JConsole

Java SE 5.0 added support for monitoring and management of Java applications,
allowing the installation of agents in the virtual machine that track memory consumption,
thread usage, class loading, and so on. This feature is particularly important
for large and long-running Java programs such as application servers. As a
demonstration of these capabilities, the JDK ships with a graphical tool called jconsole
that displays statistics about the performance of a virtual machine (see Figure
11–3). Find out the ID of the operating system process that runs the virtual machine.
In UNIX/Linux, run the ps utility; in Windows, use the task manager. Then launch
the jconsole program:
jconsole processID
The console gives you a wealth of information about your running program. See
http://java.sun.com/developer/technicalArticles/J2SE/jconsole.html for more information.