generator in hibernate annotations

//In this example we will see about the generators using annotations
UserDetails.java

package com.hibernate.model;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.GenerationType;

import javax.persistence.Id;

import javax.persistence.Table;

@Entity

@Table(name = "userdet")

public class UserDetails {

@Id

//1. @GeneratedValue(strategy=GenerationType.AUTO)

// The above annotation prints the id value from 1,2........ if it is AUTO

// 2.@GeneratedValue(strategy=GenerationType.IDENTITY)

/*

* Oracle doesn't support Identity it will print exception as

* org.hibernate.MappingException: org.hibernate.dialect.OracleDialect does

* not support identity key generation

*/

/*3.@GeneratedValue(strategy=GenerationType.SEQUENCE)

The above annotations takes the value where we stopped previously and it

prints*/

/*@GeneratedValue(strategy=GenerationType.TABLE)

The id value starting from 32768,32769,.......*/

private Integer userId;

public Integer getUserId() {

return userId;

}

public void setUserId(Integer userId) {

this.userId = userId;

}

public String getUserName() {

return userName;

}

public void setUserName(String userName) {

this.userName = userName;

}

private String userName;

}

UserAccess.java

package com.hibernate;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.cfg.Configuration;

import com.hibernate.model.UserDetails;

public class UserAccess {

public static void main(String[] args) {

// TODO Auto-generated method stub

UserDetails user = new UserDetails();

user.setUserName("karthik reddy");

UserDetails user2 = new UserDetails();

user2.setUserName("karthik");

SessionFactory factory = new Configuration().configure()

.buildSessionFactory();

Session session = factory.openSession();

session.beginTransaction();

session.save(user);

session.save(user2);

session.getTransaction().commit();

session.close();

factory.close();

}

}

hibernate.cfg.xml

<?xml version='1.0' encoding='utf-8'?>

<!DOCTYPE hibernate-configuration PUBLIC

"-//Hibernate/Hibernate Configuration DTD 3.0//EN"

"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

<session-factory>

<!-- Database connection settings -->

<property name="connection.driver_class">oracle.jdbc.OracleDriver</property>

<property name="connection.url">jdbc:oracle:thin:@localhost:1521:XE</property>

<property name="connection.username">system</property>

<property name="connection.password">system</property>

<!-- JDBC connection pool (use the built-in) -->

<property name="connection.pool_size">1</property>

<!-- SQL dialect -->

<property name="dialect">org.hibernate.dialect.OracleDialect</property>

<!-- Echo all executed SQL to stdout -->

<property name="show_sql">true</property>

<!-- Drop and re-create the database schema on startup -->

<property name="hbm2ddl.auto">update</property>

<mapping class="com.hibernate.model.UserDetails" />

</session-factory>

</hibernate-configuration>

NOTE:
 @GeneratedValue(strategy=GenerationType.AUTO) is better  to use which supports all the databases