Replacing AjaxFilter with MethodInterceptor

I wrote the previous posting without referring to DWR-Guice integration but in practice I extended org.directwebremoting.guice.AbstractDwrModule, not com.google.inject.AbstractModule.

For DWR-Guice users, the nice thing about injectable method interceptors is that you can use them to replace most uses of AjaxFilter, which is a good thing because the AjaxFilter support in the DWR-Guice stuff is weak (mea culpa).

I had to write some support utilities to get the right effect, but now I can do something like this:

bindInterceptor(
 subclassesOf(VulnerableService.class), // class matcher
 declaredBy(VulnerableService.class),   // method matcher
 // prevent nested interception
 outermostCall(new AuthenticationInterceptor()),
 outermostCall(new AuthorizationInterceptor())
);

and AuthenticationInterceptor is injected, so that it can look like
this:

class AuthenticationInterceptor 
    implements MethodInterceptor {
 @Inject Provider<RequestParameters> reqParmsProvider;
 @Inject Provider<AuthenticationService> authSvcProvider;
 public Object invoke(MethodInvocation invocation) 
     throws Throwable {
   RequestParameters reqParms = reqParmsProvider.get();
   AuthenticationService authSvc = authSvcProvider.get();
   if (authSvc.authenticate(reqParms))
     return invocation.proceed();
   else
     throw new AuthenticationException(reqParms);
 }
}

The subclassesOf matcher is part of Guice. The declaredBy matcher and the outermostCall interceptor decorator are custom implementations that I'll describe in a later posting.