Streaming JSON (or any other content) with JAX-RS 2.0 is really easy to implement with the helper interface StreamingOutput:
I was asked the question "How to stream content with JAX-RS 2.0?" during the recent Warsaw JUG (wjug at twitter) meeting: Unorthodox Enterprise Practices. We were over time and the JUG leader repeatedly reminded me about this fact, so I rejected to answer this question. Now, as usual, or questions remain answered :-)
See you at Java EE Workshops at MUC Airport!
NEW: Effective Java EE 7 -- Available For Streaming