001/*
002 * Copyright 2002-2020 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.springframework.web.accept;
018
019import java.util.ArrayList;
020import java.util.Arrays;
021import java.util.Collection;
022import java.util.Collections;
023import java.util.HashMap;
024import java.util.LinkedHashSet;
025import java.util.List;
026import java.util.Map;
027import java.util.Set;
028import java.util.function.Function;
029
030import org.springframework.http.MediaType;
031import org.springframework.lang.Nullable;
032import org.springframework.util.Assert;
033import org.springframework.util.CollectionUtils;
034import org.springframework.web.HttpMediaTypeNotAcceptableException;
035import org.springframework.web.context.request.NativeWebRequest;
036
037/**
038 * Central class to determine requested {@linkplain MediaType media types}
039 * for a request. This is done by delegating to a list of configured
040 * {@code ContentNegotiationStrategy} instances.
041 *
042 * <p>Also provides methods to look up file extensions for a media type.
043 * This is done by delegating to the list of configured
044 * {@code MediaTypeFileExtensionResolver} instances.
045 *
046 * @author Rossen Stoyanchev
047 * @author Juergen Hoeller
048 * @since 3.2
049 */
050public class ContentNegotiationManager implements ContentNegotiationStrategy, MediaTypeFileExtensionResolver {
051
052        private final List<ContentNegotiationStrategy> strategies = new ArrayList<>();
053
054        private final Set<MediaTypeFileExtensionResolver> resolvers = new LinkedHashSet<>();
055
056
057        /**
058         * Create an instance with the given list of
059         * {@code ContentNegotiationStrategy} strategies each of which may also be
060         * an instance of {@code MediaTypeFileExtensionResolver}.
061         * @param strategies the strategies to use
062         */
063        public ContentNegotiationManager(ContentNegotiationStrategy... strategies) {
064                this(Arrays.asList(strategies));
065        }
066
067        /**
068         * A collection-based alternative to
069         * {@link #ContentNegotiationManager(ContentNegotiationStrategy...)}.
070         * @param strategies the strategies to use
071         * @since 3.2.2
072         */
073        public ContentNegotiationManager(Collection<ContentNegotiationStrategy> strategies) {
074                Assert.notEmpty(strategies, "At least one ContentNegotiationStrategy is expected");
075                this.strategies.addAll(strategies);
076                for (ContentNegotiationStrategy strategy : this.strategies) {
077                        if (strategy instanceof MediaTypeFileExtensionResolver) {
078                                this.resolvers.add((MediaTypeFileExtensionResolver) strategy);
079                        }
080                }
081        }
082
083        /**
084         * Create a default instance with a {@link HeaderContentNegotiationStrategy}.
085         */
086        public ContentNegotiationManager() {
087                this(new HeaderContentNegotiationStrategy());
088        }
089
090
091        /**
092         * Return the configured content negotiation strategies.
093         * @since 3.2.16
094         */
095        public List<ContentNegotiationStrategy> getStrategies() {
096                return this.strategies;
097        }
098
099        /**
100         * Find a {@code ContentNegotiationStrategy} of the given type.
101         * @param strategyType the strategy type
102         * @return the first matching strategy, or {@code null} if none
103         * @since 4.3
104         */
105        @SuppressWarnings("unchecked")
106        @Nullable
107        public <T extends ContentNegotiationStrategy> T getStrategy(Class<T> strategyType) {
108                for (ContentNegotiationStrategy strategy : getStrategies()) {
109                        if (strategyType.isInstance(strategy)) {
110                                return (T) strategy;
111                        }
112                }
113                return null;
114        }
115
116        /**
117         * Register more {@code MediaTypeFileExtensionResolver} instances in addition
118         * to those detected at construction.
119         * @param resolvers the resolvers to add
120         */
121        public void addFileExtensionResolvers(MediaTypeFileExtensionResolver... resolvers) {
122                Collections.addAll(this.resolvers, resolvers);
123        }
124
125        @Override
126        public List<MediaType> resolveMediaTypes(NativeWebRequest request) throws HttpMediaTypeNotAcceptableException {
127                for (ContentNegotiationStrategy strategy : this.strategies) {
128                        List<MediaType> mediaTypes = strategy.resolveMediaTypes(request);
129                        if (mediaTypes.equals(MEDIA_TYPE_ALL_LIST)) {
130                                continue;
131                        }
132                        return mediaTypes;
133                }
134                return MEDIA_TYPE_ALL_LIST;
135        }
136
137        @Override
138        public List<String> resolveFileExtensions(MediaType mediaType) {
139                return doResolveExtensions(resolver -> resolver.resolveFileExtensions(mediaType));
140        }
141
142        /**
143         * {@inheritDoc}
144         * <p>At startup this method returns extensions explicitly registered with
145         * either {@link PathExtensionContentNegotiationStrategy} or
146         * {@link ParameterContentNegotiationStrategy}. At runtime if there is a
147         * "path extension" strategy and its
148         * {@link PathExtensionContentNegotiationStrategy#setUseRegisteredExtensionsOnly(boolean)
149         * useRegisteredExtensionsOnly} property is set to "false", the list of extensions may
150         * increase as file extensions are resolved via
151         * {@link org.springframework.http.MediaTypeFactory} and cached.
152         */
153        @Override
154        public List<String> getAllFileExtensions() {
155                return doResolveExtensions(MediaTypeFileExtensionResolver::getAllFileExtensions);
156        }
157
158        private List<String> doResolveExtensions(Function<MediaTypeFileExtensionResolver, List<String>> extractor) {
159                List<String> result = null;
160                for (MediaTypeFileExtensionResolver resolver : this.resolvers) {
161                        List<String> extensions = extractor.apply(resolver);
162                        if (CollectionUtils.isEmpty(extensions)) {
163                                continue;
164                        }
165                        result = (result != null ? result : new ArrayList<>(4));
166                        for (String extension : extensions) {
167                                if (!result.contains(extension)) {
168                                        result.add(extension);
169                                }
170                        }
171                }
172                return (result != null ? result : Collections.emptyList());
173        }
174
175        /**
176         * Return all registered lookup key to media type mappings by iterating
177         * {@link MediaTypeFileExtensionResolver}s.
178         * @since 5.2.4
179         */
180        public Map<String, MediaType> getMediaTypeMappings() {
181                Map<String, MediaType> result = null;
182                for (MediaTypeFileExtensionResolver resolver : this.resolvers) {
183                        if (resolver instanceof MappingMediaTypeFileExtensionResolver) {
184                                Map<String, MediaType> map = ((MappingMediaTypeFileExtensionResolver) resolver).getMediaTypes();
185                                if (CollectionUtils.isEmpty(map)) {
186                                        continue;
187                                }
188                                result = (result != null ? result : new HashMap<>(4));
189                                result.putAll(map);
190                        }
191                }
192                return (result != null ? result : Collections.emptyMap());
193        }
194
195}