Hi Folks,
Java persistence framework is high on demand now days. If
you mention JPA in your resume, it will catch hold of the interviewer and can
influence in fetching you the job. (Ha ha I am not joking here! though some of
you might be thinking :)-)
Ok lets come back to our topic JPA i.e. Java Persistence
API.The Java Persistence API provides an object/relational mapping for managing
relational data in enterprise beans, web components, and application clients.
It can also be used in Java SE applications, outside of the Java EE
environment.
Now we will try to understand practically how this will
work.
1> Download and install latest eclipse IDE. In my case I
have used Eclipse Indigo.
2> Download the latest apache tomcat. I have tomcat7.0
3> Once you have downloaded the tomcat extract it and
keep it in a folder.
4> Now in eclipse IDE, select File > New > other
and pick Server from the list.
Click Next and select Tomcat
v6.0 Server for the server definition. You'll need to
select a run time.
Click on Add link and you will be prompted for the next
window to add server runtime configurations.
Click on Browse button to add the location of tomcat
directory where you have extracted the tomcat. Then click finish. Upon clicking
finish it will take back you to previous window. In that also you click on
Finish button.
Now you are done with server configurations. Now let’s start
building a dynamic web project to learn JPA.
5> Click on File->New->Dynamic Web Project
Name your project and click on Next button.
No need to do anything, just click Next button.
Check generate web.xml checkbox and click on Finish.
Now you are done with creating dynamic web application!
Congratulations! Now let’s add the required library files to the build path. Below
are the required jar files.
ü
mysql-connector-java-5.1.21-bin.jar
(Off course I am using MySQL as my DB!)
To add these libraries to the build path of your project (off
course you should download them before from the links provided and add them
into you WEB-INF/lib location.) just right click on your
project->Properties->Java Build Path.
Then click on add Add JARs button and then click on your
project->Web Content->WEB-INF->lib then select the jars and click OK
button.
Next go to Order and Export tab click on Select All button
and then click on OK button.
6> Now let’s create our first entity. Note that we have
used Java Annotations in this class.
Right click on the project->New->Class
Give the package name as com and class name as User and
click on Finish button.
Now the contents of the class User is as below.
package com;
import
java.io.Serializable;
import
javax.persistence.Column;
import
javax.persistence.Entity;
import
javax.persistence.GeneratedValue;
import
javax.persistence.GenerationType;
/**
@Author : Sanjeev Kulkarni
@Created on :
05-Oct-201212:25:13 PM
@Project :
a
@Package :
@File :
User.java
@Comments :
Revision History :
Sl No. | Revision Date |
Changed By | Reasons
------------------------------------------------------------------------------------
**/
@Entity(name="User")
public class User implements Serializable{
private static final long serialVersionUID =
975983410088693889L;
public User(){
}
@Column(name="id")
@GeneratedValue(strategy=GenerationType.AUTO)
private int id;
@Column(name="name")
private String name;
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;
}
}
Now lets create a JSP page to print list of users
from the database using openjpa.
Right click on
project->New->Other->Web->JSP File and then click on Next button.
Give the name of the file as NewFile.jsp and click Finish button.
Now copy and paste the content of NewFile.jsp as
below.
<%@ page language="java" contentType="text/html;
charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html
PUBLIC "-//W3C//DTD
HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<%@page import="javax.persistence.EntityManager"%>
<%@page import="javax.persistence.EntityManagerFactory"%>
<%@ page import="com.User" %>
<%@page import="javax.persistence.Persistence"%>
<%@page import= "javax.persistence.Query"%>
<html>
<head>
<meta http-equiv="Content-Type"
content="text/html; charset=ISO-8859-1">
<title>::</title>
</head>
<body>
<%
final EntityManagerFactory emf;
final EntityManager em;
final String PERSISTENCE_UNIT_NAME = "projectjpa";
try{
emf = Persistence.createEntityManagerFactory("projectjpa");
em = emf.createEntityManager();
em.getTransaction().begin();
User user = new User();
Query query = em.createQuery("select x from
User x ");
out.println("Query returned: " +
query.getResultList().size());
em.getTransaction().commit();
em.close();
emf.close();
}
catch(Exception e){
out.println(e);
e.printStackTrace();
}
%>
</body>
</html>
Modify the web.xml descriptor file. Mention NewFile.jsp as
a welcome file.
xml version="1.0"
encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
<display-name>LearningOpneJPA</display-name>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.htm</welcome-file>
<welcome-file>NewFile.jsp</welcome-file>
<welcome-file>default.html</welcome-file>
<welcome-file>default.htm</welcome-file>
<welcome-file>default.jsp</welcome-file>
</welcome-file-list>
</web-app>
Copy and paste the below content into the persistence.xml file.
xml version="1.0"
encoding="UTF-8"?>
<persistence version="1.0"
xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd">
<persistence-unit name="projectjpa">
<provider>org.apache.openjpa.persistence.PersistenceProviderImpl</provider>
<class>com.User</class>
<properties>
<property name="openjpa.ConnectionURL"
value="jdbc:mysql://localhost:3306/test"/>
<property name="openjpa.ConnectionDriverName"
value="com.mysql.jdbc.Driver"/>
<property name="openjpa.ConnectionUserName"
value="root"/>
<property name="openjpa.ConnectionPassword"
value="root"/>
<property name="openjpa.Log"
value="DefaultLevel=WARN, Tool=INFO"/>
<property name="openjpa.DynamicEnhancementAgent"
value="false"/>
<property name="openjpa.RuntimeUnenhancedClasses"
value="supported"/>
</properties>
</persistence-unit>
</persistence>
7> Now open MySQL command prompt and create a database
called test.
Mysql> create database test;
Mysql>use test;
Mysql>create table user (id int not null primary key,
name varchar(200));
Mysql> insert into user vales(1,’ABC’);
Mysql> insert into user vales(2,’XYZ’);
8> Now right click on the project->Run As->Run on
Server
9> You should be able to open the eclipse internal web browser
and should be showed the result as below:
Query returned: 2
