ZK Developer's Reference/Customization/Life Cycle Listener

You could have some custom initialization and cleanup when an application, a session, a desktop or an execution is instantiated or about to be destroyed.

There are two steps:

1. Implements the corresponding interface. For example, WebAppInit for application's initialization
2. Register it in WEB-INF/zk.xml, or in Java.

Interfaces

Task	Interface
Application Init	WebAppInit
Application Cleanup	WebAppCleanup
Session Init	SessionInit
Session Cleanup	SessionCleanup
Desktop Init	DesktopInit
Desktop Cleanup	DesktopCleanup
Execution Init	ExecutionInit
Execution Cleanup	ExecutionCleanup

Notice that ZK will instantiate an object from the class you registered for each callback. For example, an object is instantiated to invoke DesktopInit.init(Desktop, Object), and another object instantiated to invoke DesktopCleanup.cleanup(Desktop), even if you register a class that implements both DesktopInit and DesktopCleanup.

If you have something that is initialized in the init callback and have to clean it up in the cleanup callback, you cannot store it as a data member. Rather, you have to maintain it by yourself, such as storing it in the desktop's attributes (Desktop.setAttribute(String, Object)), session's attributes or application's attributes.

Registration

The registration in WEB-INF/zk.xml is the same, no matter what interface you implement:

<listener>
    <listener-class>my.MyImplementation</listener-class>
</listener>

The registration in Java is done by Configuration.addListener(Class).

webapp.getConfiguration().addListener(my.MyImplementation.class);