Debugging: How to Attach to another application (closed source)

[MasterD]

Summary: I'm trying to debug modules, which are added to another application where the sources are not available.

A bit detail about my environment: Eclipse 3.4.2
About my app:
I have a main applikation where you can build plugins for (NO eclipse plugins). The main app is a bundle of some JAR files, whith a main method in one of the classes. When a plugin (basically another JAR file in a special folder) is added, this component is added to the main app without the need to recompile / have the sources of the main application.

I need to have it possible that the user, which builds the plugin, can debug it's plugin. Though he doesn't have the sources of the main application.

Edit: The target platform is Windows (XP) and Java SE Version 6.

[MasterD]

Have I explained my problem too diffuse? Do you need more information for an answer? Is this debugging task not possible? Do I have to closely read the eclipse documentation?

Please, this is really important to me.

[MasterD]

I was a bit off in to the wrong direction. I was already looking for a solution with the reflection api...

Solution is, in my case, quite simple:
Add the closed source jar files, start/debug the main application inside one of the jars, debug your plugin with breakpoints and everything :)