Wow! Finally some bits available to DTrace Java. Imagine you can trace Java methods similar way as C functions with PID provider! And correlate them to syscalls, in-kernel functions, IOs, etc... Whole bunch of profiling is now possible. Although it looks like it's not perfect (yet) it's definitely worth looking into.
You can find some examples on Bryan's and Adam's blogs.
You can download Java provider for DTrace from project page. I'm sure Java developers will love it!
btw: this is available under CDDL!