I'd say it largely depends on the environment where your application should run. Should it be a Java standalone application? Running inside a
Servlet container? Inside an application server? OSGi container?
There are many frameworks and tools to support the implementation of REST webservices. Depending on the mentioned environments or platforms there may be out-of-the-box support for REST. For standalone applications
JBoss RESTEasy or the Restlet framework may be good candidates. Many web frameworks allow to implement REST services without additional frameworks. The
JEE platform has built-in support in the form of the JAX-RS API. There are more than enough tools and frameworks. I think the bigger challenge is how to design a good web API which is really RESTful.
@Ulf: It's not uncommon to use the Atom format or something like that as a media type for REST resources. I guess that's what the OP meant.
Marco