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/*
 * Copyright 2002-2017 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
 *
 *      http://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.Collections;
import java.util.List;
import java.util.Map;

import org.springframework.http.MediaType;
import org.springframework.util.StringUtils;
import org.springframework.web.HttpMediaTypeNotAcceptableException;
import org.springframework.web.context.request.NativeWebRequest;

/**
 * Base class for {@code ContentNegotiationStrategy} implementations with the
 * steps to resolve a request to media types.
 *
 * 

First a key (e.g. "json", "pdf") must be extracted from the request (e.g. * file extension, query param). The key must then be resolved to media type(s) * through the base class {@link MappingMediaTypeFileExtensionResolver} which * stores such mappings. * *

The method {@link #handleNoMatch} allow sub-classes to plug in additional * ways of looking up media types (e.g. through the Java Activation framework, * or {@link javax.servlet.ServletContext#getMimeType}. Media types resolved * via base classes are then added to the base class * {@link MappingMediaTypeFileExtensionResolver}, i.e. cached for new lookups. * * @author Rossen Stoyanchev * @since 3.2 */ public abstract class AbstractMappingContentNegotiationStrategy extends MappingMediaTypeFileExtensionResolver implements ContentNegotiationStrategy { /** * Create an instance with the given map of file extensions and media types. */ public AbstractMappingContentNegotiationStrategy(Map mediaTypes) { super(mediaTypes); } @Override public List resolveMediaTypes(NativeWebRequest webRequest) throws HttpMediaTypeNotAcceptableException { return resolveMediaTypeKey(webRequest, getMediaTypeKey(webRequest)); } /** * An alternative to {@link #resolveMediaTypes(NativeWebRequest)} that accepts * an already extracted key. * @since 3.2.16 */ public List resolveMediaTypeKey(NativeWebRequest webRequest, String key) throws HttpMediaTypeNotAcceptableException { if (StringUtils.hasText(key)) { MediaType mediaType = lookupMediaType(key); if (mediaType != null) { handleMatch(key, mediaType); return Collections.singletonList(mediaType); } mediaType = handleNoMatch(webRequest, key); if (mediaType != null) { addMapping(key, mediaType); return Collections.singletonList(mediaType); } } return Collections.emptyList(); } /** * Extract a key from the request to use to look up media types. * @return the lookup key, or {@code null} if none */ protected abstract String getMediaTypeKey(NativeWebRequest request); /** * Override to provide handling when a key is successfully resolved via * {@link #lookupMediaType}. */ protected void handleMatch(String key, MediaType mediaType) { } /** * Override to provide handling when a key is not resolved via. * {@link #lookupMediaType}. Sub-classes can take further steps to * determine the media type(s). If a MediaType is returned from * this method it will be added to the cache in the base class. */ protected MediaType handleNoMatch(NativeWebRequest request, String key) throws HttpMediaTypeNotAcceptableException { return null; } }





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