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/*
* Copyright 2002-2016 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.
*
* <p>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.
*
* <p>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<String, MediaType> mediaTypes) {
super(mediaTypes);
}
@Override
public List<MediaType> 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<MediaType> 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}.
*/
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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