Sun Java System Message Queue 4.3 Developer's Guide for Java Clients

Connection Event Notification

Connection event notifications allow a Message Queue client to listen for closure and reconnection events and to take appropriate action based on the notification type and the connection state. For example, when a failover occurs and the client is reconnected to another broker, an application might want to clean up its transaction state and proceed with a new transaction.

If the Message Queue provider detects a serious problem with a connection, it calls the connection object's registered exception listener. It does this by calling the listener's onException method, and passing it a JMSException argument describing the problem. In the same way, the Message Queue provider offers an event notification API that allows the client runtime to inform the application about connection state changes. The notification API is defined by the following elements:

The com.sun.messaging.jms.notification package, which defines the event listener and the notification event objects .
The com.sun.messaging.jms.Connection interface, which defines extensions to the javax.jms.Connection interface.

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

Connection Events

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

Note that the JMS exception listener is not called when a connection event occurs. The exception listener is only called if the client runtime has exhausted its reconnection attempts. The client runtime always calls the event listener before the exception listener.

Table 3–5 Notification Events


Event Type	Meaning
`ConnectionClosingEvent`	The Message Queue client runtime generates this event when it receives a notification from the broker that a connection is about to be closed due to a shutdown requested by the administrator.
`ConnectionClosedEvent`	The Message Queue client runtime generates this event when a connection is closed due to a broker error or when it is closed due to a shutdown or restart requested by the administrator. When an event listener receives a `ConnectionClosedEvent,` the application can use the `getEventCode()` method of the received event to get an event code that specifies the cause for closure.
`ConnectionReconnectedEvent`	The Message Queue client runtime has reconnected to a broker. This could be the same broker to which the client was previously connected or a different broker. An application can use the `getBrokerAddress` method of the received event to get the address of the broker to which it has been reconnected.
`ConnectionReconnectFailedEvent`	The Message Queue client runtime has failed to reconnect to a broker. Each time a reconnect attempt fails, the runtime generates a new event and delivers it to the event listener. The JMS exception listener is not called when a connection event occurs. It is only called if the client runtime has exhausted its reconnection attempts. The client runtime always calls the event listener before the exception listener.

Creating an Event Listener

The following code example illustrates how you set a connection event listener. Whenever a connection 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();

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

com.sun.messaging.jms.notification.EventListener eListener = 
       new ApplicationEventListener();

//set event listener to the MQ connection.

connection.setEventListener ( eListener );

Event Listener Examples

In this example, an application chooses to have its event listener log the connection event to the application's logging system.

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

public void onEvent ( com.sun.messaging.jms.notification.Event connEvent ) {
      	log (connEvent);
}
private void log ( com.sun.messaging.jms.notification.Event connEvent ) {
	       String eventCode = connEvent.getEventCode(); 
      	String eventMessage = connEvent.getEventMessage();
    	  //write event information to the output stream.
     	}
}