spring AbstractMappingContentNegotiationStrategy 源码

spring AbstractMappingContentNegotiationStrategy 代码

文件路径：/spring-web/src/main/java/org/springframework/web/accept/AbstractMappingContentNegotiationStrategy.java

/*
 * 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.Collections;
import java.util.List;
import java.util.Map;
import java.util.Optional;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.http.MediaType;
import org.springframework.http.MediaTypeFactory;
import org.springframework.lang.Nullable;
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 subclasses to plug in additional
 * ways of looking up media types (e.g. through the Java Activation framework,
 * or {@link jakarta.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 {

	protected final Log logger = LogFactory.getLog(getClass());

	private boolean useRegisteredExtensionsOnly = false;

	private boolean ignoreUnknownExtensions = false;


	/**
	 * Create an instance with the given map of file extensions and media types.
	 */
	public AbstractMappingContentNegotiationStrategy(@Nullable Map<String, MediaType> mediaTypes) {
		super(mediaTypes);
	}


	/**
	 * Whether to only use the registered mappings to look up file extensions,
	 * or also to use dynamic resolution (e.g. via {@link MediaTypeFactory}.
	 * <p>By default this is set to {@code false}.
	 */
	public void setUseRegisteredExtensionsOnly(boolean useRegisteredExtensionsOnly) {
		this.useRegisteredExtensionsOnly = useRegisteredExtensionsOnly;
	}

	public boolean isUseRegisteredExtensionsOnly() {
		return this.useRegisteredExtensionsOnly;
	}

	/**
	 * Whether to ignore requests with unknown file extension. Setting this to
	 * {@code false} results in {@code HttpMediaTypeNotAcceptableException}.
	 * <p>By default this is set to {@literal false} but is overridden in
	 * {@link PathExtensionContentNegotiationStrategy} to {@literal true}.
	 */
	public void setIgnoreUnknownExtensions(boolean ignoreUnknownExtensions) {
		this.ignoreUnknownExtensions = ignoreUnknownExtensions;
	}

	public boolean isIgnoreUnknownExtensions() {
		return this.ignoreUnknownExtensions;
	}


	@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, @Nullable 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 MEDIA_TYPE_ALL_LIST;
	}


	/**
	 * Extract a key from the request to use to look up media types.
	 * @return the lookup key, or {@code null} if none
	 */
	@Nullable
	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}. Subclasses 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.
	 */
	@Nullable
	protected MediaType handleNoMatch(NativeWebRequest request, String key)
			throws HttpMediaTypeNotAcceptableException {

		if (!isUseRegisteredExtensionsOnly()) {
			Optional<MediaType> mediaType = MediaTypeFactory.getMediaType("file." + key);
			if (mediaType.isPresent()) {
				return mediaType.get();
			}
		}
		if (isIgnoreUnknownExtensions()) {
			return null;
		}
		throw new HttpMediaTypeNotAcceptableException(getAllMediaTypes());
	}

}

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