Jdibug is a project mainly written in EMACS LISP and JAVA, it's free.
Fully elisp Java Debugger. Git clone of jdibug from http://jdibug.googlecode.com/svn
If you are running out of the subversion repository, you need to run "make" from the top level directory to generate all of the files that are needed.
As of version 0.4, jdibug also requires the CEDET is installed.