[jboss-dev-forums] [Design of Messaging on JBoss (Messaging/JBoss)] - Notifications over JBM core connections

[jmesnil]

As part of the management task, I'm implementing receiving management notifications over JBM core connections.

The idea is that a Core client can subscribe to notifications by asking the server to send a message to a given destination  every time a notification is triggered on the server (e.g. a queue is full, a queue is added to the server)

- the client creates a "management message", a Core message with well-known properties:
  * the ObjectName it wants to observe
  * the destination where the notification messages must be sent (specified by the client, can be any kind of destination, more likely either a topic or a temp queue)
- it sends the message to the server

- the server handles the message
  * the PostOffice detects it is a management message and pass it to the management service
  * the management service creates a NotificationListener for the given ObjectName
  
- Later on, when a notification is received by the listener (e.g. a queue is full)
  * the listener creates a Core message and fills it with the notifications information (who, when, what, etc.)
  * this core message is then routed by the PostOffice according to the destination set by the client
  
- the client will receive the Core message and process the notification information

So, the big idea is that a Core message is created on the /server-side/ as the result of a notification (internal to the server) and not as the result of receiving a message from a client.
I'm not sure about the best way to create a Core message on the server.

The ManagementService code looks like:


  | // when handling a "management message"
  | final SimpleString replyTo = (SimpleString)message.getProperty(ManagementMessageImpl.HDR_JMX_REPLYTO);
  | boolean subscribe = (Boolean)message.getProperty(ManagementMessageImpl.HDR_JMX_SUBSCRIBE_TO_NOTIFICATIONS);
  | if (subscribe)
  | {
  |    broadcaster.addNotificationListener(new NotificationListener() {
  |       public void handleNotification(Notification notification, Object handback)
  |       {
  |          ServerMessage notificationMessage = new ServerMessageImpl(0);
  |          notificationMessage.setDestination(replyTo);
  |          // FIXME no hard-coded value
  |          notificationMessage.setBody(new ByteBufferWrapper(ByteBuffer.allocate(1024)));
  |          notificationMessage.putBooleanProperty(ManagementMessageImpl.HDR_JMX_NOTIFICATION, true);
  |          notificationMessage.putStringProperty(new SimpleString("notif"), new SimpleString(notification.getMessage()));
  |          try
  |          {
  |             postOffice.route(notificationMessage);
  |          }
  |          catch (Exception e)
  |          {
  |             log.warn("problem while routing a notification message", e);
  |             // TODO unregister the listener for the broadcaster
  |          }
  |       }               
  |    }, null, null);
  | }
  | ...
  | 

The code to create the notificationMessage is not correct.
I need to use a proper message ID but, on the server-side, it is the storage manager which owns the ID sequence.
I could inject the storageManager into the managementService to get access to its generateID() but it smells like a bad idea.
I could create a new POJO, a ID generator, injected in both the storageManager and the managementService.

What do you think?
Does this make sense?


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