Refine RequestedContentTypeResolver contract

Consistently return "*/*" if no media types were requested rather than
an empty list. Existing code has to check for both in any case to see
if nothing was requested.

Issue: SPR-16624

spring-webflux/src/main/java/org/springframework/web/reactive/accept/FixedContentTypeResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -23,6 +23,7 @@ import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 
 import org.springframework.http.MediaType;
+import org.springframework.util.Assert;
 import org.springframework.web.server.ServerWebExchange;
 
 /**
@@ -38,7 +39,7 @@ public class FixedContentTypeResolver implements RequestedContentTypeResolver {
 	private static final Log logger = LogFactory.getLog(FixedContentTypeResolver.class);
 
 
-	private final List<MediaType> mediaTypes;
+	private final List<MediaType> contentTypes;
 
 
 	/**
@@ -54,8 +55,9 @@ public class FixedContentTypeResolver implements RequestedContentTypeResolver {
 	 * <p>Consider appending {@link MediaType#ALL} at the end if destinations
 	 * are present which do not support any of the other default media types.
 	 */
-	public FixedContentTypeResolver(List<MediaType> mediaTypes) {
+	public FixedContentTypeResolver(List<MediaType> contentTypes) {
-		this.mediaTypes = Collections.unmodifiableList(mediaTypes);
+		Assert.notNull(contentTypes, "'contentTypes' must not be null");
+		this.contentTypes = Collections.unmodifiableList(contentTypes);
 	}
 
 
@@ -63,16 +65,16 @@ public class FixedContentTypeResolver implements RequestedContentTypeResolver {
 	 * Return the configured list of media types.
 	 */
 	public List<MediaType> getContentTypes() {
-		return this.mediaTypes;
+		return this.contentTypes;
 	}
 
 
 	@Override
 	public List<MediaType> resolveMediaTypes(ServerWebExchange exchange) {
 		if (logger.isDebugEnabled()) {
-			logger.debug("Requested media types: " + this.mediaTypes);
+			logger.debug("Requested media types: " + this.contentTypes);
 		}
-		return this.mediaTypes;
+		return this.contentTypes;
 	}
 
 }

spring-webflux/src/main/java/org/springframework/web/reactive/accept/HeaderContentTypeResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -19,6 +19,7 @@ import java.util.List;
 
 import org.springframework.http.InvalidMediaTypeException;
 import org.springframework.http.MediaType;
+import org.springframework.util.CollectionUtils;
 import org.springframework.web.server.NotAcceptableStatusException;
 import org.springframework.web.server.ServerWebExchange;
 
@@ -35,7 +36,7 @@ public class HeaderContentTypeResolver implements RequestedContentTypeResolver {
 		try {
 			List<MediaType> mediaTypes = exchange.getRequest().getHeaders().getAccept();
 			MediaType.sortBySpecificityAndQuality(mediaTypes);
-			return mediaTypes;
+			return !CollectionUtils.isEmpty(mediaTypes) ? mediaTypes : MEDIA_TYPE_ALL_LIST;
 		}
 		catch (InvalidMediaTypeException ex) {
 			String value = exchange.getRequest().getHeaders().getFirst("Accept");

spring-webflux/src/main/java/org/springframework/web/reactive/accept/ParameterContentTypeResolver.java

@@ -72,7 +72,7 @@ public class ParameterContentTypeResolver implements RequestedContentTypeResolve
 	public List<MediaType> resolveMediaTypes(ServerWebExchange exchange) throws NotAcceptableStatusException {
 		String key = exchange.getRequest().getQueryParams().getFirst(getParameterName());
 		if (!StringUtils.hasText(key)) {
-			return Collections.emptyList();
+			return MEDIA_TYPE_ALL_LIST;
 		}
 		key = formatKey(key);
 		MediaType match = this.mediaTypes.get(key);

spring-webflux/src/main/java/org/springframework/web/reactive/accept/RequestedContentTypeResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -16,6 +16,7 @@
 
 package org.springframework.web.reactive.accept;
 
+import java.util.Collections;
 import java.util.List;
 
 import org.springframework.http.MediaType;
@@ -33,11 +34,20 @@ import org.springframework.web.server.ServerWebExchange;
  */
 public interface RequestedContentTypeResolver {
 
+	/**
+	 * A singleton list with {@link MediaType#ALL} that is returned from
+	 * {@link #resolveMediaTypes} when no specific media types are requested.
+	 * @since 5.0.5
+	 */
+	List<MediaType> MEDIA_TYPE_ALL_LIST = Collections.singletonList(MediaType.ALL);
+
+
 	/**
 	 * Resolve the given request to a list of requested media types. The returned
 	 * list is ordered by specificity first and by quality parameter second.
 	 * @param exchange the current exchange
-	 * @return the requested media types or an empty list
+	 * @return the requested media types, or {@link #MEDIA_TYPE_ALL_LIST} if none
+	 * were requested.
 	 * @throws NotAcceptableStatusException if the requested media type is invalid
 	 */
 	List<MediaType> resolveMediaTypes(ServerWebExchange exchange);

spring-webflux/src/main/java/org/springframework/web/reactive/accept/RequestedContentTypeResolverBuilder.java

