The org.zkoss.zk.ui.util.WebAppInit interface
A listener could implement WebAppInit to initialize a ZK application when it has been loaded.
When a ZK application has been loaded, it invokes the
init method of this interface such that developers could plug the application-specific codes to initialize the application.
Instantiation: An independent instance of the given class is instantiated each time before the method is invoked. It means it is thread safe, and all information stored in non-static members will be lost after called.