IdeaJad lets you decompile Java jars or classes from IntelliJIdea 3.0.x & 4.x using Pavel Kouznetsov's decompiler JAD. The plugin offers support for Windows, Linux and MacOSX. It's open source and free.

Decompilation can be initiated manually through the context menu, or simply by navigating to a class file (e.g. CTRL-Click on a class or method name). Additionally, the built-in line sorter tries to re-arrange the decompiled class so that the decompiled source code line numbers match those of the original source code. This is quite useful for debugging.

Installation Notes

The last version available for manual installation is version 1162-2. It works with IntelliJIdea 4.0 (Aurora).

If you are using IntelliJIdea 4.0 or greater, please use IntelliJIdea's built-in Plugin Manager for downloading a suitable version of IdeaJad.

Just got to File->Settings->Plugins and click on the Available tab. After the list of available plugins has been downloaded, right-click on IdeaJad and choose Download and Install Plugin. After the installation you will have to restart IntelliJIdea.