, the file name is "foo.log", and the file name pattern is "foo-%i.log".

Number of rollovers Active output target Archived log files Description

0 foo.log - All logging is going to the

initial file.

9 Appenders 138

1 foo.log foo-1.log During the first rollover

foo.log is renamed to

foo-1.log. A new foo.log

file is created and starts

being written to.

2 foo.log foo-1.log, foo-2.log During the second rollover

foo-1.log is renamed to

foo-2.log and foo.log is

renamed to foo-1.log. A

new foo.log file is created

and starts being written

to.

3 foo.log foo-1.log, foo-2.log,

foo-3.log During the third rollover

foo-2.log is renamed to

foo-3.log, foo-1.log is

renamed to foo-2.log and

foo.log is renamed to

foo-1.log. A new foo.log

file is created and starts

being written to.

4 foo.log foo-1.log, foo-2.log,

foo-3.log In the fourth and

subsequent rollovers,

foo-3.log is deleted,

foo-2.log is renamed to

foo-3.log, foo-1.log is

renamed to foo-2.log and

foo.log is renamed to

foo-1.log. A new foo.log

file is created and starts

being written to.

By way of contrast, when the fileIndex attribute is set to "max" but all the other settings are the same

the following actions will be performed.

Number of rollovers Active output target Archived log files Description

0 foo.log - All logging is going to the

initial file.

1 foo.log foo-1.log During the first rollover

foo.log is renamed to

foo-1.log. A new foo.log

file is created and starts

being written to.

2 foo.log foo-1.log, foo-2.log During the second rollover

foo.log is renamed to

foo-2.log. A new foo.log

file is created and starts

being written to.

3 foo.log foo-1.log, foo-2.log,

foo-3.log During the third rollover

foo.log is renamed to

foo-3.log. A new foo.log

file is created and starts

being written to.

9 Appenders 139

4 foo.log foo-1.log, foo-2.log,

foo-3.log In the fourth and

subsequent rollovers,

foo-1.log is deleted,

foo-2.log is renamed to

foo-1.log, foo-3.log is

renamed to foo-2.log and

foo.log is renamed to

foo-3.log. A new foo.log

file is created and starts

being written to.

Finally, as of release 2.8, if the fileIndex attribute is set to "nomax" then the min and max values

will be ignored and file numbering will increment by 1 and each rollover will have an incrementally

higher value with no maximum number of files.

Parameter Name Type Description

fileIndex String If set to "max" (the default), files

with a higher index will be newer

than files with a smaller index.

If set to "min", file renaming and

the counter will follow the Fixed

Window strategy described above.

min integer The minimum value of the counter.

The default value is 1.

max integer The maximum value of the counter.

Once this values is reached

older archives will be deleted on

subsequent rollovers. The default

value is 7.

compressionLevel integer Sets the compression level, 0-9,

where 0 = none, 1 = best speed,

through 9 = best compression. Only

implemented for ZIP files.

tempCompressedFilePattern String The pattern of the file name

of the archived log file during

compression.

DefaultRolloverStrategy Parameters

9.DirectWrite Rollover Strategy

The DirectWriteRolloverStrategy causes log events to be written directly to files represented by the

file pattern. With this strategy file renames are not performed. If the size-based triggering policy

causes multiple files to be written durring the specified time period they will be numbered starting at

one and continually incremented until a time-based rollover occurs.

Warning: If the file pattern has a suffix indicating compression should take place the current file will

not be compressed when the application is shut down. Furthermore, if the time changes such that the

file pattern no longer matches the current file it will not be compressed at startup either.

Parameter Name Type Description

9 Appenders 140

maxFiles String The maximum number of files to

allow in the time period matching

the file pattern. If the number of

files is exceeded the oldest file will

be deleted. If specified, the value

must be greater than 1. If the value

is less than zero or omitted then the

number of files will not be limited.

compressionLevel integer Sets the compression level, 0-9,

where 0 = none, 1 = best speed,

through 9 = best compression. Only

implemented for ZIP files.

tempCompressedFilePattern String The pattern of the file name

of the archived log file during

compression.

DirectWriteRolloverStrategy Parameters

Below is a sample configuration that uses a RollingFileAppender with both the time and size based

triggering policies, will create up to 7 archives on the same day (1-7) that are stored in a directory

based on the current year and month, and will compress each archive using gzip:

<?xml version="1.0" encoding="UTF-8"?>

<RollingFile name="RollingFile" fileName="logs/app.log"

filePattern="logs/$${date:yyyy-MM}/app-%d{MM-dd-yyyy}-%i.log.gz">

</PatternLayout>

</Policies>

</RollingFile>

</Appenders>

</Root>

</Loggers>

</Configuration>

This second example shows a rollover strategy that will keep up to 20 files before removing them.

