Basic Hibernate Annotations example

As part of my POC, today I developed a simple hibernate annotations based example. To run this example, you need JDK 5.0 or higher and hibernate 3.2.0.GA or above. I am using JDK 1.6, MySql 5.1, Tomcat 6.0.18 and Hibernate 3.3.1.GA.

Create hibernate.cfg.xml file. This file should be available in the classpath at runtime. I developed this example as part of a web application and I am using a datasource defined in my container. See my earlier post on How to configure a datasource in Tomcat

<?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="connection.datasource">java:comp/env/jdbc/travel</property>
  <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
  <property name="current_session_context_class">thread</property>
  <property name="show_sql">true</property>
  <mapping class="com.travel.domain.Airline"/>
 </session-factory>
</hibernate-configuration>

This example needs following table in your database.

CREATE TABLE airline (
   code char(2) PRIMARY KEY,
   name varchar(50) NOT NULL,
   created timestamp  DEFAULT NOW() NOT NULL
);

Create HibernateUtil class which provides Hibernate session to interact with database. new AnnotationConfiguration().configure() looks for hibernate.cfg.xml in the classpath, so make sure to deploy the file in WEB-INF/classes directory.

package com.travel.hibernate.util;

import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;

public class HibernateUtil {
    private static final SessionFactory sessionFactory;

    static {
        try {
            sessionFactory = new AnnotationConfiguration().configure()
                                                          .buildSessionFactory();
        } catch (Throwable ex) {
            System.err.println("Initial SessionFactory creation failed." + ex);
            throw new ExceptionInInitializerError(ex);
        }
    }

    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }
}

Airline class maps with the airline table we created above. Notice the annotations used to define the mapping.

package com.travel.domain;

import java.io.Serializable;
import java.util.Date;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name = "airline")
public class Airline implements Serializable {
    private static final long serialVersionUID = 6864693643526282786L;
    @Id
    @Column(name = "code")
    private String code;
    @Column(name = "name")
    private String name;
    @Column(name = "created")
    private Date createdTime;

    public String getCode() {
        return code;
    }

    public void setCode(String code) {
        this.code = code;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Date getCreatedTime() {
        return createdTime;
    }
}

Simple servlet to test the application. I used the hibernate code directly in my servlet for simplicity. You should define one DAO layer to encapsulate the hibernate code. To test acccess your servelt use url like http://host:port/travel/AirlineServlet?code=LH&name=Lufthansa

package com.travel.servlet;

import com.travel.domain.Airline;
import com.travel.hibernate.util.HibernateUtil;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class AirlineServlet extends HttpServlet {
    private static final long serialVersionUID = 2409603422056073641L;

    protected void service(HttpServletRequest request,
        HttpServletResponse response) throws ServletException, IOException {
        SessionFactory session = HibernateUtil.getSessionFactory();
        Session sess = session.getCurrentSession();
        Transaction tx = sess.beginTransaction();
        // Get the airline code and name
        String airlineCode = request.getParameter("code");
        String airlineName = request.getParameter("name");
        // Create Airline object
        Airline  airline = new Airline();
        airline.setCode(airlineCode);
        airline.setName(airlineName);
        // Save the record in database
        sess.save(airline);
        tx.commit();
        session.close();
    }
}