The org.zkoss.zk.ui.util.Monitor interface

Listener:

org.zkoss.zk.ui.util.Monitor interface

A listener could implement Monitor to monitor the statuses of ZK. Unlike other listener, there is at most one monitor listener for each Web application. If you like, you can chain them together manually.

ZK provides an implementation named Statistic, which accumulates the statistic data in the memory. It is a good starting point to understand the load of your ZK application.