I work for Empirix, a test tool company. We make three tools for testing J2EE applications:
1. Bean-test ... performance and functional testing of EJBs.
2. FirstACT ... performance and functional testing of Web Services.
3. e-Test Suite ... performance and functional testing of web applications (eg: JSPs)
We are having web events this month talking EJB testing, web services testing, and so on. To read about them, check out:
So that this is not a complete info-mercial, there are good profiler tools out there (JProbe, etc) that are good for finding memory leaks and can be used for J2EE.
JUnit is free-ware tool and is used functional testing only (not performance testing).