[Resteasy-developers] Interceptors

[Bill B. <bb...@re...>]

I'm currently prototyping some asynchronous jax-rs based on some of the 
asynchronous talk in the Restful Web Services book.  At first I 
implemented it in a non-abstract fashion.  Just brute force as I wanted 
to see what patterns came up.  After this I realized that I needed some 
form of interception to implement it.  (Mainly because of security).

So, for interception here's some ideas:

* Interceptors will be internal and not supported.  (I want us to write 
a few before we even allow users to try them out).

* interception would happen based on what additional annotation you 
provided: @BeforeUnmarshalling, @AfterUnmarshalling, @BeforeMarshalling, 
and @Aftermarshalling.

* Interceptors will not be called for any subresource locator methods.

* You would be able to use any JAX-RS annotation within the intercept 
method.

* It is an "around" pattern (like EJB's @AroundInvoke

interface RequestContext
{
    void invokeNext();
}

* You must inject and call invokeNext() on a RequestContext or no other 
interceptors will be called, and the request will not be dispatched.

* You will be able to inject the ResourceMethod object so you can get 
preprocessed information about the method you are invoking on 
(annotations, etc...)


So here's an example:

@Provider
@Interceptor
public class CacheControlInterceptor
{
    @BeforeUnmarshalling(@Context HttpRequest request,
                         @Context HttpResponse response,
                         @Context RequestContext ctx)
    {
       if (isCached(request)) {
         writeCachedResponse(request, response);
         return; // don't continue with dispatching
       }
       return invokeNext();
    }


    @BeforeMarshalling
    public void writeCacheControlHeaders(@Context HttpResponse response
                                         @Context RequestContext ctx)
    {
       ... write some cache control headers...
    }

    @AfterMarshalling
    public void grabBytesToMarshall(@Context HttpResponse response
                                    @Context RequestContext) {
    }
}



-- 
Bill Burke
JBoss, a division of Red Hat
http://bill.burkecentral.com