Create a Message Listener for Asynchronous Message Consumption

EMS allows a Message Consumer to consume messages either synchronously or asynchronously. For synchronous consumption, the Message Consumer explicitly calls a receive method on the topic or queue. For asynchronous consumption, you can implement a Message Listener that serves as an asynchronous event handler for messages.

A Message Listener implementation has one method, onMessage, that is called by the EMS server when a message arrives on a destination. You implement the onMessage method to perform the desired actions when a message arrives. Your implementation should handle all exceptions, and it should not throw any exceptions.

Once you create a Message Listener, you must register it with a specific Message Consumer before calling the connection’s start method to begin receiving messages.

A Message Listener is not specific to the type of the destination. The same listener can obtain messages from a queue or a topic, depending upon the destination set for the Message Consumer with which the listener is registered.

• Java

  Create an implementation of the MessageListener interface, create a MessageConsumer, and use the MessageConsumer object’s setMessageListener() method to register the Message Listener with the Message Consumer:

     public class tibjmsAsyncMsgConsumer implements MessageListener
     {
        /* Create a connection, session and consumer */ 
     ...
        MessageConsumer QueueReceiver =
                                session.createConsumer(queue);
        QueueReceiver.setMessageListener(this);
        connection.start();
     }

  Note: Do not use the Session.setMessageListener() method, which is used by application servers, rather than by applications.

  Implement the onMessage() method to perform the desired actions when a message arrives:

     public void onMessage(Message message)
     {
          /* Process message and handle exceptions */
     }

  See the tibjmsAsyncMsgConsumer.java sample client for a working example.

• C

  Implement an onMessage() function to perform the desired actions when a message arrives:

     void onMessage(tibemsMsgConsumer QueueReceiver,
               tibemsMsg message, void* closure)
     {
          /* Process message and handle exceptions */
     }

  In another function, that creates a tibemsMsgConsumer and uses the tibemsMsgConsumer_SetMsgListener function to create a message listener for the Message Consumer, specifying onMessage() as the callback function:

  void run()
  {   
     tibemsMsgConsumer QueueReceiver = NULL;
     /* Create a connection, session and consumer */
     ...
     status = tibemsSession_CreateConsumer(session,
                   &QueueReceiver, queue, NULL, TIBEMS_FALSE);
     status = tibemsMsgConsumer_SetMsgListener(QueueReceiver,
                   onMessage, NULL);
     status = tibemsConnection_Start(connection);
  }

  See the tibemsAsyncMsgConsumer.c sample client for a working example.

• C#

  Create an implementation of the IMessageListener interface, use Session.CreateConsumer to create a MessageConsumer, and set the MessageListener property on the MessageConsumer object to register the Message Listener with the Message Consumer:

     public class csAsyncMsgConsumer : IMessageListener
     {
        /* Create a connection, session and consumer */
     ...      
        MessageConsumer QueueReceiver =
                   session.CreateConsumer(queue);
        QueueReceiver.MessageListener = this;
        connection.Start();
     }

  Implement the IMessageListener.OnMessage method to perform the desired actions when a message arrives:

      public void OnMessage(Message message) {
          try
          {
              /* Process message and handle exceptions */
          }
      }

  See the csAsyncMsgConsumer.cs and csAsyncMsgConsumerUsingDelegate.cs sample clients for working examples.

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