Here's an early experimental client I had played around with a while back. It supports getInfo, getBalance and getNewAddress, and can easily be expanded. In order to run it, the credentials for your local bitcoind have to match the values in the client class:

httpclient.getCredentialsProvider().setCredentials(new AuthScope("localhost", 8332), new UsernamePasswordCredentials("btc", "123"));

Feel free to use this code in any way, but understand that it's only 5 minutes of work on a start, not a realistic client implementation. Hope it helps you generate some ideas!