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第 36 章 Filters and Interceptors

36.1. Server Side Filters
36.1.1. Asynchronous filters
36.2. Client Side Filters
36.3. Reader and Writer Interceptors
36.4. Per Resource Method Filters and Interceptors
36.5. Ordering

JAX-RS 2.0 has two different concepts for interceptions: Filters and Interceptors. Filters are mainly used to modify or process incoming and outgoing request headers or response headers. They execute before and after request and response processing.

On the server-side you have two different types of filters. ContainerRequestFilters run before your JAX-RS resource method is invoked. ContainerResponseFilters run after your JAX-RS 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 JAX-RS 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, JAX-RS will run all ContainerResponseFilters. These filters allow you to modify the outgoing response before it is marshalling and sent to the client. So given all that, here's some pseudo code to give some understanding of how things work.

        // 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);
        }
    

It is possible to turn filters into asynchronous filters, if you need to suspend execution of your filter until a certain resource has become available. This turns the request asynchronous, but requires no change to your resource method declaration. In particular, synchronous and asynchronous resource methods continue to work as specified, regardless of whether or not a filter turned the request asynchronous. Similarly, one filter turning the request asynchronous requires no change in the declaration of further filters.

In order to turn a filter's execution asynchronous, you need to cast the ContainerRequestContext into a SuspendableContainerRequestContext (for pre/post request filters), or cast the ContainerResponseContext into a SuspendableContainerResponseContext (for response filters).

These context objects can turn the current filter's execution to asynchronous by calling the suspend() method. Once asynchronous, the filter chain is suspended, and will only resume after one of the following method is called on the context object:

abortWith(Response)
Terminate the filter chain, return the given Response to the client (only for ContainerRequestFilter).
resume()
Resume execution of the filter chain by calling the next filter.
resume(Throwable)
Abort execution of the filter chain by throwing the given exception. This behaves as if the filter were synchronous and threw the given exception.

You can also do async processing inside your AsyncWriterInterceptor (if you are using Async IO), which is the asynchronous-supporting equivalent to WriterInterceptor. In this case, you don't need to manually suspend or resume the request.

On the client side you also have two types of filters: ClientRequestFilter and ClientResponseFilter. ClientRequestFilters run before your 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 also allowed to abort the execute of the request and provide a canned response without going over the wire to the server. ClientResponseFilters can modfiy the Response object before it is handed back to application code. Here's some pseudo code to illustrate things.

            // 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, you can implement AsyncWriterInterceptor, which is a subtype of WriterInterceptor.

Sometimes you want a filter or interceptor to only run for a specific resource method. You can do this 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. You just use the Configurable interface to register the filters and interceptors you want for the specific resource method. @NameBinding works a lot like CDI interceptors. You annotate a custom annotation with @NameBinding and then apply that custom annotation to your 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 code 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 your filter or interceptor class.