Hibernate Quick Guide

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HIBERNATE QUICK GUIDE
http://www.tuto rialspo int.co m/hibe rnate /hibe rnate _quick_g uide .htm

Co pyrig ht © tuto rials po int.co m

Hibernate is an Object-Relational Mapping (ORM) solution for JAVA and it raised as an open source persistent
framework created by Gavin King in 2001. It is a powerful, hig h performance Object-Relational Persistence and
Query service for any Java Application.
Hibernate maps Java classes to database tables and from Java data types to SQL data types and relieve the
developer from 95% of common data persistence related prog ramming tasks.
Hibernate sits between traditional Java objects and database server to handle all the work in persisting those
objects based on the appropriate O/R mechanisms and patterns.

Hibernate Advantag es:
Hibernate takes care of mapping Java classes to database tables using XML files and without writing any
line of code.
Provides simple APIs for storing and retrieving Java objects directly to and from the database.
If there is chang e in Database or in any table then the only need to chang e XML file properties.
Abstract away the unfamiliar SQL types and provide us to work around familiar Java Objects.
Hibernate does not require an application server to operate.
Manipulates Complex associations of objects of your database.
Minimize database access with smart fetching strateg ies.
Provides Simple querying of data.

Supported Databases:
Hibernate supports almost all the major RDBMS. Following is list of few of the database eng ines supported by
Hibernate.
HSQL Database Eng ine
DB2/NT
MySQL
Postg reSQL
FrontBase
Oracle
Microsoft SQL Server Database
Sybase SQL Server

Informix Dynamic Server

Hibernate Architecture:
T he Hibernate architecture is layered to keep you isolated from having to know the underlying APIs. Hibernate
makes use of the database and config uration data to provide persistence services (and persistent objects) to the
application.
Following is a very hig h level view of the Hibernate Application Architecture.

Following is a detailed view of the Hibernate Application Architecture with few important core classes.

Hibernate uses various existing Java APIs, like JDBC, Java T ransaction API(JT A), and Java Naming and
Directory Interface (JNDI). JDBC provides a rudimentary level of abstraction of functionality common to
relational databases, allowing almost any database with a JDBC driver to be supported by Hibernate. JNDI and
JT A allow Hibernate to be integ rated with J2EE application servers.
Following section g ives brief description of each of the class objects involved in Hibernate Application
Architecture.

Config uration Object:
T he Config uration object is the first Hibernate object you create in any Hibernate application and usually created
only once during application initialization. It represents a config uration or properties file required by the
Hibernate. T he Config uration object provides two keys components:
Database Connec tion: T his is handled throug h one or more config uration files supported by
Hibernate. T hese files are hibernate.properties and hibernate.c fg .xml.
Class Mapping Setup
T his component creates the connection between the Java classes and database tables..

SessionFactory Object:
Config uration object is used to create a SessionFactory object which inturn config ures Hibernate for the
application using the supplied config uration file and allows for a Session object to be instantiated. T he
SessionFactory is a thread safe object and used by all the threads of an application.
T he SessionFactory is heavyweig ht object so usually it is created during application start up and kept for later
use. You would need one SessionFactory object per database using a separate config uration file. So if you are
using multiple databases then you would have to create multiple SessionFactory objects.

Session Object:
A Session is used to g et a physical connection with a database. T he Session object is lig htweig ht and desig ned to
be instantiated each time an interaction is needed with the database. Persistent objects are saved and retrieved
throug h a Session object.

T he session objects should not be kept open for a long time because they are not usually thread safe and they
should be created and destroyed them as needed.

Transaction Object:
A T ransaction represents a unit of work with the database and most of the RDBMS supports transaction
functionality. T ransactions in Hibernate are handled by an underlying transaction manag er and transaction (from
JDBC or JT A).
T his is an optional object and Hibernate applications may choose not to use this interface, instead manag ing
transactions in their own application code.

Query Object:
Query objects use SQL or Hibernate Query Lang uag e (HQL) string to retrieve data from the database and
create objects. A Query instance is used to bind query parameters, limit the number of results returned by the
query, and finally to execute the query.

Criteria Object:
Criteria object are used to create and execute object oriented criteria queries to retrieve objects.

Hibernate Environment Setup
T his chapter will explain how to install Hibernate and other associated packag es to prepare a develop
environment for the Hibernate applications. We will work with MySQL database to experiment with Hibernate
examples, so make sure you already have setup for MySQL database. For a more detail on MySQL you can
check our MySQL T utorial.

