Implementation

This section describes how OTN developers used message-driven beans (MDBs) to implement an alert system in the FBS 10g. The FBS 10g also uses MDBs to manage trade notifications, but because the implementation is essentially the same, it is not covered here. The Design section describes how OTN developers decided where to use MDBs.

There's relatively little Java code to write. The key is to get the right information into the right configuration files. Here are the major implementation tasks:

• Writing the MDB implementation class
  

• Configuring ejb-jar.xml
  

• Configuring orion-ejb-jar.xml
  

• Creating OC4J queues

• Sending messages to the queues

Writing the MDB Implementation Class

The Java class for an MDB must implement the MessageDrivenBean and MessageListener interfaces. They key method is onMessage, which is invoked by the container. The following listing shows the implementation of oracle.otnsample.ibfbs.admin.ejb.AlertQueue.

  public void onMessage(javax.jms.Message message) {
    try {
      // Initialize context for lookup
      Context ctx = new InitialContext();
      // Lookup for the mailservice bean in the JNDI tree
      MailServiceHome mailServiceHome =
                                 (MailServiceHome) ctx.lookup("MailService");
      // Get an instance of  mailservice
      MailService mailService = mailServiceHome.create();
      TextMessage txtMessage  = (TextMessage) message;
      // Based on the Alert Mode, send alert mail to either Email id or
      // Mobile mail box
      if (txtMessage.getStringProperty("alertMode").equals("M")) {
        mailService.sendMail(txtMessage.getStringProperty("mobile"),
                             "alerts@fbs.com",
                             "Stock Price Alert",
                             getTextMsg(
                               txtMessage.getStringProperty("accountNumber"),
                               txtMessage.getStringProperty("name"),
                               txtMessage.getStringProperty("symbol"),
                               txtMessage.getStringProperty("minlimit"),
                               txtMessage.getStringProperty("maxlimit"),
                               txtMessage.getFloatProperty("rate")));
      } else {
        mailService.sendMail(txtMessage.getStringProperty("email"),
                             "alerts@fbs.com",
                             "Stock Price Alert",
                             getHTMLMsg(
                               txtMessage.getStringProperty("accountNumber"),
                               txtMessage.getStringProperty("name"),
                               txtMessage.getStringProperty("symbol"),
                               txtMessage.getStringProperty("minlimit"),
                               txtMessage.getStringProperty("maxlimit"),
                               txtMessage.getFloatProperty("rate")));
      }
    } catch (Throwable ex) {  // Trap errors
      ex.printStackTrace();
    }
  }

Configuring ejb-jar.xml

The following listings come from the configuration file <fbs_home>\ejb\src\META-INF\ejb-jar.xml. The first listing below names the MDB, identifies the class that implements it, and specifies a destination class for associated messages.

   <message-driven>
    <ejb-name>AlertMessageBean</ejb-name>
    <ejb-class>oracle.otnsamples.ibfbs.admin.ejb.AlertQueue</ejb-class>
    <transaction-type>Container</transaction-type>
    <message-driven-destination>
      <destination-type>javax.jms.Queue</destination-type>
    </message-driven-destination>
  </message-driven>

The following listing defines the ExchangeQueue message-driven bean.

 <message-driven> 
   <ejb-name>ExchangeMessageBean</ejb-name>
   <ejb-class>oracle.otnsamples.ibfbs.admin.ejb.ExchangeQueue</ejb-class>
   <transaction-type>Container</transaction-type>
   <message-driven-destination>
     <destination-type>javax.jms.Queue</destination-type>

   </message-driven-destination>
</message-driven>

Configuring orion-ejb-jar.xml

The EJB 2.1 specification does not address the mapping of an MDB to a destination (queue), so OTN developers used orion-ejb-jar.xml to do the mapping.The following listing from <fbs_home>\ejb\src\META-INF\orion-ejb-jar.xml specifies MDB deployment information.

    <message-driven-deployment name="AlertMessageBean" 
      destination-location="jms/AlertQueue" 
      connection-factory-location="jms/AlertQueueConnectionFactory" />

Creating OC4J Queues

Edit <OC4J_HOME>/j2ee/home/config/jms.xml and add the following tags within the <jms-server> tag.

     <queue name="Exchange Queue" location="jms/ExchangeQueue">
       <description>FBS Exchage Queue</description>
     </queue>
   
     <queue name="Alert Queue" location="jms/AlertQueue">
       <description>FBS Alert queue</description>
     </queue>
   
     <queue-connection-factory name="jms/ExchangeQueueConnectionFactory"
        location="jms/ExchangeQueueConnectionFactory"/>
   
     <queue-connection-factory name="jms/AlertQueueConnectionFactory"
        location="jms/AlertQueueConnectionFactory"/>

Sending Messages to the Queues

In the FBS 10g, Exchange Trading Operations (Buy Stocks, Sell Stocks) as well as Alert processing are carried out using MDBs. This document has described the implementation of AlertsBean. You can also view the source file ExchangeQueue.java to see how FBS 10g uses MDBs to handle real-time asynchronous tasks such as trading operations.

You may also find the following snippet from TradeManagementSessionFacadeBean.java interesting.

// Lazy loading of QueueConn factory and Q conn
   if(exchageQConnfactory == null || exchangeQueue == null) {
   InitialContext ic = new InitialContext();
   exchageQConnfactory = (QueueConnectionFactory)ic.lookup(
   (String)connHash.get("EXCHQCONNFACTORY"));

   exchangeQueue = (Queue)ic.lookup((String)connHash.get("EXCHQUEUE"));
   }
   // Create Queue Connection
   qconn = exchageQConnfactory.createQueueConnection();

 qconn.start();

 session = qconn.createQueueSession(false, 1);

 // Create a message and set the trade details
   Message message = session.createMessage();
   message.setStringProperty("toAddress", userEmail);
   message.setStringProperty("symbol", symbol);
   message.setStringProperty("tradeDate", tradeDt);
   message.setStringProperty("tradeType", tradeType);
   message.setStringProperty("qty", quantity.toString());
   message.setJMSExpiration(18000L);

 // Send the message

   session.createSender(exchangeQueue).send(message);