Open-source, free Java Decompiler

Is there any open source Java Decompilers for Ubuntu, preferably in the repositories and/or GPL'ed?

Both JAD and JD, the most popular decompilers I've found after a bit of googling, seems to be available only in binary form. And they are both proprietary.

It's hard to believe there is no such software in Ubuntu (or Linux in general).

If there is more than one, which you recommend, and why?

Solution 1:

Check out:

• Krakatau; the author is active on stackoverflow.com.
• CFR
• Procyon decompiler
• Fernflower and mirror

Solution 2:

• mstrobel/procyon's Java Decompiler, actively developed

Here's a recent discussion with participation from procyon's author (BonesJustice) and Krakatau's author (Uncaffeinated): http://www.reddit.com/r/ReverseEngineering/comments/1fb1to/new_open_source_java_decompiler/