Consumer Event Notification

Consumer event notifications allow a Message Queue client to listen for the existence of consumers on a destination. Thus, for example, a producer client can start or stop producing messages to a given destination based on the existence of consumers on the destination.

The following sections describe the events that can trigger notification and explain how you can create an event listener.

Consumer Events

The following table lists and describes the events that can be returned by the event listener.

Table 3-6 Cnsumer Notification Events

Creating a Consumer Event Listener

The following code example illustrates how you set and remove a consumer event listener. Whenever a consumer event occurs, the event listener's onEvent method will be invoked by the client runtime.

//create an MQ connection factory.

com.sun.messaging.ConnectionFactory factory =
    new com.sun.messaging.ConnectionFactory();

//create an MQ connection.

com.sun.messaging.jms.Connection connection = 
    (com.sun.messaging.jms.Connection)factory.createConnection();

//create an MQ session

com.sun.messaging.jms.Session session = 
    (com.sun.messaging.jms.Session)connection.createSession(false,
    Session.AUTO_ACKNOWLEDGE);

//create a queue

com.sun.messaging.Queue queue =
    (com.sun.messaging.Queue)session.createQueue(strQueueName);

//construct an MQ event listener.  The listener implements 
//com.sun.messaging.jms.notification.EventListener interface.

com.sun.messaging.jms.notification.EventListener consEvtListener = 
    new MyConsumerEventListener();

//set consumer event listener.

connection.setConsumerEventListener
    ( (com.sun.messaging.Destination)queue, consEvtListener );

//perform activities

//remove consumer event listener.

connection.removeConsumerEventListener
    ( (com.sun.messaging.Destination)queue );

Consumer Event Listener Examples

In this example, an application chooses to have its event listener set a boolean flag to give ongoing consumer availability information.

public class MyEventListener implements
    com.sun.messaging.jms.notification.EventListener {

  boolean consumerReady = false;

  MyEventListener(){
    consumerReady = false;
  }

  public void onEvent(com.sun.messaging.jms.notification.Event evt) {

    if (evt.getEventCode().equals(
        com.sun.messaging.jms.notification.ConsumerEvent.CONSUMER_NOT_READY
        )) {
      synchronized(this){
        consumerReady=false;
      }
    } else if (evt.getEventCode().equals(
        com.sun.messaging.jms.notification.ConsumerEvent.CONSUMER_READY
        )) {
      synchronized(this){
        consumerReady=true;
      }
    }
  }
}