Creating Event Listeners

An event listener gathers statistics from events that an event provider sends. To enable an add-on component to gather statistics from events, create listeners to receive events from the event provider. The listener can receive events from the add-on component in which the listener is created and from other components.

To create an event listener, write a Java class to represent the listener. The listener can be any Java object.

Ensure that the class that you write meets these requirements:

• The return value of all callback methods in the listener must be void.

• Because the methods of your event provider class may be entered by multiple threads, the listener must be thread safe.

• The listener must have the same restrictions as a Java Platform, Enterprise Edition (Java EE) application. For example, the listener cannot open server sockets, or create threads.

A listener is called in the same thread as the event method. As a result, the listener can use thread locals. If the monitored system allows access to thread locals, the listener can access thread locals of the monitored system.

A listener that is not registered to listen for events is never called by the framework. Therefore, unregistered listeners do not consume any computing resources, such as memory or processor cycles.