Downloading Hibernate:
It is assumed that you already have latest version of Java is installed on your machine. Following are the simple
steps to download and install Hibernate on your machine.
Make a choice whether you want to install Hibernate on Windows, or Unix and then proceed to the next
step to download .zip file for windows and .tz file for Unix.
Download the latest version of Hibernate from http://www.hibernate.org /downloads.
At the time of writing this tutorial I downloaded hibernate-distribution-3.6.4.Final and when you
unzip the downloaded file it will g ive you directory structure as follows.

Installing Hibernate:
Once you downloaded and unzipped the latest version of the Hibernate Installation file, you need to perform
following two simple steps. Make sure you are setting your CLASSPAT H variable properly otherwise you will
face problem while compiling your application.
Now copy all the library files from /lib into your CLASSPAT H, and chang e your classpath variable to
include all the JARs:

Finally copy hibernate3.jar file into your CLASSPAT H. T his file lies in the root directory of the
installation and is the primary JAR that Hibernate needs to do its work.

Hibernate Prerequisites:
Following is the list of the packag es/libraries required by Hibernate and you should install them before starting
with Hibernate. T o install these packag es you would have to copy library files from /lib into your CLASSPAT H,
and chang e your CLASSPAT H variable according ly.

S.N.

Pac kag es/Libraries

1

dom4j - XML parsing www.dom4j.org /

2

Xalan - XSLT Processor http://xml.apache.org /xalan-j/

3

Xerc es - T he Xerces Java Parser http://xml.apache.org /xerces-j/

4

c g lib - Appropriate chang es to Java classes at runtime http://cg lib.sourceforg e.net/

5

log 4j - Log g ing Faremwork http://log g ing .apache.org /log 4j

6

Commons - Log g ing , Email etc. http://jakarta.apache.org /commons

7

SLF4J - Log g ing Facade for Java http://www.slf4j.org

Hibernate Config uration
Hibernate requires to know in advance where to find the mapping information that defines how your Java classes
relate to the database tables. Hibernate also requires a set of config uration setting s related to database and
other related parameters. All such information is usually supplied as a standard Java properties file called
hibernate.properties, or as an XML file named hibernate.c fg .xml.
I will consider XML formatted file hibernate.c fg .xml to specify required Hibernate properties in my
examples. Most of the properties take their default values and it is not required to specify them in the property
file unless it is really required. T his file is kept in the root directory of your application's classpath.

Hibernate Properties:
Following is the list of important properties you would require to config ure for a databases in a standalone
situation:

S.N.

Properties and Desc ription

1

hibernate.dialec t
T his property makes Hibernate g enerate the appropriate SQL for the chosen database.

2

hibernate.c onnec tion.driver_c lass
T he JDBC driver class.

3

hibernate.c onnec tion.url
T he JDBC URL to the database instance.

4

hibernate.c onnec tion.username
T he database username.

5

hibernate.c onnec tion.password
T he database password.

6

hibernate.c onnec tion.pool_size
Limits the number of connections waiting in the Hibernate database connection pool.

7

hibernate.c onnec tion.autoc ommit
Allows autocommit mode to be used for the JDBC connection.

If you are using a database along with an application server and JNDI then you would have to config ure the
following properties:

S.N.

Properties and Desc ription

1

hibernate.c onnec tion.datasourc e
T he JNDI name defined in the application server context you re using for the application.

2

hibernate.jndi.c lass
T he InitialContext class for JNDI.

3

hibernate.jndi.
Passes any JNDI property you like to the JNDI InitialContext.

4

hibernate.jndi.url
Provides the URL for JNDI.

5

hibernate.c onnec tion.username
T he database username.

6

hibernate.c onnec tion.password
T he database password.

Hibernate with MySQL Database:
MySQL is one of the most popular open-source database systems available today. Let us create
hibernate.c fg .xml config uration file and place it in the root of your application's classpath. You would have to
make sure that you have testdb database available in your MySQL database and you have a user test available
to access the database.
T he XML config uration file must conform to the Hibernate 3 Config uration DT D, which is available from
http://www.hibernate.org /dtd/hibernate-config uration-3.0.dtd.





org.hibernate.dialect.MySQLDialect


com.mysql.jdbc.Driver



jdbc:mysql://localhost/test


root


root123







T he above config uration file includes  tag s which are related to hibernate-mapping file and we will
see in next chapter what exactly is a hibernate mapping file and how and why do we use it. Following is the list of
various important databases dialect property type:

