Bumping an old thread...
There is a good example of how to do this at
http://www.mkyong.com/webservices/jax-rs/restful-java-client-with-jersey-client/
String input = "{\"singer\":\"Metallica\",\"title\":\"Fade To Black\"}";
ClientResponse response = webResource.type("application/json").post(ClientResponse.class, input);