Sorry, I think your question needs more context. FYI the first thing that I though on seeing the word "applet" is that you were on a Mac, in which case an appropriate link would be here.

But it was pointed out in chatter that you are probably thinking Java applets. In that case some details about your situation are probably important. The odds are that either you are dealing with a webpage (in which case I would talk to the applet with JavaScript) or else you want to talk over a socket in which case you want to look for general client-server links (which there are plenty of) for both Java and Perl. From the point of view of both Java and Perl if you are using a socket the fact that the other side is written in a different language is irrelevant.

I am sure that there is some other work on integrating Java and Perl, but I am not familiar with it.

Anyways, if you formulate a question with more context and you are likely to get a better answer.