Fix @RequestBody(required=false) support

Prior to this commit, requests with an empty body and no Content-Type
header set would fail with a HttpMediaTypeNotSupportedException when
mapped to a Controller method argument annotated with
@RequestBody(required=false).
In those cases, the server implementation considers with an
"application/octet-stream" content type and polls messageconverters for
conversion. If no messageconverter is able to process this request, a
HttpMediaTypeNotSupportedException is thrown.

This change makes sure that such exceptions are not thrown if the
incoming request has:
* no body
* no content-type header

In this case, a null value is returned.

Issue: SPR-13147

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/AbstractMessageConverterMethodArgumentResolver.java

@@ -158,6 +158,7 @@ public abstract class AbstractMessageConverterMethodArgumentResolver implements
 			Type targetType) throws IOException, HttpMediaTypeNotSupportedException, HttpMessageNotReadableException {
 
 		MediaType contentType;
+		boolean noContentType = false;
 		try {
 			contentType = inputMessage.getHeaders().getContentType();
 		}
@@ -165,6 +166,7 @@ public abstract class AbstractMessageConverterMethodArgumentResolver implements
 			throw new HttpMediaTypeNotSupportedException(ex.getMessage());
 		}
 		if (contentType == null) {
+			noContentType = true;
 			contentType = MediaType.APPLICATION_OCTET_STREAM;
 		}
 
@@ -220,7 +222,8 @@ public abstract class AbstractMessageConverterMethodArgumentResolver implements
 		}
 
 		if (body == NO_VALUE) {
-			if (!SUPPORTED_METHODS.contains(httpMethod)) {
+			if (!SUPPORTED_METHODS.contains(httpMethod)
+					|| (noContentType && inputMessage.getBody() == null)) {
 				return null;
 			}
 			throw new HttpMediaTypeNotSupportedException(contentType, this.allSupportedMediaTypes);

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/HttpEntityMethodProcessorMockTests.java

@@ -194,6 +194,7 @@ public class HttpEntityMethodProcessorMockTests {
 
 	@Test(expected = HttpMediaTypeNotSupportedException.class)
 	public void resolveArgumentNoContentType() throws Exception {
+		servletRequest.setContent("some content".getBytes(Charset.forName("UTF-8")));
 		processor.resolveArgument(paramHttpEntity, mavContainer, webRequest, null);
 		fail("Expected exception");
 	}

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/RequestResponseBodyMethodProcessorMockTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -212,6 +212,15 @@ public class RequestResponseBodyMethodProcessorMockTests {
 		assertNull(processor.resolveArgument(paramStringNotRequired, mavContainer, webRequest, new ValidatingBinderFactory()));
 	}
 
+	// SPR-13417
+	@Test
+	public void resolveArgumentNotRequiredNoContentNoContentType() throws Exception {
+		servletRequest.setContent(new byte[0]);
+		given(messageConverter.canRead(String.class, MediaType.TEXT_PLAIN)).willReturn(true);
+		given(messageConverter.canRead(String.class, MediaType.APPLICATION_OCTET_STREAM)).willReturn(false);
+		assertNull(processor.resolveArgument(paramStringNotRequired, mavContainer, webRequest, new ValidatingBinderFactory()));
+	}
+
 	@Test
 	public void resolveArgumentNotGetRequests() throws Exception {
 		servletRequest.setMethod("GET");