Update AsyncRestTemplate interception

AsyncRequestExecution now properly supports decoration of the
request (URI, HTTP method, and headers).

Removed a no-op IdentityListenableFutureAdapter.

Use Spring Framework coding style.

Issue: SPR-12538

spring-web/src/main/java/org/springframework/http/client/AsyncClientHttpRequestExecution.java

@@ -22,21 +22,28 @@
 import java.io.IOException;
 
 /**
- * The execution context of asynchronous client http request.
+ * Represents the context of a client-side HTTP request execution.
+ *
+ * <p>Used to invoke the next interceptor in the interceptor chain, or - if the
+ * calling interceptor is last - execute the request itself.
  *
  * @author Jakub Narloch
+ * @author Rossen Stoyanchev
+ * @since 4.3
  * @see AsyncClientHttpRequestInterceptor
  */
 public interface AsyncClientHttpRequestExecution {
 
     /**
-     * Resumes the request execution by invoking next interceptor in the chain or executing the
-     * request to the remote service.
+     * Resume the request execution by invoking next interceptor in the chain
+     * or executing the request to the remote service.
      *
      * @param request the http request, containing the http method and headers
      * @param body    the body of the request
      * @return the future
      * @throws IOException in case of I/O errors
      */
-    ListenableFuture<ClientHttpResponse> executeAsync(HttpRequest request, byte[] body) throws IOException;
-}
+    ListenableFuture<ClientHttpResponse> executeAsync(HttpRequest request, byte[] body)
+            throws IOException;
+
+}

spring-web/src/main/java/org/springframework/http/client/AsyncClientHttpRequestInterceptor.java

@@ -23,23 +23,52 @@
 import java.io.IOException;
 
 /**
- * The asynchronous HTTP request interceptor.
+ * Intercepts client-side HTTP requests. Implementations of this interface can be
+ * {@linkplain org.springframework.web.client.AsyncRestTemplate#setInterceptors(java.util.List)
+ * registered} with the {@link org.springframework.web.client.AsyncRestTemplate
+ * AsyncRestTemplate} as to modify the outgoing {@link HttpRequest} and/or
+ * register to modify the incoming {@link ClientHttpResponse} with help of a
+ * {@link org.springframework.util.concurrent.ListenableFutureAdapter
+ * ListenableFutureAdapter}.
+ *
+ * <p>The main entry point for interceptors is {@link #intercept}.
  *
  * @author Jakub Narloch
+ * @author Rossen Stoyanchev
+ * @since 4.3
  * @see org.springframework.web.client.AsyncRestTemplate
  * @see InterceptingAsyncHttpAccessor
  */
 public interface AsyncClientHttpRequestInterceptor {
 
     /**
-     * Intercepts the outgoing client HTTP request.
+     * Intercept the given request, and return a response future. The given
+     * {@link AsyncClientHttpRequestExecution} allows the interceptor to pass on
+     * the request to the next entity in the chain.
+     *
+     * <p>An implementation might follow this pattern:
+     * <ol>
+     * <li>Examine the {@linkplain HttpRequest request} and body</li>
+     * <li>Optionally {@linkplain org.springframework.http.client.support.HttpRequestWrapper
+     * wrap} the request to filter HTTP attributes.</li>
+     * <li>Optionally modify the body of the request.</li>
+     * <li>One of the following:
+     * <ul>
+     * <li>execute the request through {@link ClientHttpRequestExecution}</li>
+     * <li>don't execute the request to block the execution altogether</li>
+     * </ul>
+     * <li>Optionally adapt the response to filter HTTP attributes with the help of
+     * {@link org.springframework.util.concurrent.ListenableFutureAdapter
+     * ListenableFutureAdapter}.</li>
+     * </ol>
      *
-     * @param request   the request
-     * @param body      the request's body
-     * @param execution the request execution context
-     * @return the future
+     * @param request the request, containing method, URI, and headers
+     * @param body the body of the request
+     * @param execution the request execution
+     * @return the response future
      * @throws IOException in case of I/O errors
      */
-    ListenableFuture<ClientHttpResponse> interceptRequest(
-            HttpRequest request, byte[] body, AsyncClientHttpRequestExecution execution) throws IOException;
+    ListenableFuture<ClientHttpResponse> intercept(HttpRequest request, byte[] body,
+            AsyncClientHttpRequestExecution execution) throws IOException;
+
 }

spring-web/src/main/java/org/springframework/http/client/InterceptingAsyncClientHttpRequest.java

@@ -16,24 +16,23 @@
 
 package org.springframework.http.client;
 
+import java.io.IOException;
+import java.net.URI;
+import java.util.Iterator;
+import java.util.List;
+
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpRequest;
 import org.springframework.util.StreamUtils;
 import org.springframework.util.concurrent.ListenableFuture;
-import org.springframework.util.concurrent.ListenableFutureAdapter;
-
-import java.io.IOException;
-import java.net.URI;
-import java.util.Iterator;
-import java.util.List;
-import java.util.concurrent.ExecutionException;
 
