Oracle TopLink with Message Driven Beans

Software Requirements

• Oracle TopLink 10g Release 3 (10.1.3), available from OTN.

• Oracle Containers for J2EE 10g Release 3 (10.1.3), available from OTN, or another application server (such as BEA WebLogic 6.1, 7.0, 8.1 or IBM WebSphere 4.0, 5.0)

Conventions

The following conventions are used in this document:

• <ORACLE_HOME> – the directory in which you installed Oracle TopLink.

Introduction

This How-To demonstrates a Message-Driven Bean using OracleAS TopLink to persist regular Java objects, with examples of

• Sessions

• Logging Messages

• Receiving Messages

This How To illustrates storing messages received from JMS (Java Message Service) into a database, then reading these stored messages. A simple JSP front-end with servlets to log and read messages from the database provide interaction.

Sessions

You must create the required server and client sessions for TopLink. For example, Example: Database Session shows a typical database session with the applicable getServerSession(), getSession(), getUnitOfWork(), and getNonTxUnitOfWork() methods.

public class SessionHelperSingleton {
  private static String SESSION_NAME = "messagedrivenbean"; // project name as it exists in the MW project file
  private static SessionHelperSingleton m_instance = null; // single instance of this class
 
  static {
  ConversionManager.getDefaultManager().setShouldUseClassLoaderFromCurrentThread(true);
  }
 
  // The default constructor for the class.
  private SessionHelperSingleton() {}
 
  // Return the (only) instance of this class.
  static SessionHelperSingleton getInstance() {
    if (m_instance == null) {
      m_instance = new SessionHelperSingleton();
    }
    return m_instance;
  }
 
  // Return a single session that supports multiple user/clients connection at the same time.
  private static Server getServerSession() {
    return (Server)SessionManager.getManager().getSession(SESSION_NAME, SessionHelperSingleton.class.getClassLoader());
  }
 
// Return a client session for this server session.
  static Session getSession() {
    return getServerSession().acquireClientSession();
  }
 
// Return the active unit of work for the current active external (JTS) transaction.
  static UnitOfWork getUnitOfWork() {
    return getServerSession().getActiveUnitOfWork();
  }

// Return a external transaction independant unit of work for this session.
  static UnitOfWork getNonTxUnitOfWork() {
    return getSession().acquireUnitOfWork();
  }}

Example: sesssions.xml shows a sample sessions.xml file for use with the previous database session.

<toplink-configuration>
   <session>
      <name>messagedrivenbean</name>
      <project-xml>MessageDrivenProject.xml</project-xml>
      <session-type>
         <server-session/>
      </session-type>
      <login>
         <type>oracle.toplink.sessions.DatabaseLogin</type>
         <datasource>java:comp/env/jdbc/JTSTopLinkDS</datasource>
         <platform-class>oracle.toplink.internal.databaseaccess.OraclePlatform</platform-class>
         <uses-external-connection-pool>true</uses-external-connection-pool>
         <uses-external-transaction-controller>true</uses-external-transaction-controller>
         <non-jts-datasource>java:comp/env/jdbc/JTSTopLinkDS</non-jts-datasource>
      </login>
      <external-transaction-controller-class>oracle.toplink.jts.oracle9i.Oracle9iJTSExternalTransactionController</external-transaction-controller-class>
      <enable-logging>true</enable-logging>
      <logging-options/>
   </session>
</toplink-configuration>

Logging Messages

To log a message to the database, TopLink executes the following in a unit of work:

UPDATE SEQUENCE SET SEQ_COUNT = SEQ_COUNT + 50 WHERE SEQ_NAME = 'Msg_SEQ'
SELECT SEQ_COUNT FROM SEQUENCE WHERE SEQ_NAME = 'Msg_SEQ'
INSERT INTO MESSAGES (M_MESSAGE, M_DATE, M_ID, M_SUBJECT) VALUES ('<message>', {d '<date>'}, <SEQUENCE NUMBER>, '<subject>')