Database

Dialec t Property

DB2

org .hibernate.dialect.DB2Dialect

HSQLDB

org .hibernate.dialect.HSQLDialect

HypersonicSQL

org .hibernate.dialect.HSQLDialect

Informix

org .hibernate.dialect.InformixDialect

Ing res

org .hibernate.dialect.Ing resDialect

Interbase

org .hibernate.dialect.InterbaseDialect

Microsoft SQL Server 2000

org .hibernate.dialect.SQLServerDialect

Microsoft SQL Server 2005

org .hibernate.dialect.SQLServer2005Dialect

Microsoft SQL Server 2008

org .hibernate.dialect.SQLServer2008Dialect

MySQL

org .hibernate.dialect.MySQLDialect

Oracle (any version)

org .hibernate.dialect.OracleDialect

Oracle 11g

org .hibernate.dialect.Oracle10g Dialect

Oracle 10g

org .hibernate.dialect.Oracle10g Dialect

Oracle 9i

org .hibernate.dialect.Oracle9iDialect

Postg reSQL

org .hibernate.dialect.Postg reSQLDialect

Prog ress

org .hibernate.dialect.Prog ressDialect

SAP DB

org .hibernate.dialect.SAPDBDialect

Sybase

org .hibernate.dialect.SybaseDialect

Sybase Anywhere

org .hibernate.dialect.SybaseAnywhereDialect

Hibernate Examples
Let us try an example of using Hibernate to provide Java persistence in a standalone application. We will g o
throug h different steps involved in creating Java Application using Hibernate technolog y.

Create POJO Classes:
The first step in creating an application is to build the Java POJO class or
classes, depending on the application that will be persisted to the
database. Let us consider our Employee class with g etXXX and setXXX
methods to make it JavaBeans compliant class.
A POJO (Plain Old Java Object) is a Java object that doesn't extend or
implement some specialized classes and interfaces respectively required

by the EJB framework. All normal Java objects are POJO.
When you desig n a classs to be persisted by Hibernate, it's important to
provide JavaBeans compliant code as well as one attribute which would
work as index like id attribute in the Employee class.
public class Employee {
private int id;
private String firstName;
private String lastName;
private int salary;
public Employee() {}
public Employee(String fname, String lname, int salary) {
this.firstName = fname;
this.lastName = lname;
this.salary = salary;
}
public int getId() {
return id;
}
public void setId( int id ) {
this.id = id;
}
public String getFirstName() {
return firstName;
}
public void setFirstName( String first_name ) {
this.firstName = first_name;
}
public String getLastName() {
return lastName;
}
public void setLastName( String last_name ) {
this.lastName = last_name;
}
public int getSalary() {
return salary;
}
public void setSalary( int salary ) {
this.salary = salary;
}
}

Create Database Tables:
Second step would be creating tables in your database. T here would be one table corresponding to each object
you are willing to provide persistence. Consider above objects need to be stored and retrieved into the
following RDBMS table:
create table EMPLOYEE (
id INT NOT NULL auto_increment,
first_name VARCHAR(20) default NULL,
last_name VARCHAR(20) default NULL,
salary
INT default NULL,
PRIMARY KEY (id)
);

Create Mapping Config uration File:
T his step is to create a mapping file that instructs Hibernate how to map the defined class or classes to the
database tables.






This class contains the employee detail.










You should save the mapping document in a file with the format .hbm.xml. We saved our mapping
document in the file Employee.hbm.xml. Let us see little detail about the mapping document:
T he mapping document is an XML document having  as the root element which
contains all the  elements.
T he  elements are used to define specific mapping s from a Java classes to the database tables.
T he Java class name is specified using the name attribute of the class element and the database table
name is specified using the table attribute.
T he  element is optional element and can be used to create the class description.
T he  element maps the unique ID attribute in class to the primary key of the database table. T he
name attribute of the id element refers to the property in the class and the c olumn attribute refers to the
column in the database table. T he type attribute holds the hibernate mapping type, this mapping types will
convert from Java to SQL data type.
T he  element within the id element is used to automatically g enerate the primary key
values. Set the c lass attribute of the g enerator element is set to native to let hibernate pick up either
identity, sequenc e or hilo alg orithm to create primary key depending upon the capabilities of the
underlying database.
T he  element is used to map a Java class property to a column in the database table. T he
name attribute of the element refers to the property in the class and the c olumn attribute refers to the
column in the database table. T he type attribute holds the hibernate mapping type, this mapping types will
convert from Java to SQL data type.
T here are other attributes and elements available which will be used in a mapping document and I would try to
cover as many as possible while discussing other Hibernate related topics.

