You can now download Java::Javap from CPAN to get the java2perl6 command line tool (javap is the standard java decompilation tool). This is not a finished product. The script will work on Java interfaces (classes are not yet supported properly). Output dumps to the screen. That output is a Perl 6 role for the java interface.
I need to learn enough about Perl 6 classes to generate proper output before supporting classes. In the mean time I plan to add support for controlling where output goes and for recursing through encountered types. For instance, if a method in class org.example.Useless returns an object of type org.example.Useless.Helper, recursing would process Helper after Useless processing finished.
I will also be heading to YAPC a week from tomorrow, so I'm putting some work into my talk on our shop's web framework called Gantry.