In this example, TopLink provides a unique sequence number counter. TopLink executes the unit of work based on the following Java code:

public class LogMessageServlet extends HttpServlet {
  public void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
      request.setCharacterEncoding("UTF-8");
      response.setContentType("text/html; charset=UTF-8");
      getServletContext().log("LogMessages servlet - doGet");

      // redirect to post method
      doPost(request, response);
    }

    // Handle 'Post' request.
    public void doPost(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
        request.setCharacterEncoding("UTF-8");
        response.setContentType("text/html; charset=UTF-8");

        try {
          TopicConnectionFactory connectionFactory = (TopicConnectionFactory) new InitialContext().lookup("java:comp/env/jms/theTopicConnectionFactory");
          TopicConnection connection = connectionFactory.createTopicConnection();connection.start();
          TopicSession topicSession = connection.createTopicSession(false, Session.AUTO_ACKNOWLEDGE);
          Topic topic = (Topic) new InitialContext().lookup("java:comp/env/jms/theTopic");
          TopicPublisher publisher = topicSession.createPublisher(topic);
          // create a message using user input
          Message message = topicSession.createMessage();
          message.setJMSType("messageLogger");
          message.setLongProperty("time", System.currentTimeMillis());
          message.setStringProperty("subject", request.getParameter("subject"));
          message.setStringProperty("message", request.getParameter("message"));
          // publish the message
          publisher.publish(message);
          publisher.close();
          topicSession.close();
          connection.close();
        }
        catch (NamingException ne) {
          request.setAttribute("source", "LogMessageServlet doPost");
          request.setAttribute("header", "An Error Occurred");
          request.setAttribute("errorMessage", ne.getMessage());
          request.getRequestDispatcher("./errorPage.jsp").forward(request, response);
          return;
        }
       catch (JMSException jmse) {
          request.setAttribute("source", "LogMessageServlet doPost");
          request.setAttribute("header", "An Error Occurred");
          request.setAttribute("errorMessage", jmse.getMessage());
          request.getRequestDispatcher("./errorPage.jsp").forward(request, response);
          return;
       }
  }
}

Each time a message is published (illustrated in the LogMessageServlet code snippet) the onMessage() method is called and the message is then logged to the database using the following code:

/**
* Called upon receipt of message associated with the queue/topic this bean is * registered with.
*  * @see javax.jms.MessageListener#onMessage(Message)
*/
public void onMessage(Message message) {
  try {
  // print the received message
  System.out.println("Received message: '" + message.getStringProperty("message") + "'"); 
  // since there is no associated external transaction, get a non-transactional unit of work
  UnitOfWork uow = SessionHelperSingleton.getInstance().getNonTxUnitOfWork();
  Messages msgObject = (Messages) uow.registerObject(new Messages());

  msgObject.setSubject(message.getStringProperty("subject"));
  msgObject.setMessage(message.getStringProperty("message"));
  msgObject.setM_date(new Date(message.getLongProperty("time")));
  uow.commit();
  } catch (JMSException jmse) {
    System.out.println("JMS Exception: " + jmse.getMessage());
  }
}

Receiving Messages

To receive a specific message from the database, TopLink executes the following in a unit of work:

SELECT M_ID, M_MESSAGE, M_DATE, M_SUBJECT FROM MESSAGES

TopLink executes the unit of work based on the following Java code:

public Messages getMessage(String id) {
  Messages msg;
  try {
    ExpressionBuilder builder = new ExpressionBuilder();
    Expression exp = builder.get("m_id").equal(id);
    Session session = SessionHelperSingleton.getInstance().getSession();
    msg = (Messages) (session.readObject(Messages.class, exp));
  }
  catch (Exception e) {
    System.out.println("Exception: " + e.getMessage());
    return null;
  }
  return msg;
}

Summary

This How-To has shown examples of using TopLink with message driven beans.