finding a class inside a jar file

[Phaelax]

I want to add theme support to my program so that users can just download jar files containing a LnF and just drop it into an extension directory or whereever. I'll just scan that directory for jar files to see which are present. Is there a way search for a class type in a jar file and retrieve its class name? I know the UIManager class can retrieve a list of installed LnF classes, but the user-downloaded ones aren't exactly installed.