With JAX-RS 2.0 client you can access whatever backend you like--it only has to speak HTTP. So you can use JAX-RS 2.0 client now from Java clients or to drive system tests:
NEW workshop: Building HTML 5 Applications With Angular 2
Full week in December 2016: from Java EE 7 Bootstrap, Effective, Architectures over Testing to Microservices
On demand workshops: Java EE 7: Bootstrap, Effective, Testing and Microservices available for streaming.