org.springframework/spring-webmvc/5.3.3 : org/springframework/web/servlet/view/ContentNegotiatingViewResolver.java

ContentNegotiatingViewResolver
https://github.com/spring-projects/spring-framework: Spring Web MVC (Spring IO)
Apache License, Version 2.0
Juergen Hoeller
/*
 * 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.servlet.view;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Set;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.beans.factory.BeanFactoryUtils;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.core.Ordered;
import org.springframework.core.annotation.AnnotationAwareOrderComparator;
import org.springframework.http.MediaType;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.CollectionUtils;
import org.springframework.util.StringUtils;
import org.springframework.web.HttpMediaTypeNotAcceptableException;
import org.springframework.web.accept.ContentNegotiationManager;
import org.springframework.web.accept.ContentNegotiationManagerFactoryBean;
import org.springframework.web.context.request.RequestAttributes;
import org.springframework.web.context.request.RequestContextHolder;
import org.springframework.web.context.request.ServletRequestAttributes;
import org.springframework.web.context.request.ServletWebRequest;
import org.springframework.web.context.support.WebApplicationObjectSupport;
import org.springframework.web.servlet.HandlerMapping;
import org.springframework.web.servlet.SmartView;
import org.springframework.web.servlet.View;
import org.springframework.web.servlet.ViewResolver;

Implementation of ViewResolver that resolves a view based on the request file name or Accept header. The ContentNegotiatingViewResolver does not resolve views itself, but delegates to other ViewResolvers. By default, these other view resolvers are picked up automatically from the application context, though they can also be set explicitly by using the viewResolvers property. Note that in order for this view resolver to work properly, the order property needs to be set to a higher precedence than the others (the default is Ordered.HIGHEST_PRECEDENCE). 
This view resolver uses the requested media type to select a suitable View for a request. The requested media type is determined through the configured ContentNegotiationManager. Once the requested media type has been determined, this resolver queries each delegate view resolver for a View and determines if the requested media type is compatible with the view's content type). The most compatible view is returned. 
Additionally, this view resolver exposes the defaultViews property, allowing you to override the views provided by the view resolvers. Note that these default views are offered as candidates, and still need have the content type requested (via file extension, parameter, or Accept header, described above). 
For example, if the request path is /view.html, this view resolver will look for a view that has the text/html content type (based on the html file extension). A request for /view with a text/html request Accept header has the same result. 
Author: Arjen Poutsma, Juergen Hoeller, Rossen Stoyanchev
See Also: ViewResolver
InternalResourceViewResolver
BeanNameViewResolver
Since: 3.0/**
 * Implementation of {@link ViewResolver} that resolves a view based on the request file name
 * or {@code Accept} header.
 *
 * <p>The {@code ContentNegotiatingViewResolver} does not resolve views itself, but delegates to
 * other {@link ViewResolver ViewResolvers}. By default, these other view resolvers are picked up automatically
 * from the application context, though they can also be set explicitly by using the
 * {@link #setViewResolvers viewResolvers} property. <strong>Note</strong> that in order for this
 * view resolver to work properly, the {@link #setOrder order} property needs to be set to a higher
 * precedence than the others (the default is {@link Ordered#HIGHEST_PRECEDENCE}).
 *
 * <p>This view resolver uses the requested {@linkplain MediaType media type} to select a suitable
 * {@link View} for a request. The requested media type is determined through the configured
 * {@link ContentNegotiationManager}. Once the requested media type has been determined, this resolver
 * queries each delegate view resolver for a {@link View} and determines if the requested media type
 * is {@linkplain MediaType#includes(MediaType) compatible} with the view's
 * {@linkplain View#getContentType() content type}). The most compatible view is returned.
 *
 * <p>Additionally, this view resolver exposes the {@link #setDefaultViews(List) defaultViews} property,
 * allowing you to override the views provided by the view resolvers. Note that these default views are
 * offered as candidates, and still need have the content type requested (via file extension, parameter,
 * or {@code Accept} header, described above).
 *
 * <p>For example, if the request path is {@code /view.html}, this view resolver will look for a view
 * that has the {@code text/html} content type (based on the {@code html} file extension). A request
 * for {@code /view} with a {@code text/html} request {@code Accept} header has the same result.
 *
 * @author Arjen Poutsma
 * @author Juergen Hoeller
 * @author Rossen Stoyanchev
 * @since 3.0
 * @see ViewResolver
 * @see InternalResourceViewResolver
 * @see BeanNameViewResolver
 */
public class ContentNegotiatingViewResolver extends WebApplicationObjectSupport
		implements ViewResolver, Ordered, InitializingBean {