 /**
- * A {@link AsyncClientHttpRequest} wrapper that enriches it proceeds the actual request execution with calling
- * the registered interceptors.
+ * An {@link AsyncClientHttpRequest} wrapper that enriches it proceeds the actual
+ * request execution with calling the registered interceptors.
  *
  * @author Jakub Narloch
+ * @author Rossen Stoyanchev
  * @see InterceptingAsyncClientHttpRequestFactory
  */
 class InterceptingAsyncClientHttpRequest extends AbstractBufferingAsyncClientHttpRequest {
@@ -46,6 +45,7 @@ class InterceptingAsyncClientHttpRequest extends AbstractBufferingAsyncClientHtt
 
     private HttpMethod httpMethod;
 
+
     /**
      * Creates new instance of {@link InterceptingAsyncClientHttpRequest}.
      *
@@ -55,17 +55,19 @@ class InterceptingAsyncClientHttpRequest extends AbstractBufferingAsyncClientHtt
      * @param httpMethod     the HTTP method
      */
     public InterceptingAsyncClientHttpRequest(AsyncClientHttpRequestFactory requestFactory,
-                                              List<AsyncClientHttpRequestInterceptor> interceptors, URI uri,
-                                              HttpMethod httpMethod) {
+            List<AsyncClientHttpRequestInterceptor> interceptors, URI uri, HttpMethod httpMethod) {
 
         this.requestFactory = requestFactory;
         this.interceptors = interceptors;
         this.uri = uri;
         this.httpMethod = httpMethod;
     }
 
+
     @Override
-    protected ListenableFuture<ClientHttpResponse> executeInternal(HttpHeaders headers, byte[] body) throws IOException {
+    protected ListenableFuture<ClientHttpResponse> executeInternal(HttpHeaders headers, byte[] body)
+            throws IOException {
+
         return new AsyncRequestExecution().executeAsync(this, body);
     }
 
@@ -79,37 +81,37 @@ public URI getURI() {
         return uri;
     }
 
+
     private class AsyncRequestExecution implements AsyncClientHttpRequestExecution {
 
-        private Iterator<AsyncClientHttpRequestInterceptor> nextInterceptor = interceptors.iterator();
+        private Iterator<AsyncClientHttpRequestInterceptor> iterator;
+
+        public AsyncRequestExecution() {
+            this.iterator = interceptors.iterator();
+        }
 
         @Override
-        public ListenableFuture<ClientHttpResponse> executeAsync(HttpRequest request, byte[] body) throws IOException {
-            if (nextInterceptor.hasNext()) {
-                AsyncClientHttpRequestInterceptor interceptor = nextInterceptor.next();
-                ListenableFuture<ClientHttpResponse> future = interceptor.interceptRequest(request, body, this);
-                return new IdentityListenableFutureAdapter<ClientHttpResponse>(future);
+        public ListenableFuture<ClientHttpResponse> executeAsync(HttpRequest request, byte[] body)
+                throws IOException {
+
+            if (this.iterator.hasNext()) {
+                AsyncClientHttpRequestInterceptor interceptor = this.iterator.next();
+                return interceptor.intercept(request, body, this);
             }
             else {
-                AsyncClientHttpRequest req = requestFactory.createAsyncRequest(uri, httpMethod);
-                req.getHeaders().putAll(getHeaders());
+                URI theUri = request.getURI();
+                HttpMethod theMethod = request.getMethod();
+                HttpHeaders theHeaders = request.getHeaders();
+
+                AsyncClientHttpRequest delegate = requestFactory.createAsyncRequest(theUri, theMethod);
+                delegate.getHeaders().putAll(theHeaders);
                 if (body.length > 0) {
-                    StreamUtils.copy(body, req.getBody());
+                    StreamUtils.copy(body, delegate.getBody());
                 }
-                return req.executeAsync();
+
+                return delegate.executeAsync();
             }
         }
     }
 
-    private static class IdentityListenableFutureAdapter<T> extends ListenableFutureAdapter<T, T> {
-
-        protected IdentityListenableFutureAdapter(ListenableFuture<T> adaptee) {
-            super(adaptee);
-        }
-
-        @Override
-        protected T adapt(T adapteeResult) throws ExecutionException {
-            return adapteeResult;
-        }
-    }
 }

spring-web/src/main/java/org/springframework/http/client/InterceptingAsyncClientHttpRequestFactory.java

@@ -16,17 +16,18 @@
 
 package org.springframework.http.client;
 
-import org.springframework.http.HttpMethod;
-
-import java.io.IOException;
 import java.net.URI;
 import java.util.Collections;
 import java.util.List;
 
