title: What's a JAX-RS implementation?
body: <p>I have been trying to figure out how to use JAX-RS for quite some time. I started from the very basic concepts and then to gradually understand the annotation styled programming, the meaning of @Path, @Get, @Post, etc.</p>
  
  <p>To my understanding, as to what has been mentioned in a lot of places, JAX-RS is a framework that focuses on applying Java annotations to plain Java objects (Page 27, Bill Burke, RESTful Java).</p>
  
  <p>I have then got confused beyond this point. If JAX-RS in itself is a framework that defines APIs dealing with annotations in order to implement RESTful web service, what's the meaning of "implementation of JAX-RS" such as "Jersey" and "JBoos Resteasy". Another layer on top of JAX-RS? Why do we need them?</p>
  
  <p>Could someone provide me some insights about it? Many thanks!!!</p>