Improve default content type selection

Previously ContentNegotiationManager continued with the next
ContentNegotiationStrategy only if the current one returned an empty
list. Now it also does that if the current ContentNegotiationStrategy
returns "*/*". Since the absence of an Accept header and "*/*" have
the same meaning, this allows a default content type to be used in
either case.

Issue: SPR-10513

Author: rstoyanchev

spring-web/src/main/java/org/springframework/web/accept/ContentNegotiationManager.java

@@ -50,6 +50,8 @@
  */
 public class ContentNegotiationManager implements ContentNegotiationStrategy, MediaTypeFileExtensionResolver {
 
+	private static final List<MediaType> MEDIA_TYPE_ALL = Arrays.asList(MediaType.ALL);
+
 	private final List<ContentNegotiationStrategy> contentNegotiationStrategies =
 			new ArrayList<ContentNegotiationStrategy>();
 
@@ -119,9 +121,10 @@ public void addFileExtensionResolvers(MediaTypeFileExtensionResolver... resolver
 	public List<MediaType> resolveMediaTypes(NativeWebRequest webRequest) throws HttpMediaTypeNotAcceptableException {
 		for (ContentNegotiationStrategy strategy : this.contentNegotiationStrategies) {
 			List<MediaType> mediaTypes = strategy.resolveMediaTypes(webRequest);
-			if (!mediaTypes.isEmpty()) {
-				return mediaTypes;
+			if (mediaTypes.isEmpty() || mediaTypes.equals(MEDIA_TYPE_ALL)) {
+				continue;
 			}
+			return mediaTypes;
 		}
 		return Collections.emptyList();
 	}

spring-web/src/test/java/org/springframework/web/accept/ContentNegotiationManagerFactoryBeanTests.java

@@ -122,6 +122,12 @@ public void setDefaultContentType() throws Exception {
 		ContentNegotiationManager manager = this.factoryBean.getObject();
 
 		assertEquals(Arrays.asList(MediaType.APPLICATION_JSON), manager.resolveMediaTypes(this.webRequest));
+
+		// SPR-10513
+
+		this.servletRequest.addHeader("Accept", MediaType.ALL_VALUE);
+
+		assertEquals(Arrays.asList(MediaType.APPLICATION_JSON), manager.resolveMediaTypes(this.webRequest));
 	}
 
 }