	@Nullable
	private ContentNegotiationManager contentNegotiationManager;

	private final ContentNegotiationManagerFactoryBean cnmFactoryBean = new ContentNegotiationManagerFactoryBean();

	private boolean useNotAcceptableStatusCode = false;

	@Nullable
	private List<View> defaultViews;

	@Nullable
	private List<ViewResolver> viewResolvers;

	private int order = Ordered.HIGHEST_PRECEDENCE;


	Set the ContentNegotiationManager to use to determine requested media types. If not set, ContentNegotiationManager's default constructor will be used, applying a HeaderContentNegotiationStrategy. 
See Also: ContentNegotiationManager()/**
	 * Set the {@link ContentNegotiationManager} to use to determine requested media types.
	 * <p>If not set, ContentNegotiationManager's default constructor will be used,
	 * applying a {@link org.springframework.web.accept.HeaderContentNegotiationStrategy}.
	 * @see ContentNegotiationManager#ContentNegotiationManager()
	 */
	public void setContentNegotiationManager(@Nullable ContentNegotiationManager contentNegotiationManager) {
		this.contentNegotiationManager = contentNegotiationManager;
	}

	Return the ContentNegotiationManager to use to determine requested media types. 
Since: 4.1.9/**
	 * Return the {@link ContentNegotiationManager} to use to determine requested media types.
	 * @since 4.1.9
	 */
	@Nullable
	public ContentNegotiationManager getContentNegotiationManager() {
		return this.contentNegotiationManager;
	}

	Indicate whether a 406 Not Acceptable status code should be returned if no suitable view can be found. Default is false, meaning that this view resolver returns null for resolveViewName(String, Locale) when an acceptable view cannot be found. This will allow for view resolvers chaining. When this property is set to true, resolveViewName(String, Locale) will respond with a view that sets the response status to 406 Not Acceptable instead. /**
	 * Indicate whether a {@link HttpServletResponse#SC_NOT_ACCEPTABLE 406 Not Acceptable}
	 * status code should be returned if no suitable view can be found.
	 * <p>Default is {@code false}, meaning that this view resolver returns {@code null} for
	 * {@link #resolveViewName(String, Locale)} when an acceptable view cannot be found.
	 * This will allow for view resolvers chaining. When this property is set to {@code true},
	 * {@link #resolveViewName(String, Locale)} will respond with a view that sets the
	 * response status to {@code 406 Not Acceptable} instead.
	 */
	public void setUseNotAcceptableStatusCode(boolean useNotAcceptableStatusCode) {
		this.useNotAcceptableStatusCode = useNotAcceptableStatusCode;
	}

	Whether to return HTTP Status 406 if no suitable is found.
/**
	 * Whether to return HTTP Status 406 if no suitable is found.
	 */
	public boolean isUseNotAcceptableStatusCode() {
		return this.useNotAcceptableStatusCode;
	}

	Set the default views to use when a more specific view can not be obtained from the ViewResolver chain. /**
	 * Set the default views to use when a more specific view can not be obtained
	 * from the {@link ViewResolver} chain.
	 */
	public void setDefaultViews(List<View> defaultViews) {
		this.defaultViews = defaultViews;
	}

	public List<View> getDefaultViews() {
		return (this.defaultViews != null ? Collections.unmodifiableList(this.defaultViews) :
				Collections.emptyList());
	}

