Open source is fine for this project. You may use unlimited amounts of open-source code without restriction.

I need a utility Java program to enable me to capture runtime method calls in a running application and automatically generate mock classes such as jmock / mockobjects / mockcreator / etc.

Those libraries such as jmock/mockobjects/mockcreator are very nice but they require the programmer to tediously hand-code all the mock call sequences. Since I already have a working application, I just need a utility to capture the run-time method call sequences via bytecode instrumentation and generate the mocks automatically.

As you may have surmised by now, I have a complex application already working but it has NO testcases, so I need a tool to automatically create the mocks in order for me to be able to create JUnit tests from scratch.

Obviously you will need to use BCEL or ASM3 or something similar for this. That is fine as I said, unlimited Open Source is allowed.