Example: Work object

The following is an example of a work object that dynamically subscribes to a topic

class SampleWork implements Work
{
  boolean released;
  Topic targetTopic;
  EventSource es;
  TopicConnectionFactory tcf;

  public SampleWork(TopicConnectionFactory tcf, EventSource es, Topic targetTopic)
  {
    released = false;
    this.targetTopic = targetTopic;
    this.es = es;
    this.tcf = tcf;
  }

  synchronized boolean getReleased()
  {
    return released;
  }

  public void run()
  {
    try
    {
      // setup our JMS stuff.
      TopicConnection tc = tcf.createConnection();
      TopicSession sess = tc.createSession(false, Session.AUTOACK);
      tc.start();

      MessageListener proxy = es.getEventTrigger(MessageListener.class, false);
      while(!getReleased())
      {
        // block for up to 5 seconds.
        Message msg = sess.receiveMessage(5000);
        if(msg != null)
        {
          // fire an event when we get a message
          proxy.onMessage(msg);
        }
      }
      tc.close();
    }
    catch (JMSException ex)
    {
      // handle the exception here 
      throw ex;
    }
    finally
    {
      if (tc != null)
      {
        try
        { 
          tc.close();
        }
        catch (JMSExceptin ex1) 
        {
          // handle exception
        }
      }
    }
  }

  // called when we want to stop the Work object.
  public synchronized void release()
  {
    released = true;
  }
}

As a result, any component that has access to the event source can add an event on demand, which allows components to subscribe to a topic in a more scalable way than by simply giving each client subscriber its own thread. The previous example is fully explored in the WebSphere Trader Sample. See the Samples Gallery for details.

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See Also

Accessing the Samples (Samples Gallery)

 

Related Tasks

Developing work objects to run code in parallel

 

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