What Java WebDAV client side library could you recommend?
OK I'm a bit late, but you really should check out the milton webdav server project. Its open source (apache2), mature and is actively maintained.
Its designed to allow any backend implementation to be hooked up to webdav, and many users have reported implementing it in under 4 hours for existing applications.
It supports all the usual webdav stuff like locking, custom properties, digest/basic authentication, etc. It also supports caldav and integrated with apache FTP so you get 2 protocols for the price of one!
Milton ships with a servlet and a spring controller, and it can run independently of a web container.
Milton also has a nice little webdav client library, which is ideal for desktop apps due to its observer support.