9 Appenders 141

<?xml version="1.0" encoding="UTF-8"?>

<RollingFile name="RollingFile" fileName="logs/app.log"

filePattern="logs/$${date:yyyy-MM}/app-%d{MM-dd-yyyy}-%i.log.gz">

</PatternLayout>

</Policies>

</RollingFile>

</Appenders>

</Root>

</Loggers>

</Configuration>

Below is a sample configuration that uses a RollingFileAppender with both the time and size based

triggering policies, will create up to 7 archives on the same day (1-7) that are stored in a directory

based on the current year and month, and will compress each archive using gzip and will roll every 6

hours when the hour is divisible by 6:

<?xml version="1.0" encoding="UTF-8"?>

<RollingFile name="RollingFile" fileName="logs/app.log"

filePattern="logs/$${date:yyyy-MM}/app-%d{yyyy-MM-dd-HH}-%i.log.gz">

</PatternLayout>

</Policies>

</RollingFile>

</Appenders>

</Root>

</Loggers>

</Configuration>

This sample configuration uses a RollingFileAppender with both the cron and size based triggering

policies, and writes directly to an unlimited number of archive files. The cron trigger causes a rollover

every hour while the file size is limited to 250MB:

9 Appenders 142

<?xml version="1.0" encoding="UTF-8"?>

</PatternLayout>

</Policies>

</RollingFile>

</Appenders>

</Root>

</Loggers>

</Configuration>

This sample configuration is the same as the previous but limits the number of files saved each hour

to 10:

<?xml version="1.0" encoding="UTF-8"?>

</PatternLayout>

</Policies>

</RollingFile>

</Appenders>

</Root>

</Loggers>

</Configuration>

9.Log Archive Retention Policy: Delete on Rollover

Log4j-2.5 introduces a Delete action that gives users more control over what files are deleted at

rollover time than what was possible with the DefaultRolloverStrategy max attribute. The Delete

action lets users configure one or more conditions that select the files to delete relative to a base

directory.

Note that it is possible to delete any file, not just rolled over log files, so use this action with care!

With the testMode parameter you can test your configuration without accidentally deleting the

wrong files.

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Parameter Name Type Description

basePath String Required. Base path from where to

start scanning for files to delete.

maxDepth int The maximum number of levels

of directories to visit. A value of 0

means that only the starting file (the

base path itself) is visited, unless

denied by the security manager.

A value of Integer.MAX_VALUE

indicates that all levels should be

visited. The default is 1, meaning

only the files in the specified base

directory.

followLinks boolean Whether to follow symbolic links.

Default is false.

testMode boolean If true, files are not deleted but

instead a message is printed to

the status logger at INFO level.

Use this to do a dry run to test if the

configuration works as expected.

Default is false.

pathSorter PathSorter A plugin implementing the

PathSorter interface to sort the files

before selecting the files to delete.

The default is to sort most recently

modified files first.

9 Appenders 144

pathConditions PathCondition[] Required if no ScriptCondition

is specified. One or more

PathCondition elements.

If more than one condition

is specified, they all need

to accept a path before it is

deleted. Conditions can be

nested, in which case the inner

condition(s) are evaluated only

if the outer condition accepts

the path. If conditions are not

nested they may be evaluated in

any order.

Conditions can also be

combined with the logical

operators AND, OR and NOT

by using the IfAll, IfAny and

IfNot composite conditions.

Users can create custom

conditions or use the built-in

conditions:

•IfFileName - accepts files

whose path (relative to the

base path) matches a regular

expression or a glob.

•IfLastModified - accepts files

that are as old as or older than

the specified duration.

•IfAccumulatedFileCount -

accepts paths after some

count threshold is exceeded

during the file tree walk.

•IfAccumulatedFileSize -

accepts paths after the

accumulated file size threshold

is exceeded during the file tree

walk.

• IfAll - accepts a path if all

nested conditions accept

it (logical AND). Nested

conditions may be evaluated in

any order.

• IfAny - accepts a path if one of

the nested conditions accept it

(logical OR). Nested conditions

may be evaluated in any order.

• IfNot - accepts a path if the

nested condition does not

accept it (logical NOT).

9 Appenders 145

scriptCondition ScriptCondition Required if no PathConditions

are specified. A

ScriptCondition element

specifying a script.

The ScriptCondition should

contain a Script, ScriptRef or

ScriptFile element that specifies

the logic to be executed.

(See also the ScriptFilter

documentation for more

examples of configuring

ScriptFiles and ScriptRefs.)

The script is passed a number of

parameters, including a list of

paths found under the base path

(up to maxDepth) and must

return a list with the paths to

delete.

