Thanks arne-bab!

In fact, If I'm not missing something, limewire and phex aren't structured as APIs.

Every source archive comes with a predefined folder structure, and related (ant) build files, which are focused on building a new phex-limewire client, with the specification given by their own community.
What I need is a library, a bounch of packages which I can add easily to my java package collection, and extracting them from a pre- existing project can be painful, because they rely on specific build files to be compiled, and aren't meant to be imported to other projects without them.

The only library I 've been able to import so far was Jtella but, as I said before, it seems too old to work with, though it's a small academic project.