Jersey: JSR 311 Reference Implementation
Jersey (@ java.net) is the newly created open source JAX-RS (JSR 311) Reference Implementation for building RESTful Web services with plain old Java objects. But, it is also more than the Reference Implementation. Jersey aims to provide additional APIs and extension points (SPIs) so that developers may extend Jersey to suite their need.
Definitely worth spending time with if you’re doing REST and Java :-)