Yes, I've stumbled accross that a couple of times looking for a solution (with slight variations). It's a tad hacky what with relying on the system classloader to be a URLClassLoader but it does work rather nicely. I'm hoping that the Webstart classloader is also an URLClassLoader as well.
The 'proper' solution to what I'm after is supposed to be with a custom ClassLoader which checks my own resource locations. Unfortunatly the delagation method only checks a custom loader *after* the system classloader has failed to find something. But because an external class gets loaded fine with the system classloader it doesn't check 'further down' the delagation order and so my new loader never even gets a look in. I suspect to do that properly I'd have to re-implement an *entire* ClassLoader myself (effectivly ignoring the delagation method and going back to Java 1.1 classloader interface) but that's not something I particularly want to waste time doing.
So...just to check...that adds any arbitrary class accessible via any URL (file, http, etc) using the system classloader, so that you don't get any problems with classloader-spaces causing class/class compares to fail for identical classes?
Seems to, as you never add any additional loaders - you just extend the search paths for the existing one.