It can run in any Servlet container.
While JAX-RS is only a server-side specification, RESTEasy has innovated to bring JAX-RS to the client through the RESTEasy JAX-RS Client Framework.
This client-side framework allows to map outgoing HTTP requests to remote servers using JAX-RS annotations and interface proxies.
Here are some key features of "RESTEasy":
· Fully certified JAX-RS implementation
· Portable to any app-server/Tomcat that runs on JDK 5 or higher
· Embeddedable server implementation for junit testing
· Client framework that leverages JAX-RS annotations so that you can write HTTP clients easily (JAX-RS only defines server bindings)
· Client "Browser" cache. Supports HTTP 1.1 caching semantics including cache revalidation
· Server in-memory cache. Local response cache. Automatically handles ETag generation and cache revalidation
· Rich set of providers for: XML, JSON, YAML, Fastinfoset, Multipart, XOP, Atom, etc.
· JAXB marshalling into XML, JSON, Jackson, Fastinfoset, and Atom as well as wrappers for maps, arrays, lists, and sets of JAXB Objects.
· GZIP content-encoding. Automatic GZIP compression/decompression suppport in client and server frameworks
· Asynchronous HTTP (Comet) abstractions for JBoss Web, Tomcat 6, and Servlet 3.0
· Asynchronous Job Service.
· Rich interceptor model.
· EJB, Seam, Guice, Spring, and Spring MVC integration.