One interesting question I had at my Java 7 talk this past weekend was whether JSR 203 would support an in-memory virtual filesystem. Interestingly, this is exactly the same question the first time I read the JSR 203 spec. A virtual filesystem will not be included as part of JSR 203 but certainly the API is designed to be extensible and all of the hooks exist to provide such an implementation.
Alan Bateman mentioned that using direct buffers for file storage would be an excellent choice as it would provide for large virtual file systems without actually using large amounts of Java heap.
So, if anyone’s looking for a cool (and useful) open source project, this would be a great one. Having a virtual memory system to plug into would be fantastic for unit testing. You could create files to your heart’s content and the file access would be fast while also saving you from all the annoying issues with deleting temporary files, Windows file locking, etc. Go to it, lazyweb!