6 Using JPA with Coherence

In this exercise, you learn how to use Java Persistence API (JPA) to perform object-relational mapping. This chapter contains the following sections:

This exercise assumes that you have a working version of the Oracle Database 10g Express Edition (also known as the OracleXE database) installed on your system. If you do not have the database, you can download it here:


6.1 Introduction

A major enhancement in EJB technology is the addition of JPA, which simplifies the entity persistence model and adds capabilities, such as persistence for Java SE, that were not in the EJB 2.1 technology.

JPA deals with the way relational data is mapped to Java objects ("persistent entities"), the way that these objects are stored in a relational database so that they can be accessed at a later time, and the continued existence of an entity's state even after the application that uses it ends. In addition to simplifying the entity persistence model, the JPA standardizes object-relational mapping.

To determine how data is stored within a Coherence cluster, a backing map is used. By default, Coherence uses a memory-based backing map. To persist data, there are several backing map implementations.

You use the JPA implementation within this lesson. This implementation provides Object Relational Mapping (ORM) from the Java world to the database world, allowing you to use the standard Coherence get or put, and have the Coherence calls translated into database calls using JPA and Oracle TopLink (based on the open source EclipseLink project).

6.2 Mapping Relational Data to Java Objects with JPA

In this exercise, use JDeveloper to perform the following:

  • Create a connection to the HR schema in the OracleXE database.

  • Automatically generate JPA objects for the EMPLOYEES table.

  • Modify cache-server.cmd to point to the sample JPA cache-config.xml.

To use the Java Persistence API (JPA) to demonstrate data mapping with Coherence:

  1. Unlock the HR account in your pre-installed OracleXE database.

    It is assumed that you have the OracleXE database installed on your machine and can access the HR schema. To unlock the HR account, perform the following steps:

    1. Navigate to Start > All Programs> Oracle Database 10g Express Edition > Run SQL Command Line.

    2. Enter connect system as sysdba, and then enter welcome1 when prompted for the password. (Note this exercise assumes that your user name is system and password is welcome1).

      Figure 6-1 Connecting to the Database

      Connecting to the Database
    3. Enter the command to unlock the account:

      alter user hr identified by hr account unlock;

      Figure 6-2 Unlocking the Database Account

      Unlocking the Database Account
  2. Create a new project in JDeveloper called JPA. See "Creating a New Project in an Existing Application" if you need detailed information.

    1. Set the default Java Options in Run/Debug/Profile of the Project Properties to the appropriate log level and to disable local storage.

      -Dtangosol.coherence.distributed.localstorage=false  -Dtangosol.coherence.log.level=3
    2. Ensure that the classpath points to the full path for the coherence.jar file:

  3. Create a new database connection to the HR schema.

    1. In the Application Resources section of the navigator, right-click Connections, select New Connection, and then Database Connection.

    2. Enter the details to connect to your HR schema and click OK.

      Connection Name: XE_HR

      Connection Type: Oracle (JDBC)

      Username: hr

      Password: hr

      —Click Test Connection.

      This should display "Success!"

      Click OK.

      Figure 6-3 Defining the Database Connection

      Defining the Database Connection
    3. Right-click the JPA project and select New. Under Business Tier, select EJB, and then select Entities from Tables. Click OK.

      Figure 6-4 Creating EJB Entity Beans

      Creating EJB Entity Beans
    4. In the Create Entities from Tables window, select EJB 3.0 --JPA Entities, and then click Next.

      Figure 6-5 Specifying the EJB Version

      Specifying the EJB Version
    5. Click New to create a persistence unit. (Each persistence unit defines a set of classes and their mapping characteristics when persisting them.) Enter the following details and click OK.

      Name: JPA

      JTA Datasource Name: <leave blank>

      Non-JTA Datasource Name: <leave blank>

      Database Platform: Oracle

      Platform: None

      Click OK. When the Create Entities from Tables screen returns, click Next.

      Figure 6-6 Defining the Persistence Unit

      Defining the Persistance Unit
    6. Select the Online Database Connection option and click Next.

      Figure 6-7 Creating Entity Beans from Table Data

      Creating Entity Beans from Table Data
    7. In the Database Connection Details window, click Next.

