Really, building an AOP framework is a lot easier than you think. If you think about it, that's why there're so many of them out there right now; it's because it's really easy to write. One of the reasons for that is a new JBoss network project called Javassist. Javassist is out of the Tokyo Institute of Technology. It was written by a professor at the Tokyo Institute of Technology. What that library allows you to do is easily bytecode manipulate any class you want. So it's real easy to write an AOP framework on top of that.