Process custom annotation in implementing class of an Resource interface - jax-rs

Question

I am trying to process a custom annotation on a class that implements an external interface that defines a Resource. The setup is the following:
A Resource interface, I can't modify it:
#Path("/v1")
public interface Resource {
#GET
#Path("/foo")
Response foo();
}
An implementation that I can modify:
public class ResourceImpl implements Resource {
#Override
#CustomAnnotation // has Retention.RUNTIME
public Response foo() {
// foo logic
}
}
I've implemented a filter to try and process the #CustomAnnotation on the overriden foo() method:
#Provider
#ServerInterceptor
#Precedence("SECURITY")
public class CustomAnnotationInterceptor implements ContainerRequestFilter {
#Context
ResourceInfo resourceInfo;
#Override
public void filter(ContainerRequestContext containerRequestContext) throws IOException {
// check if the invoked resource method is annotated with #CustomAnnotation and do logic
}
}
However, when I try to get the matched resource class from the ResourceInfo instance, I get the Resource interface, and when I get the matched method, I get the foo() method from the interface which is lacking the #CustomAnnotation. Is there any way around this?
I'm using RESTEasy as an implementation of JAX-RS.

Answer 1

You could implement an interceptor, where you can get hold of the actual resource (method and class) being called. The interceptor should be bound to your annotation using #InterceptorBinding (see 54.2.4 Binding Interceptors to Components).
// Interceptor
#Interceptor
#CustomAnnotation
#Priority(Interceptor.Priority.APPLICATION)
public class CustomAnnotationInterceptor {
#AroundInvoke
public Object interceptCustomAnnotation(InvocationContext ctx) throws Exception {
CustomAnnotation customAnnotation = null;
// The actual method being called
Method method = ctx.getMethod();
if (method != null) {
customAnnotation = method.getAnnotation(CustomAnnotation.class);
}
// ... do stuff with the annotation
return ctx.proceed();
}
}
To get the instance of the class that implements your interface you could use ctx.getMethod().getDeclaringClass() or ctx.getTarget().getClass().getSuperclass().