      Figure 6-8 Choosing the Database Connection

      Choosing the Database Connection
    8. Query for the EMPLOYEES table and select it as shown in Figure 6-9. Click Next.

      Figure 6-9 Choosing the Table Data for the Entity Bean

      Choosing the Table Data for the Entity Bean
    9. Accept the default General Options and click Next.

      Figure 6-10 Choosing General Options for the Entity

      Choosing General Options for the Entity
    10. Accept the default Entity Class Details and click Next.

      Figure 6-11 Specifying the Entity Details

      Specifying the Entity Details
    11. A Summary page appears. Click Finish to create the Entity bean. You should see messages similar to Figure 6-12 in the EJB Log window of the navigator.

      Figure 6-12 Generating EJB Entity Beans—the EJB Log Window

      Generating EJB Entity Beans
    12. Replace the contents of persistence.xml with the code in Example 6-1 and save the file. Ensure that the connection details match your database connection details.

      Example 6-1 persistance.xml File Contents

      <persistence xmlns:xsi="http://www.w3.org/2001/XMLSchemainstance" version="1.0" xmlns="http://java.sun.com/xml/ns/persistence">
      <persistence-unit name="JPA" transaction-type="RESOURCE_LOCAL">
              <property name="eclipselink.logging.level" value="INFO"/>
              <property name="eclipselink.jdbc.driver" value="oracle.jdbc.OracleDriver"/>
              <property name="eclipselink.jdbc.url" value="jdbc:oracle:thin:@localhost:1521:XE"/>
              <property name="eclipselink.jdbc.password" value="hr"/>
              <property name="eclipselink.jdbc.user" value="hr"/>
  4. Create a cache configuration file for JPA.

    Open a text editor and create a file named jpa-cache-config.xml. Use the code illustrated in Example 6-2. Save the file in the home\oracle\labs\ directory.

    Example 6-2 Cache Configuration for JPA

    <?xml version="1.0" encoding="windows-1252" ?>
          <!-- Set the name of the cache to be the entity name  -->
          <!-- Configure this cache to use the scheme defined below  -->
          Define the cache scheme
                This param is the entity name
                This param is the fully qualified entity class
                This param should match the value of the
                persistence unit name in persistence.xml
  5. Copy the cache-server.cmd file and modify the server properties.

    1. Open a terminal window. Navigate to the /oracle/product/coherence/bin directory and copy the cache-server.cmd file to jpa-cache-server.cmd.

      cp cache-server.cmd jpa-cache-server.cmd
    2. Edit jpa-cache-server.cmd. Declare the cache configuration file in Java_OPTS:

    3. Add the following CLASSPATH to the -cp argument: C:\home\oracle\labs\JPA\classes;

    4. You must also add the following JAR files to the CLASSPATH:

      Coherence JPA libraries: C:\oracle\product\coherence\lib\coherence-jpa.jar

      JDBC libraries: C:\oracle\product\wlserver_10.3\server\lib\ojdbc5.jar

      javax.persistence.* libraries: C:\oracle\product\modules\javax.persistence_1.0.0.0_1-0.jar

      EclipseLink libraries: C:\oracle\product\jdeveloper\modules\oracle.toplink_11.1.1\eclipselink.jar

      C:\oracle\product\coherence\lib\coherence-jpa.jar; C:\oracle\product\wlserver_10.3\server\lib\ojdbc5.jar; C:\oracle\product\jdeveloper\modules\oracle.toplink_11.1.1\eclipselink.jar;

      Example 6-3 illustrates a modified jpa-cache-server.cmd file:

