Add WebResponseExtractor impl for RxJava1

This commit adds `RxJava1WebResponseExtractors`, a static factory of
`WebResponseExtractor`s that are based on the RxJava1 composition API.
All extracted types are based on the `Single` and `Observable` types.

spring-web-reactive/src/main/java/org/springframework/web/client/reactive/RxJava1WebResponseExtractors.java

@@ -0,0 +1,131 @@
+/*
+ * Copyright 2002-2016 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
+ *
+ *      http://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.web.client.reactive;
+
+import java.nio.charset.Charset;
+import java.util.List;
+import java.util.Optional;
+
+import reactor.core.converter.RxJava1ObservableConverter;
+import reactor.core.converter.RxJava1SingleConverter;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+import rx.Observable;
+import rx.Single;
+
+import org.springframework.core.ResolvableType;
+import org.springframework.core.codec.Decoder;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.MediaType;
+import org.springframework.http.ResponseEntity;
+import org.springframework.http.client.reactive.ClientHttpResponse;
+
+/**
+ * Static factory methods for {@link WebResponseExtractor}
+ * based on the {@link Observable} and {@link Single} API.
+ *
+ * @author Brian Clozel
+ */
+public class RxJava1WebResponseExtractors {
+
+	private static final Charset UTF_8 = Charset.forName("UTF-8");
+
+	private static final Object[] HINTS = new Object[] {UTF_8};
+
+	/**
+	 * Extract the response body and decode it, returning it as a {@code Single<T>}
+	 */
+	public static <T> WebResponseExtractor<Single<T>> body(Class<T> sourceClass) {
+
+		ResolvableType resolvableType = ResolvableType.forClass(sourceClass);
+		//noinspection unchecked
+		return webResponse -> (Single<T>) RxJava1SingleConverter.from(webResponse.getClientResponse()
+				.flatMap(resp -> decodeResponseBody(resp, resolvableType, webResponse.getMessageDecoders()))
+				.next());
+	}
+
+	/**
+	 * Extract the response body and decode it, returning it as an {@code Observable<T>}
+	 */
+	public static <T> WebResponseExtractor<Observable<T>> bodyStream(Class<T> sourceClass) {
+
+		ResolvableType resolvableType = ResolvableType.forClass(sourceClass);
+		return webResponse -> RxJava1ObservableConverter.from(webResponse.getClientResponse()
+				.flatMap(resp -> decodeResponseBody(resp, resolvableType, webResponse.getMessageDecoders())));
+	}
+
+	/**
+	 * Extract the full response body as a {@code ResponseEntity}
+	 * with its body decoded as a single type {@code T}
+	 */
+	public static <T> WebResponseExtractor<Single<ResponseEntity<T>>> response(Class<T> sourceClass) {
+
+		ResolvableType resolvableType = ResolvableType.forClass(sourceClass);
+		return webResponse -> (Single<ResponseEntity<T>>)
+				RxJava1SingleConverter.from(webResponse.getClientResponse()
+						.then(response ->
+								Mono.when(
+										decodeResponseBody(response, resolvableType, webResponse.getMessageDecoders()).next(),
+										Mono.just(response.getHeaders()),
+										Mono.just(response.getStatusCode())))
+						.map(tuple -> {
+							//noinspection unchecked
+							return new ResponseEntity<>((T) tuple.getT1(), tuple.getT2(), tuple.getT3());
+						}));
+	}
+
+	/**
+	 * Extract the full response body as a {@code ResponseEntity}
+	 * with its body decoded as an {@code Observable<T>}
+	 */
+	public static <T> WebResponseExtractor<Single<ResponseEntity<Observable<T>>>> responseStream(Class<T> sourceClass) {
+		ResolvableType resolvableType = ResolvableType.forClass(sourceClass);
+		return webResponse -> RxJava1SingleConverter.from(webResponse.getClientResponse()
+				.map(response -> new ResponseEntity<>(
+						RxJava1ObservableConverter
+								.from(decodeResponseBody(response, resolvableType, webResponse.getMessageDecoders())),
+						response.getHeaders(),
+						response.getStatusCode())));
+	}
+
+	/**
+	 * Extract the response headers as an {@code HttpHeaders} instance
+	 */
+	public static WebResponseExtractor<Single<HttpHeaders>> headers() {
+		return webResponse -> RxJava1SingleConverter
+				.from(webResponse.getClientResponse().map(resp -> resp.getHeaders()));
+	}
+
+	protected static <T> Flux<T> decodeResponseBody(ClientHttpResponse response, ResolvableType responseType,
+			List<Decoder<?>> messageDecoders) {
+
+		MediaType contentType = response.getHeaders().getContentType();
+		Optional<Decoder<?>> decoder = resolveDecoder(messageDecoders, responseType, contentType);
+		if (!decoder.isPresent()) {
+			return Flux.error(new IllegalStateException("Could not decode response body of type '" + contentType +
+					"' with target type '" + responseType.toString() + "'"));
+		}
+		//noinspection unchecked
+		return (Flux<T>) decoder.get().decode(response.getBody(), responseType, contentType, HINTS);
+	}
+
+
+	protected static Optional<Decoder<?>> resolveDecoder(List<Decoder<?>> messageDecoders, ResolvableType type,
+			MediaType mediaType) {
+		return messageDecoders.stream().filter(e -> e.canDecode(type, mediaType)).findFirst();
+	}
+}