For a current project, I was thinking of implementing WebDAV to present a virtual file store that clients can access. I have only done Google research so far but it looks like I
If you run Apache Jackrabbit under, say, Tomcat, it can be configured to offer WebDAV and store uploaded files. Perhaps that will be a useful model, or even a good enough replacement for the planned implementation.
Apache Jackrabbit Support for WebDAV
Also, you may want to be aware of the BitKinex client (free 30 day trial), which I have found to be a useful tool for testing a WebDAV server.
BitKinex Home Page