O'Reilly - Java Message Service

...
}
{
try {
Thread.sleep(10000);
} catch (java.lang.InterruptedException ie) { }
continue;
}
}
System.out.println("\nConnection established");
Java Message Service
The establishConnection( ) method then registers the ExceptionListener with the
connection via the setExceptionListener( ) method:
connect.setExceptionListener( (javax.jms.ExceptionListener) this);
Last, but not least, is the implementation of the onException( ) listener method. Its task is
to call the establishConnection( ) method again to re-establish a connection with the
JMS provider:
public void onException ( javax.jms.JMSException jmse)
{
// Tell the user that there is a problem
System.err.println ("\n\nThere is a problem with the connection.");
System.err.println (" JMSException: " + jmse.getMessage( ));
}
System.err.println ("Please wait while the application tries to "+
"reestablish the connection...");
connect = null;
establishConnection(mBroker, mUsername, mPassword);
When a connection is dropped and reestablished, all of the sessions, queues, publishers,
and subscribers need to be reestablished in order for the application to continue normal
processing. This is why we isolated all the connection logic in the establishConnection( )
method, so that it can be used during startup and reused if the connection is lost.
JMS does not define any reason codes for a dropped connection. However, a JMS provider
may provide a finer level of granularity by defining reason codes. Depending on the host
operating system's network settings, it may take a while for the provider to notice that a
connection has been dropped. Some providers implement a ping capability as a
configurable setting to detect a network loss.
6.6 Dead Message Queues
JMS provides mechanisms for guaranteed delivery of messages between clients, utilizing
the mechanisms we have discussed in this chapter. However, there are cases where
guaranteed delivery, acknowledgments, and transactional semantics are just not enough.
Many conditions may cause a message to be undeliverable. Messages may expire before
they reach their intended destination, or messages are viewed by the provider as
undeliverable due to some other reason such as a deployment configuration problem. A
message need not have an expiration associated with it, which means it would never
expire. Forever is a long time. Realistically, it would be more prudent if the JMS provider
could notify an application if a message cannot be delivered within a reasonable amount of
time.
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