Observers and notification

The Messaging Architecture declares a pair of mixin interfaces, which define session observers and entry observers.

A class that is defined as a session observer is notified of events such as shutdown warnings, new message arrival, and registration of new MTMs. A significant class belonging to a message client application, such as the application UI class, implements the interface to handle such events by updating the display or taking other appropriate action. The client’s Message Server session object can call back the interface whenever it completes a request to the Message Server.

Session observers are important in supporting run-time extensibility of the Messaging Architecture, as message client applications can be informed of new MTMs being registered. As the registry classes are session observers, they also can update their lists of the available MTM components, allowing new components to be loaded.

Entry observers are notified when an individual entry changes, or when access to a message store has been successfully gained.