Basic Hibernate Application in Eclipse

This tutorial demonstrates how to use Hibernate which is an Object relational mapping tool for Java platform.

This is a simple example of creating an object in Java and mapping it to a table in mysql database. (inserting rows into the mysql database using Hibernate)

Before we start with the application we need the following:

• Tomcat 5.0 or above. Click here to download
• Eclipse IDE ( Enterprise Edition).
• Hibernate x.x  jar files. For the latest version of jar files Click here to download
• MySQL database
• MySQL ODBC driver jar file. Click here to download

Step 1: Create a Java project in Eclipse.

Step 2: Provide a name for your project and click on ‘Finish’

Step 3: Add the following jars (which are present in the downloaded hibernate x.x -> lib -> required folder)  and also the downloaded mysql odbc jar file to the project by right clicking on the project name followed by Properties ->Java Build Path -> Libraries -> Add External jars

Step 4: Create the hibernate.cfg.xml file in the src folder of the project and copy the following code into the xml file:

	<?xml version='1.0' encoding='UTF-8'?>
	<!DOCTYPE hibernate-configuration PUBLIC
	"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
	<hibernate-configuration>
	<session-factory>
	<property name="dialect">org.hibernate.dialect.MySQLDialect</property>
	<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
	<property name="connection.url">jdbc:mysql://localhost:port/database_name</property>
	<property name="connection.username">root</property>
	<property name="connection.password">password</property>
	<property name="cache.provider_class">org.hibernate.cache.HashtableCacheProvider</property>
	<property name="transaction.factory_class">org.hibernate.transaction.JDBCTransactionFactory</property>
	<property name="current_session_context_class">thread</property>
	<property name="hibernate.show_sql">true</property>
	<property name="hibernate.hbm2ddl.auto">create</property>
	<mapping class="com.model.Employee"/>
	</session-factory>
	</hibernate-configuration>

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Step 5: Update the hibernate.cfg.xml file parameters ( port number, database name, username password). The final hibernate.cfg.xml should look as follows:

Step 6: Create a package ‘com.model’ and create two classes named ‘Employee’ and ‘HibernateMain’ within that package and paste the following codes in the respective class files:

Employee.java

	package com.model;
	import java.util.Date;
	import javax.persistence.Entity;
	import javax.persistence.Id;
	import javax.persistence.Table;
	@Entity
	@Table (name="employee")
	public class Employee {
	@Id
	private int eid;
	private String ename;
	private String eadd;
	private Date doj;
	public int getEid() {
	return eid;
	}
	public void setEid(int eid) {
	this.eid = eid;
	}
	public String getEname() {
	return ename;
	}
	public void setEname(String ename) {
	this.ename = ename;
	}
	public String getEadd() {
	return eadd;
	}
	public void setEadd(String eadd) {
	this.eadd = eadd;
	}
	public Date getDoj() {
	return doj;
	}
	public void setDoj(Date doj) {
	this.doj = doj;
	}
	}

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Hibernate.java

	package com.model;
	import java.util.Date;
	import org.hibernate.Session;
	import org.hibernate.SessionFactory;
	import org.hibernate.cfg.Configuration;
	public class HibernateMain {
	public static void main(String[] args) {
	Configuration configuration=new Configuration();
	SessionFactory sf=configuration.configure().buildSessionFactory();
	Employee e1=new Employee();
	e1.setEid(1);
	e1.setEname("Sachin");
	e1.setEadd("India");
	e1.setDoj(new Date());
	Employee e2=new Employee();
	e2.setEid(2);
	e2.setEname("Rooney");
	e2.setEadd("Manchester");
	e2.setDoj(new Date());
	Session ss=sf.openSession();
	ss.beginTransaction();
	//saving objects to session
	ss.save(e1);
	ss.save(e2);
	ss.getTransaction().commit();
	ss.close();
	}
	}

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Step 7 : Your final directory structure should look as follows:

Step 8: Run the HibernateMain.java as a Java Application.  The console should show your insert queries as follows:

If you open mysql and check the database, the two employee rows should be present.

Notes:

• The Annotations in the Employee.java file help Hibernate decide the structure of the table to be created in the database. For example, @Entity tells Hibernate to treat this object as a table in the database. @Id annotation just above the declaration of parameter eid in the Employee.java file tells Hibernate to treat eid as the primary key of the table. @Table (name="employee") decides the name of the table which will be created in the database. 
• For every new model class for which we need to create a table we need to give the @Entity annotation in the class file itself and add the mapping parameter in the hibernate.cfg.xml file as <mapping class="com.model.class_name"/>
• The <property name="hibernate.hbm2ddl.auto">create</property>
  which is set to create in our example automatically creates a schema destroying the previous data
  The list of possible values for this parameter are,

1. validate: validate the schema, makes no changes to the database.
2. update: update the schema.
3. create: creates the schema, destroying previous data.
4. create-drop: drop the schema at the end of the session.