Delete Parameters

Parameter Name Type Description

glob String Required if regex not specified.

Matches the relative path (relative

to the base path) using a limited

pattern language that resembles

regular expressions but with a

simpler syntax.

regex String Required if glob not specified.

Matches the relative path (relative

to the base path) using a regular

expression as defined by the

Pattern class.

nestedConditions PathCondition[] An optional set of nested

PathConditions. If any nested

conditions exist they all need

to accept the file before it is

deleted. Nested conditions are only

evaluated if the outer condition

accepts a file (if the path name

matches).

IfFileName Condition Parameters

Parameter Name Type Description

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age String Required. Specifies a duration.

The condition accepts files that are

as old or older than the specified

duration.

nestedConditions PathCondition[] An optional set of nested

PathConditions. If any nested

conditions exist they all need

to accept the file before it is

deleted. Nested conditions are only

evaluated if the outer condition

accepts a file (if the file is old

enough).

IfLastModified Condition Parameters

Parameter Name Type Description

exceeds int Required. The threshold count from

which files will be deleted.

nestedConditions PathCondition[] An optional set of nested

PathConditions. If any nested

conditions exist they all need

to accept the file before it is

deleted. Nested conditions are only

evaluated if the outer condition

accepts a file (if the threshold count

has been exceeded).

IfAccumulatedFileCount Condition Parameters

Parameter Name Type Description

exceeds String Required. The threshold

accumulated file size from which

files will be deleted. The size can

be specified in bytes, with the suffix

KB, MB or GB, for example 20MB.

nestedConditions PathCondition[] An optional set of nested

PathConditions. If any nested

conditions exist they all need

to accept the file before it is

deleted. Nested conditions are only

evaluated if the outer condition

accepts a file (if the threshold

accumulated file size has been

exceeded).

IfAccumulatedFileSize Condition Parameters

Below is a sample configuration that uses a RollingFileAppender with the cron triggering policy

configured to trigger every day at midnight. Archives are stored in a directory based on the current

9 Appenders 147

year and month. All files under the base directory that match the "*/app-*.log.gz" glob and are 60

days old or older are deleted at rollover time.

<?xml version="1.0" encoding="UTF-8"?>

</Properties>

<RollingFile name="RollingFile" fileName="${baseDir}/app.log"

filePattern="${baseDir}/$${date:yyyy-MM}/app-%d{yyyy-MM-dd}.log.gz">

</Delete>

</DefaultRolloverStrategy>

</RollingFile>

</Appenders>

</Root>

</Loggers>

</Configuration>

Below is a sample configuration that uses a RollingFileAppender with both the time and size based

triggering policies, will create up to 100 archives on the same day (1-100) that are stored in a

directory based on the current year and month, and will compress each archive using gzip and will

roll every hour. During every rollover, this configuration will delete files that match "*/app-*.log.gz"

and are 30 days old or older, but keep the most recent 100 GB or the most recent 10 files, whichever

comes first.

9 Appenders 148

<?xml version="1.0" encoding="UTF-8"?>

</Properties>

<RollingFile name="RollingFile" fileName="${baseDir}/app.log"

filePattern="${baseDir}/$${date:yyyy-MM}/app-%d{yyyy-MM-dd-HH}-%i.log.gz">

</Policies>

<!--

Nested conditions: the inner condition is only evaluated on files

for which the outer conditions are true.

-->

<IfAny>

</IfAny>

</IfLastModified>

</IfFileName>

</Delete>

</DefaultRolloverStrategy>

</RollingFile>

</Appenders>

</Root>

</Loggers>

</Configuration>

Parameter Name Type Description

script Script, ScriptFile or ScriptRef The Script element that specifies

the logic to be executed. The

script is passed a list of paths

found under the base path and

must return the paths to delete

as a java.util.List<

PathWithAttributes>. See

also the ScriptFilter documentation

for an example of how ScriptFiles

and ScriptRefs can be configured.

ScriptCondition Parameters

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Parameter Name Type Description

basePath java.nio.file.Path The directory from where the

Delete action started scanning

for files to delete. Can be used to

relativize the paths in the pathList.

pathList java.util.List<

PathWithAttributes>

The list of paths found under the

base path up to the specified

max depth, sorted most recently

modified files first. The script is free

to modify and return this list.

statusLogger StatusLogger The StatusLogger that can be used

to log internal events during script

execution.

configuration Configuration The Configuration that owns this

ScriptCondition.

substitutor StrSubstitutor The StrSubstitutor used to replace

lookup variables.

? String Any properties declared in the

configuration.

Script Parameters

Below is a sample configuration that uses a RollingFileAppender with the cron triggering policy

configured to trigger every day at midnight. Archives are stored in a directory based on the current

year and month. The script returns a list of rolled over files under the base directory dated Friday the

13th. The Delete action will delete all files returned by the script.