	Sets the view resolvers to be wrapped by this view resolver.
If this property is not set, view resolvers will be detected automatically.
/**
	 * Sets the view resolvers to be wrapped by this view resolver.
	 * <p>If this property is not set, view resolvers will be detected automatically.
	 */
	public void setViewResolvers(List<ViewResolver> viewResolvers) {
		this.viewResolvers = viewResolvers;
	}

	public List<ViewResolver> getViewResolvers() {
		return (this.viewResolvers != null ? Collections.unmodifiableList(this.viewResolvers) :
				Collections.emptyList());
	}

	public void setOrder(int order) {
		this.order = order;
	}

	@Override
	public int getOrder() {
		return this.order;
	}


	@Override
	protected void initServletContext(ServletContext servletContext) {
		Collection<ViewResolver> matchingBeans =
				BeanFactoryUtils.beansOfTypeIncludingAncestors(obtainApplicationContext(), ViewResolver.class).values();
		if (this.viewResolvers == null) {
			this.viewResolvers = new ArrayList<>(matchingBeans.size());
			for (ViewResolver viewResolver : matchingBeans) {
				if (this != viewResolver) {
					this.viewResolvers.add(viewResolver);
				}
			}
		}
		else {
			for (int i = 0; i < this.viewResolvers.size(); i++) {
				ViewResolver vr = this.viewResolvers.get(i);
				if (matchingBeans.contains(vr)) {
					continue;
				}
				String name = vr.getClass().getName() + i;
				obtainApplicationContext().getAutowireCapableBeanFactory().initializeBean(vr, name);
			}

		}
		AnnotationAwareOrderComparator.sort(this.viewResolvers);
		this.cnmFactoryBean.setServletContext(servletContext);
	}

	@Override
	public void afterPropertiesSet() {
		if (this.contentNegotiationManager == null) {
			this.contentNegotiationManager = this.cnmFactoryBean.build();
		}
		if (this.viewResolvers == null || this.viewResolvers.isEmpty()) {
			logger.warn("No ViewResolvers configured");
		}
	}


	@Override
	@Nullable
	public View resolveViewName(String viewName, Locale locale) throws Exception {
		RequestAttributes attrs = RequestContextHolder.getRequestAttributes();
		Assert.state(attrs instanceof ServletRequestAttributes, "No current ServletRequestAttributes");
		List<MediaType> requestedMediaTypes = getMediaTypes(((ServletRequestAttributes) attrs).getRequest());
		if (requestedMediaTypes != null) {
			List<View> candidateViews = getCandidateViews(viewName, locale, requestedMediaTypes);
			View bestView = getBestView(candidateViews, requestedMediaTypes, attrs);
			if (bestView != null) {
				return bestView;
			}
		}

		String mediaTypeInfo = logger.isDebugEnabled() && requestedMediaTypes != null ?
				" given " + requestedMediaTypes.toString() : "";

		if (this.useNotAcceptableStatusCode) {
			if (logger.isDebugEnabled()) {
				logger.debug("Using 406 NOT_ACCEPTABLE" + mediaTypeInfo);
			}
			return NOT_ACCEPTABLE_VIEW;
		}
		else {
			logger.debug("View remains unresolved" + mediaTypeInfo);
			return null;
		}
	}

	Determines the list of MediaType for the given HttpServletRequest. 
Params: request – the current servlet request
Returns: the list of media types requested, if any/**
	 * Determines the list of {@link MediaType} for the given {@link HttpServletRequest}.
	 * @param request the current servlet request
	 * @return the list of media types requested, if any
	 */
	@Nullable
	protected List<MediaType> getMediaTypes(HttpServletRequest request) {
		Assert.state(this.contentNegotiationManager != null, "No ContentNegotiationManager set");
		try {
			ServletWebRequest webRequest = new ServletWebRequest(request);
			List<MediaType> acceptableMediaTypes = this.contentNegotiationManager.resolveMediaTypes(webRequest);
			List<MediaType> producibleMediaTypes = getProducibleMediaTypes(request);
			Set<MediaType> compatibleMediaTypes = new LinkedHashSet<>();
			for (MediaType acceptable : acceptableMediaTypes) {
				for (MediaType producible : producibleMediaTypes) {
					if (acceptable.isCompatibleWith(producible)) {
						compatibleMediaTypes.add(getMostSpecificMediaType(acceptable, producible));
					}
				}
			}
			List<MediaType> selectedMediaTypes = new ArrayList<>(compatibleMediaTypes);
			MediaType.sortBySpecificityAndQuality(selectedMediaTypes);
			return selectedMediaTypes;
		}
		catch (HttpMediaTypeNotAcceptableException ex) {
			if (logger.isDebugEnabled()) {
				logger.debug(ex.getMessage());
			}
			return null;
		}
	}

