I have a JAX-RS REST service implemented using Jersey. One of the cool features of JAX-RS/Jersey is how easily a POJO can be turned into a REST service, simply by sprinkling
Here's a simple brief example of using JAXB to map objects to JSON (using Jackson):
http://ondra.zizka.cz/stranky/programovani/java/jaxb-json-jackson-howto.texy