Reverse "Correct generic type in BodyExtractor for form data"

This commit reverses 9efa976d31, and adds
code comments to highlight why some Body[Inserter|Extractor] instances
returned from Body[Inserters|Extractors] use
ServerHttp[Request|Response] instead of using
Reactive[Input|Output]Message.

spring-webflux/src/main/java/org/springframework/web/reactive/function/BodyExtractor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -27,6 +27,7 @@ import org.springframework.http.codec.HttpMessageReader;
  * A function that can extract data from a {@link ReactiveHttpInputMessage} body.
  *
  * @param <T> the type of data to extract
+ * @param <M> the type of {@link ReactiveHttpInputMessage} this extractor can be applied to
  * @author Arjen Poutsma
  * @since 5.0
  * @see BodyExtractors

spring-webflux/src/main/java/org/springframework/web/reactive/function/BodyExtractors.java

@@ -102,7 +102,10 @@ public abstract class BodyExtractors {
 	 * Return a {@code BodyExtractor} that reads form data into a {@link MultiValueMap}.
 	 * @return a {@code BodyExtractor} that reads form data
 	 */
-	public static BodyExtractor<Mono<MultiValueMap<String, String>>, ReactiveHttpInputMessage> toFormData() {
+	// Note that the returned BodyExtractor is parameterized to ServerHttpRequest, not
+	// ReactiveHttpInputMessage like other methods, since reading form data only typically happens on
+	// the server-side
+	public static BodyExtractor<Mono<MultiValueMap<String, String>>, ServerHttpRequest> toFormData() {
 		return (serverRequest, context) -> {
 					HttpMessageReader<MultiValueMap<String, String>> messageReader = formMessageReader(context);
 					return messageReader.readMono(FORM_TYPE, serverRequest, context.hints());

spring-webflux/src/main/java/org/springframework/web/reactive/function/BodyInserter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -28,6 +28,8 @@ import org.springframework.http.codec.HttpMessageWriter;
 /**
  * A combination of functions that can populate a {@link ReactiveHttpOutputMessage} body.
  *
+ * @param <T> the type of data to insert
+ * @param <M> the type of {@link ReactiveHttpOutputMessage} this inserter can be applied to
  * @author Arjen Poutsma
  * @since 5.0
  * @see BodyInserters

spring-webflux/src/main/java/org/springframework/web/reactive/function/BodyInserters.java

@@ -143,6 +143,9 @@ public abstract class BodyInserters {
 	 * @return a {@code BodyInserter} that writes a {@code ServerSentEvent} publisher
 	 * @see <a href="https://www.w3.org/TR/eventsource/">Server-Sent Events W3C recommendation</a>
 	 */
+	// Note that the returned BodyInserter is parameterized to ServerHttpResponse, not
+	// ReactiveHttpOutputMessage like other methods, since sending SSEs only typically happens on
+	// the server-side
 	public static <T, S extends Publisher<ServerSentEvent<T>>> BodyInserter<S, ServerHttpResponse> fromServerSentEvents(
 			S eventsPublisher) {
 
@@ -165,6 +168,9 @@ public abstract class BodyInserters {
 	 * Server-Sent Events
 	 * @see <a href="https://www.w3.org/TR/eventsource/">Server-Sent Events W3C recommendation</a>
 	 */
+	// Note that the returned BodyInserter is parameterized to ServerHttpResponse, not
+	// ReactiveHttpOutputMessage like other methods, since sending SSEs only typically happens on
+	// the server-side
 	public static <T, S extends Publisher<T>> BodyInserter<S, ServerHttpResponse> fromServerSentEvents(S eventsPublisher,
 			Class<T> eventClass) {
 
@@ -183,6 +189,9 @@ public abstract class BodyInserters {
 	 * Server-Sent Events
 	 * @see <a href="https://www.w3.org/TR/eventsource/">Server-Sent Events W3C recommendation</a>
 	 */
+	// Note that the returned BodyInserter is parameterized to ServerHttpResponse, not
+	// ReactiveHttpOutputMessage like other methods, since sending SSEs only typically happens on
+	// the server-side
 	public static <T, S extends Publisher<T>> BodyInserter<S, ServerHttpResponse> fromServerSentEvents(S eventsPublisher,
 			ResolvableType eventType) {
 

spring-webflux/src/test/java/org/springframework/web/reactive/function/BodyExtractorsTests.java

@@ -207,7 +207,7 @@ public class BodyExtractorsTests {
 
 	@Test
 	public void toFormData() throws Exception {
-		BodyExtractor<Mono<MultiValueMap<String, String>>, ReactiveHttpInputMessage> extractor = BodyExtractors.toFormData();
+		BodyExtractor<Mono<MultiValueMap<String, String>>, ServerHttpRequest> extractor = BodyExtractors.toFormData();
 
 		DefaultDataBufferFactory factory = new DefaultDataBufferFactory();
 		DefaultDataBuffer dataBuffer =