Chapter 35. Filters and Interceptors

On the server-side there are two different types of filters. ContainerRequestFilters run before a Jakarta RESTful Web Services resource method is invoked. ContainerResponseFilters run after a Jakarta RESTful Web Services resource method is invoked. As an added caveat, ContainerRequestFilters come in two flavors: pre-match and post-matching. Pre-matching ContainerRequestFilters are designated with the @PreMatching annotation and will execute before the Jakarta RESTful Web Services resource method is matched with the incoming HTTP request. Pre-matching filters often are used to modify request attributes to change how it matches to a specific resource method (i.e. strip .xml and add an Accept header). ContainerRequestFilters can abort the request by calling ContainerRequestContext.abortWith(Response). A filter might want to abort if it implements a custom authentication protocol.

After the resource class method is executed, Jakarta RESTful Web Services will run all ContainerResponseFilters. These filters allow the outgoing response to be modified before it is marshalling and sent to the client. Here is some pseudocode to give some understanding of how it works.

        // execute pre match filters
        for (ContainerRequestFilter filter : preMatchFilters) {
            filter.filter(requestContext);
            if (isAborted(requestContext)) {
               sendAbortionToClient(requestContext);
               return;
            }
        }
        // match the HTTP request to a resource class and method
        JaxrsMethod method = matchMethod(requestContext);

        // Execute post match filters
        for (ContainerRequestFilter filter : postMatchFilters) {
           filter.filter(requestContext);
           if (isAborted(requestContext)) {
              sendAbortionToClient(requestContext);
              return;
           }
        }

        // execute resource class method
        method.execute(request);

        // execute response filters
        for (ContainerResponseFilter filter : responseFilters) {
           filter.filter(requestContext, responseContext);
        }
    

The client side also has two types of filters: ClientRequestFilter and ClientResponseFilter. ClientRequestFilters run before an HTTP request is sent over the wire to the server. ClientResponseFilters run after a response is received from the server, but before the response body is unmarshalled. ClientRequestFilters are allowed to abort the execution of the request and provide a canned response without going over the wire to the server. ClientResponseFilters can modify the Response object before it is handed back to application code. Here's pseudocode to illustrate this.

            // execute request filters
            for (ClientRequestFilter filter : requestFilters) {
               filter.filter(requestContext);
               if (isAborted(requestContext)) {
                  return requestContext.getAbortedResponseObject();
               }
            }

            // send request over the wire
            response = sendRequest(request);

            // execute response filters
            for (ClientResponseFilter filter : responseFilters) {
               filter.filter(requestContext, responseContext);
            }
        

While filters modify request or response headers, interceptors deal with message bodies. Interceptors are executed in the same call stack as their corresponding reader or writer. ReaderInterceptors wrap around the execution of MessageBodyReaders. WriterInterceptors wrap around the execution of MessageBodyWriters. They can be used to implement a specific content-encoding. They can be used to generate digital signatures or to post or pre-process a Java object model before or after it is marshalled.

Note that in order to support Async IO, AsyncWriterInterceptor can be implemented, which is a subtype of WriterInterceptor.

Sometimes it is desired to have a filter or interceptor only run for a specific resource method. This can be done in two different ways: register an implementation of DynamicFeature or use the @NameBinding annotation. The DynamicFeature interface is executed at deployment time for each resource method. Use the Configurable interface to register the filters and interceptors wanted for the specific resource method. @NameBinding works a lot like CDI interceptors. Annotate a custom annotation with @NameBinding and then apply that custom annotation to the filter and resource method. The custom annotation must use @Retention(RetentionPolicy.RUNTIME) in order for the attribute to be picked up by the RESTEasy runtime when it is deployed.

            @NameBinding
            @Retention(RetentionPolicy.RUNTIME)
            public @interface DoIt {}

            @DoIt
            public class MyFilter implements ContainerRequestFilter {...}

            @Path("/root")
            public class MyResource {

               @GET
               @DoIt
               public String get() {...}
            }
        

Ordering is accomplished by using the @BindingPriority annotation on the filter or interceptor classes.