Getting threaddump of a Java Process.

Analyzing thread dump is the best way to debug a hanging process.
There are 3 ways to get it.

1. Issue kill -9 command.
For ex: If you have started a Sun Web Server process and if it is hanging because of an web-app deployed in it, you can issue command kill -9 pid where pid is the process id of the child process. Note that there will be two processes. You need to issue this on child process id.

2. Attaching jdb. Refer to the following document for more details.
http://wiki.caucho.com/Thread_dump

3. Using JHAT tool. You need to start web server with JDK 1.6 and above to use this. This can be set in the server.xml file for the variable JAVA_HOME. JHAT is a heap analyzer tool which will give you all info related to the heap of the process in the process address space.