Add ExecutingResponseCreator

This commit adds a new `ResponseCreator` implementation that uses a
`ClientHttpRequestFactory` to perform an actual request.

Closes gh-29721

spring-test/src/main/java/org/springframework/test/web/client/response/ExecutingResponseCreator.java

@@ -0,0 +1,73 @@
+/*
+ * Copyright 2002-2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.test.web.client.response;
+
+import java.io.IOException;
+
+import org.springframework.http.client.ClientHttpRequest;
+import org.springframework.http.client.ClientHttpRequestFactory;
+import org.springframework.http.client.ClientHttpResponse;
+import org.springframework.mock.http.client.MockClientHttpRequest;
+import org.springframework.test.web.client.ResponseCreator;
+import org.springframework.util.Assert;
+import org.springframework.util.StreamUtils;
+
+/**
+ * A {@code ResponseCreator} which delegates to a {@link ClientHttpRequestFactory}
+ * to perform the request and return the associated response.
+ * This is notably useful when testing code that calls multiple remote services, some
+ * of which need to be actually called rather than further mocked.
+ * <p>Note that the input request is asserted to be a {@code MockClientHttpRequest} and
+ * the URI, method, headers and body are copied.
+ * <p>The factory can typically be obtained from a {@code RestTemplate} but in case this
+ * is used with e.g. {@code MockRestServiceServer}, make sure to capture the factory early
+ * before binding the mock server to the RestTemplate (as it replaces the factory):
+ * <pre><code>
+ * ResponseCreator withActualResponse = new ExecutingResponseCreator(restTemplate);
+ * MockRestServiceServer server = MockRestServiceServer.bindTo(restTemplate).build();
+ * //...
+ * server.expect(requestTo("/foo")).andRespond(withSuccess());
+ * server.expect(requestTo("/bar")).andRespond(withActualResponse);
+ * </code></pre>
+ *
+ * @author Simon Baslé
+ * @since 6.0.4
+ */
+public class ExecutingResponseCreator implements ResponseCreator {
+
+	private final ClientHttpRequestFactory requestFactory;
+
+
+	/**
+	 * Create a {@code ExecutingResponseCreator} from a {@code ClientHttpRequestFactory}.
+	 * @param requestFactory the request factory to delegate to
+	 */
+	public ExecutingResponseCreator(ClientHttpRequestFactory requestFactory) {
+		this.requestFactory = requestFactory;
+	}
+
+
+	@Override
+	public ClientHttpResponse createResponse(ClientHttpRequest request) throws IOException {
+		Assert.state(request instanceof MockClientHttpRequest, "Request should be an instance of MockClientHttpRequest");
+		MockClientHttpRequest mockRequest = (MockClientHttpRequest) request;
+		ClientHttpRequest newRequest = this.requestFactory.createRequest(mockRequest.getURI(), mockRequest.getMethod());
+		newRequest.getHeaders().putAll(mockRequest.getHeaders());
+		StreamUtils.copy(mockRequest.getBodyAsBytes(), newRequest.getBody());
+		return newRequest.execute();
+	}
+}

spring-test/src/main/java/org/springframework/test/web/client/response/MockRestResponseCreators.java

@@ -33,8 +33,15 @@ import org.springframework.test.web.client.ResponseCreator;
  * <p><strong>Eclipse users:</strong> consider adding this class as a Java editor
  * favorite. To navigate, open the Preferences and type "favorites".
  *
+ * <p>See also {@link ExecutingResponseCreator} for a {@code ResponseCreator} that is
+ * capable of performing an actual request. That case is not offered as a factory method
+ * here because of the early setup that is likely needed (capturing a request factory
+ * which wouldn't be available anymore when the factory methods are typically invoked,
+ * e.g. replaced in a {@code RestTemplate} by the {@code MockRestServiceServer}).
+ *
  * @author Rossen Stoyanchev
  * @since 3.2
+ * @see ExecutingResponseCreator
  */
 public abstract class MockRestResponseCreators {