Callback interface for receiving messages on the bus. To receive messages on the message bus, create an implementation of this interface, then either annotate it with {@link Service @Service} or register it with the bus via acall to {@link MessageBus#subscribe(String,MessageCallback)} or{@link MessageBus#subscribeLocal(String,MessageCallback)}.
The subject of messages that a particular MessageCallback is interested in is specified when it is registered with the bus, however it is common practice for a MessageCallback class to have the same name as the bus subject it receives messages for. The {@link Service @Service} annotation makes thisapproach quite natural.
@see Service
@see MessageBus