Which Java XML RPC library to use
I ended up going with with org.apache.xmlrpc, predominantly because my server does not send a WSDL file at all. This is not to say it would be impossible with JAX-WS. I am actually quite certain that JAX-WS is a more robust solution with many more features than Apache XMLRPC. However, the simple fact of the matter is I spent about 4 hours trying to implement user login to Drupal through JAX-WS with no results, after which I turned to Apache XMLRPC and had a working case in 10 minutes.