9 Appenders 150

<?xml version="1.0" encoding="UTF-8"?>

</Properties>

<RollingFile name="RollingFile" fileName="${baseDir}/app.log"

filePattern="${baseDir}/$${date:yyyy-MM}/app-%d{yyyyMMdd}.log.gz">

<Script name="superstitious" language="groovy"><![CDATA[

import java.nio.file.*;

def result = [];

def pattern = ~/\d*\/app-(\d*)\.log\.gz/;

pathList.each { pathWithAttributes ->

def relative = basePath.relativize pathWithAttributes.path

statusLogger.trace 'SCRIPT: relative path=' + relative + " (base=$basePath)";

// remove files dated Friday the 13th

def matcher = pattern.matcher(relative.toString());

if (matcher.find()) {

def dateString = matcher.group(1);

def calendar = Date.parse("yyyyMMdd", dateString).toCalendar();

def friday13th = calendar.get(Calendar.DAY_OF_MONTH) == 13 \

&& calendar.get(Calendar.DAY_OF_WEEK) == Calendar.FRIDAY;

if (friday13th) {

result.add pathWithAttributes;

statusLogger.trace 'SCRIPT: deleting path ' + pathWithAttributes;

}

statusLogger.trace 'SCRIPT: returning ' + result;

result;

]] >

</Script>

</ScriptCondition>

</Delete>

</DefaultRolloverStrategy>

</RollingFile>

</Appenders>

</Root>

</Loggers>

</Configuration>

9 Appenders 151

9.Log Archive File Attribute View Policy: Custom file attribute on Rollover

Log4j-2.9 introduces a PosixViewAttribute action that gives users more control over which file

attribute permissions, owner and group should be applied. The PosixViewAttribute action lets users

configure one or more conditions that select the eligible files relative to a base directory.

Parameter Name Type Description

basePath String Required. Base path from where

to start scanning for files to apply

attributes.

maxDepth int The maximum number of levels

of directories to visit. A value of 0

means that only the starting file (the

base path itself) is visited, unless

denied by the security manager.

A value of Integer.MAX_VALUE

indicates that all levels should be

visited. The default is 1, meaning

only the files in the specified base

directory.

followLinks boolean Whether to follow symbolic links.

Default is false.

pathConditions PathCondition[] see DeletePathCondition

filePermissions String File attribute permissions in

POSIX format to apply when

action is executed.

Underlying files system shall

support POSIX file attribute

view.

Examples: rw------- or rw-rw-

rw- etc...

fileOwner String File owner to define when

action is executed.

Changing file's owner may be

restricted for security reason

and Operation not permitted

IOException thrown. Only

processes with an effective

user ID equal to the user ID

of the file or with appropriate

privileges may change

the ownership of a file if

_POSIX_CHOWN_RESTRICTED

is in effect for path.

Underlying files system shall

support file owner attribute

view.

9 Appenders 152

fileGroup String File group to define whene

action is executed.

Underlying files system shall

support POSIX file attribute

view.

PosixViewAttribute Parameters

Below is a sample configuration that uses a RollingFileAppender and defines different POSIX file

attribute view for current and rolled log files.

<?xml version="1.0" encoding="UTF-8"?>

</Properties>

<RollingFile name="RollingFile" fileName="${baseDir}/app.log"

filePattern="${baseDir}/$${date:yyyy-MM}/app-%d{yyyyMMdd}.log.gz"

filePermissions="rw-------">

</PosixViewAttribute>

</DefaultRolloverStrategy>

</RollingFile>

</Appenders>

</Root>

</Loggers>

</Configuration>

9.1.22 RollingRandomAccessFileAppender

The RollingRandomAccessFileAppender is similar to the standard RollingFileAppender except

it is always buffered (this cannot be switched off) and internally it uses a ByteBuffer +

RandomAccessFile instead of a BufferedOutputStream. We saw a 20-200% performance

improvement compared to RollingFileAppender with "bufferedIO=true" in our measurements. The

RollingRandomAccessFileAppender writes to the File named in the fileName parameter and rolls the

file over according the TriggeringPolicy and the RolloverPolicy. Similar to the RollingFileAppender,

RollingRandomAccessFileAppender uses a RollingRandomAccessFileManager to actually perform

the file I/O and perform the rollover. While RollingRandomAccessFileAppender from different

Configurations cannot be shared, the RollingRandomAccessFileManagers can be if the Manager is

accessible. For example, two web applications in a servlet container can have their own configuration

and safely write to the same file if Log4j is in a ClassLoader that is common to both of them.

9 Appenders 153

A RollingRandomAccessFileAppender requires a TriggeringPolicy and a