This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
JMX (Java Management Extensions) is an API for exposing a management interface of a component/application/device in a standard, platform-independent way. The core of JMX are the things called MBeans. MBeans are objects that implement one of the standard javax.management.*MBean interfaces. For example, I could write an MBean implementation for an EJB which would allow tweaking certain properties of the EJB at runtime (such as the location of a file, the timeout for obtaining a connection to system X, the algorithm to use for doing foo, etc.). Start by reading the sample chapter from JMX in Action.