+import org.springframework.http.HttpMethod;
+
 /**
- * The intercepting request factory.
+ * Wrapper for a {@link AsyncClientHttpRequestFactory} that has support for
+ * {@link AsyncClientHttpRequestInterceptor}s.
  *
  * @author Jakub Narloch
+ * @since 4.3
  * @see InterceptingAsyncClientHttpRequest
  */
 public class InterceptingAsyncClientHttpRequestFactory implements AsyncClientHttpRequestFactory {
@@ -35,22 +36,25 @@ public class InterceptingAsyncClientHttpRequestFactory implements AsyncClientHtt
 
     private List<AsyncClientHttpRequestInterceptor> interceptors;
 
+
     /**
-     * Creates new instance of {@link InterceptingAsyncClientHttpRequestFactory} with delegated request factory and
-     * list of interceptors.
+     * Create new instance of {@link InterceptingAsyncClientHttpRequestFactory}
+     * with delegated request factory and list of interceptors.
      *
-     * @param delegate     the delegated request factory
-     * @param interceptors the list of interceptors.
+     * @param delegate the request factory to delegate to
+     * @param interceptors the list of interceptors to use
      */
-    public InterceptingAsyncClientHttpRequestFactory(AsyncClientHttpRequestFactory delegate, List<AsyncClientHttpRequestInterceptor> interceptors) {
+    public InterceptingAsyncClientHttpRequestFactory(AsyncClientHttpRequestFactory delegate,
+            List<AsyncClientHttpRequestInterceptor> interceptors) {
 
         this.delegate = delegate;
-        this.interceptors = interceptors != null ? interceptors : Collections.<AsyncClientHttpRequestInterceptor>emptyList();
+        this.interceptors = (interceptors != null ? interceptors :
+                Collections.<AsyncClientHttpRequestInterceptor>emptyList());
     }
 
     @Override
-    public AsyncClientHttpRequest createAsyncRequest(URI uri, HttpMethod httpMethod) throws IOException {
-
-        return new InterceptingAsyncClientHttpRequest(delegate, interceptors, uri, httpMethod);
+    public AsyncClientHttpRequest createAsyncRequest(URI uri, HttpMethod method) {
+        return new InterceptingAsyncClientHttpRequest(this.delegate, this.interceptors, uri, method);
     }
+
 }

spring-web/src/main/java/org/springframework/http/client/support/InterceptingAsyncHttpAccessor.java

@@ -19,43 +19,50 @@
 import org.springframework.http.client.AsyncClientHttpRequestFactory;
 import org.springframework.http.client.AsyncClientHttpRequestInterceptor;
 import org.springframework.http.client.InterceptingAsyncClientHttpRequestFactory;
+import org.springframework.util.CollectionUtils;
 
 import java.util.ArrayList;
 import java.util.List;
 
 /**
- * The HTTP accessor that extends the base {@link AsyncHttpAccessor} with request intercepting functionality.
+ * The HTTP accessor that extends the base {@link AsyncHttpAccessor} with request
+ * intercepting functionality.
  *
  * @author Jakub Narloch
+ * @author Rossen Stoyanchev
+ * @since 4.3
  */
 public abstract class InterceptingAsyncHttpAccessor extends AsyncHttpAccessor {
 
-    private List<AsyncClientHttpRequestInterceptor> interceptors = new ArrayList<AsyncClientHttpRequestInterceptor>();
+    private List<AsyncClientHttpRequestInterceptor> interceptors =
+            new ArrayList<AsyncClientHttpRequestInterceptor>();
 
-    /**
-     * Retrieves the list of interceptors.
-     *
-     * @return the list of interceptors
-     */
-    public List<AsyncClientHttpRequestInterceptor> getInterceptors() {
-        return interceptors;
-    }
 
     /**
-     * Sets the list of interceptors.
+     * Sets the request interceptors that this accessor should use.
      *
      * @param interceptors the list of interceptors
      */
     public void setInterceptors(List<AsyncClientHttpRequestInterceptor> interceptors) {
         this.interceptors = interceptors;
     }
 
+    /**
+     * Return the request interceptor that this accessor uses.
+     */
+    public List<AsyncClientHttpRequestInterceptor> getInterceptors() {
+        return this.interceptors;
+    }
+
     @Override
     public AsyncClientHttpRequestFactory getAsyncRequestFactory() {
-        AsyncClientHttpRequestFactory asyncRequestFactory = super.getAsyncRequestFactory();
-        if(interceptors.isEmpty()) {
-            return asyncRequestFactory;
+        AsyncClientHttpRequestFactory delegate = super.getAsyncRequestFactory();
+        if (!CollectionUtils.isEmpty(getInterceptors())) {
+            return new InterceptingAsyncClientHttpRequestFactory(delegate, getInterceptors());
+        }
+        else {
+            return delegate;
         }
-        return new InterceptingAsyncClientHttpRequestFactory(asyncRequestFactory, getInterceptors());
     }
+
 }