	@SuppressWarnings("unchecked")
	private List<MediaType> getProducibleMediaTypes(HttpServletRequest request) {
		Set<MediaType> mediaTypes = (Set<MediaType>)
				request.getAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);
		if (!CollectionUtils.isEmpty(mediaTypes)) {
			return new ArrayList<>(mediaTypes);
		}
		else {
			return Collections.singletonList(MediaType.ALL);
		}
	}

	Return the more specific of the acceptable and the producible media types
with the q-value of the former.
/**
	 * Return the more specific of the acceptable and the producible media types
	 * with the q-value of the former.
	 */
	private MediaType getMostSpecificMediaType(MediaType acceptType, MediaType produceType) {
		produceType = produceType.copyQualityValue(acceptType);
		return (MediaType.SPECIFICITY_COMPARATOR.compare(acceptType, produceType) < 0 ? acceptType : produceType);
	}

	private List<View> getCandidateViews(String viewName, Locale locale, List<MediaType> requestedMediaTypes)
			throws Exception {

		List<View> candidateViews = new ArrayList<>();
		if (this.viewResolvers != null) {
			Assert.state(this.contentNegotiationManager != null, "No ContentNegotiationManager set");
			for (ViewResolver viewResolver : this.viewResolvers) {
				View view = viewResolver.resolveViewName(viewName, locale);
				if (view != null) {
					candidateViews.add(view);
				}
				for (MediaType requestedMediaType : requestedMediaTypes) {
					List<String> extensions = this.contentNegotiationManager.resolveFileExtensions(requestedMediaType);
					for (String extension : extensions) {
						String viewNameWithExtension = viewName + '.' + extension;
						view = viewResolver.resolveViewName(viewNameWithExtension, locale);
						if (view != null) {
							candidateViews.add(view);
						}
					}
				}
			}
		}
		if (!CollectionUtils.isEmpty(this.defaultViews)) {
			candidateViews.addAll(this.defaultViews);
		}
		return candidateViews;
	}

	@Nullable
	private View getBestView(List<View> candidateViews, List<MediaType> requestedMediaTypes, RequestAttributes attrs) {
		for (View candidateView : candidateViews) {
			if (candidateView instanceof SmartView) {
				SmartView smartView = (SmartView) candidateView;
				if (smartView.isRedirectView()) {
					return candidateView;
				}
			}
		}
		for (MediaType mediaType : requestedMediaTypes) {
			for (View candidateView : candidateViews) {
				if (StringUtils.hasText(candidateView.getContentType())) {
					MediaType candidateContentType = MediaType.parseMediaType(candidateView.getContentType());
					if (mediaType.isCompatibleWith(candidateContentType)) {
						if (logger.isDebugEnabled()) {
							logger.debug("Selected '" + mediaType + "' given " + requestedMediaTypes);
						}
						attrs.setAttribute(View.SELECTED_CONTENT_TYPE, mediaType, RequestAttributes.SCOPE_REQUEST);
						return candidateView;
					}
				}
			}
		}
		return null;
	}


	private static final View NOT_ACCEPTABLE_VIEW = new View() {

		@Override
		@Nullable
		public String getContentType() {
			return null;
		}

		@Override
		public void render(@Nullable Map<String, ?> model, HttpServletRequest request, HttpServletResponse response) {
			response.setStatus(HttpServletResponse.SC_NOT_ACCEPTABLE);
		}
	};

}
Author:	Arjen Poutsma, Juergen Hoeller, Rossen Stoyanchev
See Also:	ViewResolver InternalResourceViewResolver BeanNameViewResolver
Since:	3.0
Params:	request – the current servlet request
Returns:	the list of media types requested, if any
/

org.springframework/ spring-webmvc/ 5.3.3/ org/springframework/web/servlet/view/ContentNegotiatingViewResolver.java
