Hibernate introduction

Hibernate is an Object/Relational Mapping tools that provides services to map the data of object’s properties into columns of database-tables. It persist Java objects to database table automatically and vice versa. Java Programmer will able to map domain model of their project to data model into database design. It emphasis programmer to think for their programming only. It removes all SQL requirements to work with database while using any RDBMS into project.

Data stored into instance variables of an Object is retired by Hibernate toll and it Stores it to the specified column of database table. It uses some configurations that determine what to map and how to map. This configuration is stored into XML file along with class file that is going to be mapped. Classes are simple POJOs and no require any dependency on any other class. These classes are called Entity or Entity Bean classes also. In entity classes all members are kept private and each member is accessed through public getX() and setX() method of corresponding  member. For example if class has name member, then it is declared as a private (i.e. private String name; ) and it will have two methods public void getName() and public void setName(String name).

This approach reduces time to develop database driven application. This framework replaces JDBC for developers, but it uses it to process all data. If you are using Hibernate or hibernate like Persistent tool, you no need to know about SQL, Database System because all complexities have been overlapped by framework. Hibernate provides its own query language to perform some advance operations with data tables instead of SQL. Almost all operations can be done using Hibernate Query Language and you can update, retrieve and delete data of tables.

Hibernate have some interesting features that simplify your life by reducing effort to programming for database logics.

• Hibernate allows you to develop POJO(plain old java object) Based persistence classes following object oriented features inheritance, polymorphism, association, composition and the java collection frame work.

• Hibernate allows to program persistence classes without using any dependency on other classes or package. Persistence class is simple class that neither extends ant class not implements any interface. It not requires any other classes from other package. So this class can be compiling without any problem.

• Hibernate supports lazy initialization, many fetching strategies, and optimistic locking with automatic versioning and time stamping. Hibernate requires no special database tables or fields and generates much of the SQL at system initialization time instead of runtime. Hibernate consistently offers superior performance over straight JDBC coding.

• Hibernate was designed to work in an application server cluster and deliver a highly scalable architecture. Hibernate scales well in any environment: Use it to drive your in-house Intranet that serves hundreds of users or for mission-critical applications that serve hundreds of thousands.

• This framework comes with bundled jar files from which you can remove jar files those are not required to your application according to your needs as well as you can add them later. You no need to place all jar file library on classpath. Hibernate is highly customizable and extensible. 

• Including support for Hibernate Query Language (HQL), Java Persistence Query Language (JPAQL), Criteria queries, and "native SQL" queries; all of which can be scrolled and paginated to suit your exact performance needs.

Ref. : http://www.hibernate.org/about/why-hibernate.html

Download from : http://sourceforge.net/projects/hibernate/files/hibernate3/

Before start anything you have to configure HSQL Database. Click Here to configure

Example
Contact.java

package pack;
public class Contact{
    private int id;
    private String name;
    private int phone;
    private String email;
    public int getId(){return id;}
    public void setId(int id){this.id=id;}
    public String getName(){ return name;}
    public void setName(String name){this.name=name;}
    public int getPhone(){return phone;}
    public void setPhone(int phone){this.phone=phone;}
    public String getEmail(){return email;}
    public void setEmail(String email){this.email=email;}
    public String toString(){
        return "Contact[id="+id+", name="+name+", phone="+phone+", email="+email+"]";
    }
}


ContactDataOperation1.java


import org.hibernate.cfg.Configuration;
import org.hibernate.SessionFactory;
import org.hibernate.Session;
import org.hibernate.Transaction;
public class ContactDataOperation1{
    public static void main(String ar[]){
        Configuration c=new Configuration();
        c.setProperty("hibernate.dialect","org.hibernate.dialect.HSQLDialect");
        c.setProperty("hibernate.connection.driver_class","org.hsqldb.jdbcDriver");
        c.setProperty("hibernate.connection.url","jdbc:hsqldb:hsql://localhost/testdb");
        c.setProperty("hibernate.connection.username","sa");
        c.setProperty("hibernate.connection.password","");
        c.addClass(pack.Contact.class);
        SessionFactory factory=c.buildSessionFactory();
        Session session=factory.openSession();
        Transaction tx=session.beginTransaction();
        pack.Contact contact=new pack.Contact();
        contact.setId(3);
        contact.setName("abc");
        contact.setPhone(33333333);
        contact.setEmail("abc@gmail.com");
        session.save(contact);
        tx.commit();
        session.close();
    }
}


Contact.hbm.xml


 version="1.0"?>
 hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="pack.Contact" table="contact">
        <id name="id" type="int" column="id">
        id>
        <property name="name" column="fullname" type="string"/>
        <property name="phone" column="mobilenumber" type="int"/>
        <property name="email" column="emailid" type="string"/>
    class>
>

Compile and arrange directory hierarchy as following

HIBERNATE2

│   Contact.java

│   ContactDataOperation1.class

│   ContactDataOperation1.java

├───lib

│     antlr-2.7.6.jar

│     commons-collections-3.1.jar

│     dom4j-1.6.1.jar

│     hibernate3.jar

│     hsqldb.jar

│     javassist-3.9.0.GA.jar

│     jta-1.1.jar

│     slf4j-api-1.5.8.jar

│     slf4j-simple-1.6.0.jar

│

└───pack

      Contact.class

      Contact.hbm.xml

Now start database server and create tables named contact. Database to be used is HSQLDB and you can read more how to deal with HSQLDB.

Open command prompt and go to hibernate2 directory , and execute following commands.

To set all jar files into classpath;

set CLASSPATH=%CLASSPATH%;lib/antlr-2.7.6.jar;lib/commons-collections-3.1.jar;lib/dom4j-1.6.1.jar;lib/hibernate3.jar;lib/hsqldb.jar;lib/javassist-3.9.0.GA.jar;lib/jta-1.1.jar;lib/slf4j-api-1.5.8.jar;lib/slf4j-simple-1.6.0.jar

To set java into path

set path=%path%;D:\Program Files\Java\jdk1.6.0_13\bin

Compile

…hibernate2>javac *.java

Run

…hibernate2>java ContactDataOperation1

OUTPUT

In database manager, execute “select * from contact” SQL query and you will get something like