directory listing in core protocol

[Ben Tatham]

Hello All,
Is it possible to get a directory listing of files from the core 
protocol?  Currently, I can't even getClass().getResource() to return a 
valid URL for a directory, but it does work if I specify a file. 

For example, if I have the following in my jar when I compile

foo
   - someResource.txt
   adir
      - a.txt
      - b.txt

I can get an URL for foo/someResource.txt, and I can open an InputStream 
and get the contents.
But if I try getClass().getResource("/foo/adir"), I get null.

Thanks,
Ben