Create Application Class:
Finally, we will create our application class with the main() method to run the application. We will use this
application to save few Employee's records and then we will apply CRUD operations on those records.
import java.util.List;
import java.util.Date;
import java.util.Iterator;
import
import
import
import
import

org.hibernate.HibernateException;
org.hibernate.Session;
org.hibernate.Transaction;
org.hibernate.SessionFactory;
org.hibernate.cfg.Configuration;

public class ManageEmployee {
private static SessionFactory factory;
public static void main(String[] args) {
try{
factory = new Configuration().configure().buildSessionFactory();
}catch (Throwable ex) {
System.err.println("Failed to create sessionFactory object." + ex);
throw new ExceptionInInitializerError(ex);
}

ManageEmployee ME = new ManageEmployee();
/* Add few employee records in database */
Integer empID1 = ME.addEmployee("Zara", "Ali", 1000);
Integer empID2 = ME.addEmployee("Daisy", "Das", 5000);
Integer empID3 = ME.addEmployee("John", "Paul", 10000);
/* List down all the employees */
ME.listEmployees();
/* Update employee's records */
ME.updateEmployee(empID1, 5000);
/* Delete an employee from the database */
ME.deleteEmployee(empID2);
/* List down new list of the employees */
ME.listEmployees();
}
/* Method to CREATE an employee in the database */
public Integer addEmployee(String fname, String lname, int salary){
Session session = factory.openSession();
Transaction tx = null;
Integer employeeID = null;
try{
tx = session.beginTransaction();
Employee employee = new Employee(fname, lname, salary);
employeeID = (Integer) session.save(employee);
tx.commit();
}catch (HibernateException e) {
if (tx!=null) tx.rollback();
e.printStackTrace();
}finally {
session.close();
}
return employeeID;
}
/* Method to READ all the employees */
public void listEmployees( ){
Session session = factory.openSession();
Transaction tx = null;
try{
tx = session.beginTransaction();
List employees = session.createQuery("FROM Employee").list();
for (Iterator iterator =
employees.iterator(); iterator.hasNext();){
Employee employee = (Employee) iterator.next();
System.out.print("First Name: " + employee.getFirstName());
System.out.print(" Last Name: " + employee.getLastName());
System.out.println(" Salary: " + employee.getSalary());
}
tx.commit();
}catch (HibernateException e) {
if (tx!=null) tx.rollback();
e.printStackTrace();
}finally {
session.close();
}
}
/* Method to UPDATE salary for an employee */
public void updateEmployee(Integer EmployeeID, int salary ){
Session session = factory.openSession();
Transaction tx = null;
try{
tx = session.beginTransaction();
Employee employee =
(Employee)session.get(Employee.class, EmployeeID);
employee.setSalary( salary );
session.update(employee);
tx.commit();
}catch (HibernateException e) {
if (tx!=null) tx.rollback();
e.printStackTrace();

}finally {
session.close();
}
}
/* Method to DELETE an employee from the records */
public void deleteEmployee(Integer EmployeeID){
Session session = factory.openSession();
Transaction tx = null;
try{
tx = session.beginTransaction();
Employee employee =
(Employee)session.get(Employee.class, EmployeeID);
session.delete(employee);
tx.commit();
}catch (HibernateException e) {
if (tx!=null) tx.rollback();
e.printStackTrace();
}finally {
session.close();
}
}
}

Compilation and Execution:
Here are the steps to compile and run the above mentioned application. Make sure you have set PAT H and
CLASSPAT H appropriately before proceeding for the compilation and execution.
Create hibernate.cfg .xml config uration file as explained in config uration chapter.
Create Employee.hbm.xml mapping file as shown above.
Create Employee.java source file as shown above and compile it.
Create Manag eEmployee.java source file as shown above and compile it.
Execute Manag eEmployee binary to run the prog ram.
You would g et following result, and records would be created in EMPLOYEE table.
$java ManageEmployee
.......VARIOUS LOG MESSAGES WILL DISPLAY HERE........
First
First
First
First
First

Name:
Name:
Name:
Name:
Name:

Zara
Daisy
John
Zara
John

Last Name: Ali Salary: 1000
Last Name: Das Salary: 5000
Last Name: Paul Salary: 10000
Last Name: Ali Salary: 5000
Last Name: Paul Salary: 10000

If you check your EMPLOYEE table, it should have following records:
mysql> select * from EMPLOYEE;
+----+------------+-----------+--------+
| id | first_name | last_name | salary |
+----+------------+-----------+--------+
| 29 | Zara
| Ali
|
5000 |
| 31 | John
| Paul
| 10000 |
+----+------------+-----------+--------+
2 rows in set (0.00 sec
mysql>



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