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();
}
}
