One of the nicer features in eclipse is that it is able to automatically browse not only through your own sources, but through library sources as well, if they're available. But what if they're not?
In that case eclipse shows the class in a byte code view, with a button to attach a source .jar. Unfortunately it is often the case that you don't have the sources, either because they were not uploaded to maven central, or because they're closed altogether.
In any case, it is obviously often desirable while debugging to see what a library function actually expects, or why it fails. Contrary to popular belief, the actual code is always the ultimate documentation, because it's up to date even if human language docs are not.
So recently, while chasing after a Hans Moleman issue (more on that later), I needed sources from binary classes. Of course my first thought was 'decompiler', so I searched the eclipse marketplace for 'decompiler'.
I found JadClipse for eclipse 4.x, installed it, and voila: when I double click on a class file with no sources attached, the decompiler automatically decompiles it and shows me the source. Now that's what I call a plugin without hassle! That's a perfect counterpart to the -DdownloadSources flag for the maven eclipse mojo, now I never need to go without a library source again.