there are a number of Java debugging  tools, but the top one is
Jprofiler, see following link and download the evaluation copy.
www.ej-technologies.com/.../overview.html

Also Jbuilder has its own classic debugger but I will prefer Jprofiler as I
am using it and it has no match, only one issue is that it requires huge
memory and other resources, but once you are in the production level
debugging or memory leaks, or dead locks you pay for resources without any
hesitation.