I\'m starting a project using a Restful architecture implemented in Java (using the new JAX-RS standard)
We are planning to develop the GUI with a Flex application.
RestfulX has solved most/all of the REST problems with Flex. It has support for Rails/GAE/Merb/CouchDB/AIR/WebKit, and I'm sure it would be a snap to connect it to your Java implementation.
Dima's integrated the AS3HTTPClient Library into it also.
Check it out!