org.springframework.web.accept.ContentNegotiationManager.java Source code

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Here is the source code for org.springframework.web.accept.ContentNegotiationManager.java

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/*
 * 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.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.accept;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;

import org.springframework.http.MediaType;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.web.HttpMediaTypeNotAcceptableException;
import org.springframework.web.context.request.NativeWebRequest;

/**
 * Central class to determine requested {@linkplain MediaType media types}
 * for a request. This is done by delegating to a list of configured
 * {@code ContentNegotiationStrategy} instances.
 *
 * <p>Also provides methods to look up file extensions for a media type.
 * This is done by delegating to the list of configured
 * {@code MediaTypeFileExtensionResolver} instances.
 *
 * @author Rossen Stoyanchev
 * @author Juergen Hoeller
 * @since 3.2
 */
public class ContentNegotiationManager implements ContentNegotiationStrategy, MediaTypeFileExtensionResolver {

    private final List<ContentNegotiationStrategy> strategies = new ArrayList<>();

    private final Set<MediaTypeFileExtensionResolver> resolvers = new LinkedHashSet<>();

    /**
     * Create an instance with the given list of
     * {@code ContentNegotiationStrategy} strategies each of which may also be
     * an instance of {@code MediaTypeFileExtensionResolver}.
     * @param strategies the strategies to use
     */
    public ContentNegotiationManager(ContentNegotiationStrategy... strategies) {
        this(Arrays.asList(strategies));
    }

    /**
     * A collection-based alternative to
     * {@link #ContentNegotiationManager(ContentNegotiationStrategy...)}.
     * @param strategies the strategies to use
     * @since 3.2.2
     */
    public ContentNegotiationManager(Collection<ContentNegotiationStrategy> strategies) {
        Assert.notEmpty(strategies, "At least one ContentNegotiationStrategy is expected");
        this.strategies.addAll(strategies);
        for (ContentNegotiationStrategy strategy : this.strategies) {
            if (strategy instanceof MediaTypeFileExtensionResolver) {
                this.resolvers.add((MediaTypeFileExtensionResolver) strategy);
            }
        }
    }

    /**
     * Create a default instance with a {@link HeaderContentNegotiationStrategy}.
     */
    public ContentNegotiationManager() {
        this(new HeaderContentNegotiationStrategy());
    }

    /**
     * Return the configured content negotiation strategies.
     * @since 3.2.16
     */
    public List<ContentNegotiationStrategy> getStrategies() {
        return this.strategies;
    }

    /**
     * Find a {@code ContentNegotiationStrategy} of the given type.
     * @param strategyType the strategy type
     * @return the first matching strategy, or {@code null} if none
     * @since 4.3
     */
    @SuppressWarnings("unchecked")
    @Nullable
    public <T extends ContentNegotiationStrategy> T getStrategy(Class<T> strategyType) {
        for (ContentNegotiationStrategy strategy : getStrategies()) {
            if (strategyType.isInstance(strategy)) {
                return (T) strategy;
            }
        }
        return null;
    }

    /**
     * Register more {@code MediaTypeFileExtensionResolver} instances in addition
     * to those detected at construction.
     * @param resolvers the resolvers to add
     */
    public void addFileExtensionResolvers(MediaTypeFileExtensionResolver... resolvers) {
        Collections.addAll(this.resolvers, resolvers);
    }

    @Override
    public List<MediaType> resolveMediaTypes(NativeWebRequest request) throws HttpMediaTypeNotAcceptableException {
        for (ContentNegotiationStrategy strategy : this.strategies) {
            List<MediaType> mediaTypes = strategy.resolveMediaTypes(request);
            if (mediaTypes.equals(MEDIA_TYPE_ALL_LIST)) {
                continue;
            }
            return mediaTypes;
        }
        return MEDIA_TYPE_ALL_LIST;
    }

    @Override
    public List<String> resolveFileExtensions(MediaType mediaType) {
        Set<String> result = new LinkedHashSet<>();
        for (MediaTypeFileExtensionResolver resolver : this.resolvers) {
            result.addAll(resolver.resolveFileExtensions(mediaType));
        }
        return new ArrayList<>(result);
    }

    /**
     * {@inheritDoc}
     * <p>At startup this method returns extensions explicitly registered with
     * either {@link PathExtensionContentNegotiationStrategy} or
     * {@link ParameterContentNegotiationStrategy}. At runtime if there is a
     * "path extension" strategy and its
     * {@link PathExtensionContentNegotiationStrategy#setUseRegisteredExtensionsOnly(boolean)
     * useRegisteredExtensionsOnly} property is set to "false", the list of extensions may
     * increase as file extensions are resolved via
     * {@link org.springframework.http.MediaTypeFactory} and cached.
     */
    @Override
    public List<String> getAllFileExtensions() {
        Set<String> result = new LinkedHashSet<>();
        for (MediaTypeFileExtensionResolver resolver : this.resolvers) {
            result.addAll(resolver.getAllFileExtensions());
        }
        return new ArrayList<>(result);
    }

}