MX4J is a project to build an Open Source implementation of the Java(TM) Management Extensions (JMX) and of the JMX Remote API (JSR 160) specifications, and to build tools relating to JMX.
JMX is an optional package for J2SE that provides a standard way to manage applications. It can also be used to wrap legacy systems and provide a standard interface to the outside world, enabling the development of web services. JMX allows developers to write more modular and loosely coupled system components and reduce the complexity of large, interoperating systems.
This implementation is used by Jetty, Tomcat, JOnAS, Geronimo and others