      Example 6-3 Modified jpa-cache-server.cmd File

      @echo off
      @rem This will start a cache server
      @rem specify the Coherence installation directory
      set coherence_home=c:/oracle/product/coherence
      @rem specify the JVM heap size
      set memory=512m
      if not exist "%coherence_home%\lib\coherence.jar" goto instructions
      if "%java_home%"=="" (set java_exec=java) else (set java_exec=%java_home%\bin\java)
      set java_opts="-Xms%memory% -Xmx%memory% -Dtangosol.coherence.cacheconfig=\home\oracle\labs\jpa-cache-config.xml"
      "%java_exec%" -server -showversion "%java_opts%" -cp "%coherence_home%\lib\coherence.jar;C:\home\oracle\labs\JPA\classes;C:\oracle\product\coherence\lib\coherence-jpa.jar;C:\oracle\product\wlserver_10.3\server\lib\ojdbc5.jar;C:\oracle\product\jdeveloper\modules\oracle.toplink_11.1.1\eclipselink.jar;C:\oracle\product\modules\javax.persistence_1.0.0.0_1-0.jar" com.tangosol.net.DefaultCacheServer %1
      goto exit
      echo Usage:
      echo   ^<coherence_home^>\bin\cache-server.cmd
      goto exit
      @echo on
    5. Save the jpa-cache-server.cmd file and ensure that all other cache servers are stopped. Run jpa-cache-server.cmd.

  6. Modify the JPA Project Properties.

    1. Edit the JPA Project Properties and modify the Run/Debug/Profile configuration. Append the following line to the existing Java Options.

    2. Add additional CLASSPATH entries to the existing project properties.

      Navigate to Tools > Project Properties > Libraries and Classpath. Use the Add JAR/Directory and Add Library buttons to add the following JAR files and libraries into CLASSPATH (Note: the coherence.jar file should already be present):

      TopLink predefined JDeveloper library. This will provide the required EclipseLink JARs and APIs

      Oracle JDBC predefined JDeveloper library for database connectivity

      Oracle XML Parser v2 predefined JDeveloper library for interpreting XML

      —Java Persistence JAR file for the persistence API: C:\oracle\product\modules\javax.persistence_1.0.0.0_1-0.jar

      The Libraries and Classpath screen should look similar to Figure 6-13:

    Figure 6-13 Adding JARs and Libraries to the Classpath

    Adding JARs to the Classpath
  7. Create a new class in the JPA project to interact with the Employee object.

    1. Create a new class with a main method called RunEmployeeExample. See "Creating a Java Class" if you need detailed information.

    2. Create the code to perform the following:

      —Get an employee using EMPLOYEE_ID. EMPLOYEE_ID should be a long data type.

      —Display the salary.

      —Give them a 10% pay raise.

      —Get the value again to confirm the pay raise.

      Example 6-4 illustrates a possible solution.

      Example 6-4 Sample Employee Class File

      package com.oracle.coherence.handson;
      import com.tangosol.net.CacheFactory;
      import com.tangosol.net.NamedCache;
      public class RunEmployeeExample {
          public RunEmployeeExample() {
          public static void main(String[] args) {
              long empId = 190L;  // emp 190 - Timothy Gates
              NamedCache employees = CacheFactory.getCache("Employees");
              Employees emp = (Employees)employees.get(empId);   
              System.out.println("Employee " + emp.getFirstName() + " " + 
                              emp.getLastName() + ", salary = $" + emp.getSalary() );
              // give them a 10% pay rise
              emp.setSalary( emp.getSalary() * 1.1);
              employees.put(empId, emp);
              Employees emp2 = (Employees)employees.get(empId);
              System.out.println("New Employee details are " + emp2.getFirstName() + " " + emp2.getLastName() + ", salary = $" + emp2.getSalary() );
    3. Run RunEmployeeExample.

      Now that the Employees class has been annotated to persist to the database using JPA, and you have included the persistence.xml file to tell JPA where your database is, Coherence employs a CacheStore implementation that uses JPA to load and store objects to the database. When you use the get(Object key) method, the following happens:

      —Coherence looks for the entry with the key.

      —If the entry has not already been cached, or it is expired from the cache, Coherence asks the backing map, which uses JPA and EclipseLink to retrieve the data.

      —If the entry is in the cache, Coherence returns the entry directly to the application without going through EclipseLink. When you use put(Object Key,Object Value), Coherence uses JPA through EclipseLink to persist any changes to the database.

      The output should look similar to the text illustrated Figure 6-14.

      Figure 6-14 Results from the RunEmployeeExample Application

      Results from the RunEmployeeExample Application