Well, I know I've seen CPAN modules to put Java inside Perl, for instance Java, which makes calls to a running JVM. You might be able to use some of the code from there -- write a separate JavaServer class which takes calls from Jakarta and passes them to a Java object which you've instantiated using Java and mod_perl which then gets polled for events from Perl and has the appropriate Perl code executed...

Then again, maybe not.