You can absolutely do this in JMS, just use a local queue for storing the messages; send to remote queue when receiver is available.
Option 1 (Ideal, Safe)
1) First, create a JMS Server in WebLogic, LocalJMSServer.
2) Make sure to target this resource only to the local WebLogic instance only.
3) Create a queue, tempQueue, for LocalJMSServer.
4) Your application always sends messages to tempQueue. Since that queue is local, the messages just sit on the queue, and they are persisted too which is nice in case server crashes.
5) You'll need a separate JMSServer configuration in WebLogic to host the remoteQueue since that queue will be targeted to a remote WebLogic instance.
6) Your application periodically checks the remote receiver for availability:
if( receiverIsAvailable()){
...
}
...when the receiver is available, dequeue messages from tempQueue and send to remoteQueue...
Queue tempQueue = (Queue) ctx.lookup("tempQueue");
QueueSession queueLocalSession =
queueConn.createQueueSession(false,
Session.CLIENT_ACKNOWLEDGE);
QueueReceiver queueReceiver = queueLocalSession.createReceiver(tempQueue);
TextMessage localMessage = (TextMessage) queueReceiver.receive();
//send to remote queue
Queue remoteQueue = (Queue) ctx.lookup("remoteQueue");
QueueSender queueSender = queueRemoteSession.createSender(remoteQueue);
Message newMessage = queueRemoteSession.createTextMessage(
localMessage.getText());
queueSender.send( newMessage);
//now acknowledge the message since we safely sent to remoteQueue
localMessage.acknowledge();
I like this approach because it's fully transactional; if anything goes wrong, you don't lose messages provided you use PERSISTENT mode. Also, when pulling message from tempQueue, you must use a synchronous receiver (as above), you can't use onMessage() since it processes messages from the local queue immediately.
Option 2 (Simpler, Less Safe)
You can also use in-memory queue (not JMS ) for storing the message content locally:
ArrayBlockingQueue queue = new ArrayBlockingQueue<String>();
queue.add(messageContents1);
queue.add(messageContents2);
...
Your application checks for resource availability on the receiving side, if it's available, just dequeue and send the real JMS messages with no delay:
if( receiverIsAvailable()){
while(!queue.isEmpty()){
Message message = session.createTextMessage();
message.setText(queue.take());
queueSender.send(message);
}
}
The problem with this approach is that messages stored in queue reside in memory; if the sender crashes, you'll lose those message.
Hope it helps!
