What Java CMIS client library should I use?

Answer 1

I recommend OpenCMIS. (Well, I have to since I'm involved in the project.) It's an active project supported by a broad community. OpenCMIS supports both bindings, AtomPub and Web Services, and has been tested against a number of repositories.

chemistry-atompub-client has been abandoned and chemistry-abdera is not very active. You can, of course, handle the AtomPub binding directly, but that's a lot of work.