@@ -95,13 +95,13 @@ public class RequestedContentTypeResolverBuilder {
 
 		return exchange -> {
 			for (RequestedContentTypeResolver resolver : resolvers) {
-				List<MediaType> type = resolver.resolveMediaTypes(exchange);
+				List<MediaType> mediaTypes = resolver.resolveMediaTypes(exchange);
-				if (type.isEmpty() || (type.size() == 1 && type.contains(MediaType.ALL))) {
+				if (mediaTypes.equals(RequestedContentTypeResolver.MEDIA_TYPE_ALL_LIST)) {
 					continue;
 				}
-				return type;
+				return mediaTypes;
 			}
-			return Collections.emptyList();
+			return RequestedContentTypeResolver.MEDIA_TYPE_ALL_LIST;
 		};
 	}
 

spring-webflux/src/main/java/org/springframework/web/reactive/result/HandlerResultHandlerSupport.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -17,7 +17,6 @@
 package org.springframework.web.reactive.result;
 
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.Comparator;
 import java.util.LinkedHashSet;
 import java.util.List;
@@ -149,8 +148,7 @@ public abstract class HandlerResultHandlerSupport implements Ordered {
 	}
 
 	private List<MediaType> getAcceptableTypes(ServerWebExchange exchange) {
-		List<MediaType> mediaTypes = getContentTypeResolver().resolveMediaTypes(exchange);
+		return getContentTypeResolver().resolveMediaTypes(exchange);
-		return (mediaTypes.isEmpty() ? Collections.singletonList(MediaType.ALL) : mediaTypes);
 	}
 
 	@SuppressWarnings("unchecked")

spring-webflux/src/main/java/org/springframework/web/reactive/result/condition/ProducesRequestCondition.java

@@ -238,11 +238,8 @@ public final class ProducesRequestCondition extends AbstractRequestCondition<Pro
 		}
 	}
 
-	private List<MediaType> getAcceptedMediaTypes(ServerWebExchange exchange)
+	private List<MediaType> getAcceptedMediaTypes(ServerWebExchange exchange) throws NotAcceptableStatusException {
-			throws NotAcceptableStatusException {
+		return this.contentTypeResolver.resolveMediaTypes(exchange);
-
-		List<MediaType> mediaTypes = this.contentTypeResolver.resolveMediaTypes(exchange);
-		return mediaTypes.isEmpty() ? Collections.singletonList(MediaType.ALL) : mediaTypes;
 	}
 
 	private int indexOfEqualMediaType(MediaType mediaType) {

spring-webflux/src/test/java/org/springframework/web/reactive/accept/ParameterContentTypeResolverTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -36,16 +36,16 @@ import static org.junit.Assert.assertEquals;
 public class ParameterContentTypeResolverTests {
 
 	@Test
-	public void noKey() throws Exception {
+	public void noKey() {
 		ParameterContentTypeResolver resolver = new ParameterContentTypeResolver(Collections.emptyMap());
 		ServerWebExchange exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/"));
 		List<MediaType> mediaTypes = resolver.resolveMediaTypes(exchange);
 
-		assertEquals(0, mediaTypes.size());
+		assertEquals(RequestedContentTypeResolver.MEDIA_TYPE_ALL_LIST, mediaTypes);
 	}
 
 	@Test(expected = NotAcceptableStatusException.class)
-	public void noMatchForKey() throws Exception {
+	public void noMatchForKey() {
 		ParameterContentTypeResolver resolver = new ParameterContentTypeResolver(Collections.emptyMap());
 		List<MediaType> mediaTypes = resolver.resolveMediaTypes(createExchange("blah"));
 
@@ -53,7 +53,7 @@ public class ParameterContentTypeResolverTests {
 	}
 
 	@Test
-	public void resolveKeyFromRegistrations() throws Exception {
+	public void resolveKeyFromRegistrations() {
 		ServerWebExchange exchange = createExchange("html");
 
 		Map<String, MediaType> mapping = Collections.emptyMap();
@@ -68,7 +68,7 @@ public class ParameterContentTypeResolverTests {
 	}
 
 	@Test
-	public void resolveKeyThroughMediaTypeFactory() throws Exception {
+	public void resolveKeyThroughMediaTypeFactory() {
 		ServerWebExchange exchange = createExchange("xls");
 		RequestedContentTypeResolver resolver = new ParameterContentTypeResolver(Collections.emptyMap());
 		List<MediaType> mediaTypes = resolver.resolveMediaTypes(exchange);