One feature of WebLogic Server that helps developers to pinpoint class conflicts and other classloader issues is the Classloader Analysis Tool (CAT). Here's the description of what it does, taken from its main page:
CAT is a small web application that is designed to help application developers understand, analyze, and resolve classloading issues in their applications.
It does so by showing all applications and modules on the server where you're running CAT, and from there, you can drill down and check which classes were loaded by each classloader, searching for potential conflicts.
In order to use CAT, there are a few points that must be observed: