First and foremost please don't scream "Use an IDE" at me. I have given eclipse a chance and it is... okay but I'm much faster in vim than eclipse.
Basically the one thing that I wish vim could do that eclipse does is syntax checking on the fly. In eclipse if you have a syntax error the line is given an error marker and the file-name at the top shows a little red thing to let you know there are errors. I have been trying to get this in vim. I've looked at syntastic (which doesn't have checkers for Java) but I can't seem to make it work. So the question remains...
Is there any way to check syntax every time I save a file with vim? Hopefully have it show up in the status line naming how many errors and what line the first error is on...
I haven't tried it and it's probably and overkill, but FYI there's the Eclim project which attempts to bring Eclipse's functionality to vim. It claims to do Java Validation along with many more features including code completion and code correction.