Overview

Recently I just started playing with JPA (I used Hibernate and JDBC before). After reading some examples, I built a very simple program with JPA 2.0 (EclipseLink 2.1), Eclipse 3.5 Galileo and MySQL Server 5.1. I would like to summarize steps to build the program here.

Reference

1. EclipseLink 2.1.0 download page
2. Connector/J – MySQL JDBC driver
3. A Java Persistence Example
4. HelloWorld with JPA, TopLink and MySql

Steps

Download EclipseLink 2.1 and JDBC driver for MySQL Server 5.1

Use the above reference links to download EclipseLink 2.1 and MySQL 5.1 JDBC Driver. The JAR files we needed are eclipselink.jar, javax.persistence_2.0.1.v201006031150.jar and mysql-connector-java-5.1.13-bin.jar

Create Table

Use this SQL to create table bookbank for the example

DROP TABLE IF EXISTS `bookbank`;

CREATE TABLE `bookbank` (

  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,

  `title` varchar(45) NOT NULL DEFAULT '',

  `author` varchar(45) NOT NULL DEFAULT '',

  `price` double DEFAULT NULL,

  PRIMARY KEY (`id`)

)

Create a Connection Profile in Eclipse

A Connection Profile let you define a DB Connection and view Table Schema and Data in it. and the best part is it can generated Entity Bean for you according to connected DB Schemas!

1. Start "Eclipse", choose "File" –> "New" –> "Other…". Select "Connection Profile" in the wizard
   
2. At New Connection Profile, select MySQL for Connection Profile Type. Enter the name of the connection profile. Click Next
   
3. At next page. You have to choose a driver definition. If you don’t already have a MySQL 5.1 driver definition, you have to create it here. Click the "New Driver Definition" button (red rectangle) to do that.
   You can jump to step 6 if you already have a MySQL 5.1 driver definition.
   
4. At New Driver Definition, select the driver template with System Version 5.1. Enter MySQL 5.1 as the driver name. Click "Jar List" tab
   
5. At "Jar List" tab, remove any existing jar listed here. Than click "Add JAR/Zip…" and choose the mysql-connector-java-5.1.13-bin.jar file you just downloaded.
   Then click "OK" to create the definition
   
6. Back to the "New Connection Profile" window, choose the MySQL 5.1 driver definition you just created. Enter the Database, URL, Username and password for the connection. Remember to check "Save password" for future connection. Click "Finish" to create the profiile.
   

Create JPA Project in Eclipse

Next we have to create a JPA project in Eclipse.

1. Start "Eclipse", choose "File" –> "New" –> "Project…". Select "JPA Project" in the wizard
   
2. At "New JPA Project", enter project name. Select <None> for "Target runtime". Click "Next" twice
   
3. At this page, use the values listed below:
   - "Platform": Generic
   - "JPA Implementation": Disable Library Configuration (we will add the EclipseLink library manually)
   - "Connection": Choose the connection profile you have just created
   Note: If you select "Add driver library to build path", the driver library used in your connection profile will be added to the project. Otherwise you need to manually add the correct driver library.
   
4. Click "Finish" to create the project

Create Entity Bean from DB Table

1. In the JPA projec, add reference to eclipselink.jar, javax.persistence_2.0.1.v201006031150.jar libraries
2. Right click on the JPA project, select "New" –> "Entities From Tables"
   
3. The connection profile should be automatically selected, choose the bookbank table. Click "Next" three times
   
4. At this page, choose "identity" for "Key generator". Click "Finish"
   

Modify persistence.xml File

1. Open the "persistence.xml" file inside folder "META-INF", replace the "persistence-unit" tag with the following content:
   

   <persistence-unit name="JpaTest" transaction-type="RESOURCE_LOCAL">

       <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>

       <class>Bookbank</class>

       <properties>

           <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />

           <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/jpa_test" />

           <property name="javax.persistence.jdbc.user" value="MySQL_user_id" />

           <property name="javax.persistence.jdbc.password" value="MySQL_password" /> 

       </properties>

   </persistence-unit>

Create the testing console app

Now it’s time to test our JPA app! Let’s add a Java Class with the following code to the JPA project.

public class TestMain {

    public static void main(String[] args) {

        EntityManager em = Persistence

            .createEntityManagerFactory("JpaTest")

            .createEntityManager();

        EntityTransaction t = em.getTransaction();

        t.begin();

        Bookbank book = new Bookbank();

        book.setTitle("test title");

        book.setAuthor("test author");

        book.setPrice(123.456);

        em.persist(book);

        t.commit();

        t.begin();

        Bookbank resultBook = (Bookbank)em

            .createQuery("select b from Bookbank b order by b.id desc")

            .setMaxResults(1)

            .getSingleResult();

        System.out.println("Query result:");

        System.out.println("Id: " + resultBook.getId() 

                + ", title: " + resultBook.getTitle() 

                + ", author: " + resultBook.getAuthor() 

                + ", price: " + resultBook.getPrice());

        t.commit();

        em.close();

        System.exit(0);

    }

}

What the class do is simply insert a record with hardcoded values into bookbank table, and then select the newest record. We can start the "TestMain" class in Eclipse by right-clicking the class, "Run As" –> "Java Application"