Interface implemented by an MBean that emits Notifications. It
allows a listener to be registered with the MBean as a notification
listener.
Notification dispatch
When an MBean emits a notification, it considers each listener that has been
added with {@link #addNotificationListener addNotificationListener} and not
subsequently removed with {@link #removeNotificationListener removeNotificationListener}.
If a filter was provided with that listener, and if the filter's
{@link NotificationFilter#isNotificationEnabled isNotificationEnabled} method returns
false, the listener is ignored. Otherwise, the listener's
{@link NotificationListener#handleNotification handleNotification} method is called with
the notification, as well as the handback object that was provided to
{@code addNotificationListener}.
If the same listener is added more than once, it is considered as many times as it was
added. It is often useful to add the same listener with different filters or handback
objects.
Implementations of this interface can differ regarding the thread in which the methods
of filters and listeners are called.
If the method call of a filter or listener throws an {@link Exception}, then that
exception should not prevent other listeners from being invoked. However, if the method
call throws an {@link Error}, then it is recommended that processing of the notification
stop at that point, and if it is possible to propagate the {@code Error} to the sender of
the notification, this should be done.
New code should use the {@link NotificationEmitter} interface
instead.
Implementations of this interface and of {@code NotificationEmitter}
should be careful about synchronization. In particular, it is not a good
idea for an implementation to hold any locks while it is calling a
listener. To deal with the possibility that the list of listeners might
change while a notification is being dispatched, a good strategy is to
use a {@link CopyOnWriteArrayList} for this list. | 