Simple Implementation of JPA ( Java Persistence API )

Implementing Simple JPA Application

Technology Stack

1.    Eclipse Java EE IDE for Web Developers - Version: Kepler Service Release 2

2.    Oracle Database 11g -

3.    Persistence Provider - EclipseLink JPA

4.    Architecture – Web Application (MVC)

Jars / Dependencies

     Eclipselink:   eclipselink-2.1.0.v20100614-r7608

     Javax Persistence: javax.persistence-2.1.0

     Oracle JDBC Driver: ojdbc14_g-10.2.0.4

To get started, follow these steps:

Create a Dynamic Web Project or a JPA Project in Eclipse:

·         If JPA project then you can notice the META-INF folder holding the persistence.xml (only if you have correctly set your build path)  if not you can configure build path by adding above dependencies.

·         If Web project you can create persistence.xml in your META-INF folder under webcontent.

We will need following files to complete implementation of Selecting / Creating a record in a Payment table:

a)    POJO class – representing an entity (Payment in our case)

b)    Persistence.xml – holding our database details, persistence provider, class for mapping with any table for data persist (Record insert in table)

c)    Service / DAO class – To create EntityManager instance and using which we can query database. (In JPA a database connection is represented by the EntityManager interface. In order to access and work with an ObjectDB database we need an EntityManager instance)

Sample Entity class

A Payment entity POJO class :

@Entity: To declare the class as a ORM framework’s object class

@Id: To declare the primary key for the Payment table in a Payment Entity class

@Column: To map the attribute in the Entity class with the actual column of the table.

Sample ORM.xml or persistence.xml

<?xml version="1.0" encoding="UTF-8"?>

<persistence version="2.0"

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_2_0.xsd">

<persistence-unit name="JPATestPaymentCreation">

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

    <class>payments.Payment</class>

       <properties>

          <property name="javax.persistence.jdbc.driver"

                    value="oracle.jdbc.driver.OracleDriver" />

          <property name="javax.persistence.jdbc.url"

                    value="jdbc:oracle:thin:@AAAA03:1521:AAAA3t" />

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

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

        </properties>

       </persistence-unit>

</persistence>

 Sample Service Implementation java file

import javax.persistence.EntityManager;

import javax.persistence.EntityManagerFactory;

import javax.persistence.Persistence;

import javax.persistence.Query;

import java.util.*;

public class TestInsertEmployeeViaJPA {

 private static final String PERSISTENCE_UNIT_NAME = "JPATestEmployeeCreation";

 private static EntityManagerFactory factory;

/**

* @param args

*/

public static void main(String[] args) {

factory = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);

        EntityManager em = factory.createEntityManager();

          

        // Read the existing entries and write to console

          Query q = em.createQuery("SELECT emp FROM Employee emp");

           

         List<Employee> empList = q.getResultList();

         for (Employee user : empList) {

              System.out.println(user.getTraceId());

         }

         System.out.println("Size: " + empList.size());

          

          // Create new Employee Record

          em.getTransaction().begin();

          

          Employee testEmployee = new Employee();

          testEmployee.setTraceId(57615061110567l);

          testEmployee.setId(9000);

          testEmployee.setTransactionId(3l);

          testEmployee.setStatusId(1);

          testEmployee.setObligationId(1571);

          testEmployee.setSentToDal(1l);

          

          em.persist(testEmployee);

          em.getTransaction().commit();

          em.close();    

}

}