SpringMVC源码总结（十二）ViewResolver介绍

String getContentType();/*** Render the view given the specified model.* <p>The first step will be preparing the request: In the JSP case,* this would mean setting model objects as request attributes.* The second step will be the actual rendering of the view,* for example including the JSP via a RequestDispatcher.* @param model Map with name Strings as keys and corresponding model* objects as values (Map can also be {@code null} in case of empty model)* @param request current HTTP request* @param response HTTP response we are building* @throws Exception if rendering failed*/
//上面说的很清楚，对于jsp来说，第一步就是将model作为request的attributes；第二步才开始渲染viewvoid render(Map<String, ?> model, HttpServletRequest request, HttpServletResponse response) throws Exception;

View resolveViewName(String viewName, Locale locale) throws Exception;

try {// Actually invoke the handler.mv = ha.handle(processedRequest, response, mappedHandler.getHandler());}finally {if (asyncManager.isConcurrentHandlingStarted()) {return;}}applyDefaultViewName(request, mv);mappedHandler.applyPostHandle(processedRequest, response, mv);}catch (Exception ex) {dispatchException = ex;}
//这里是我们的关注重点，就是进行视图渲染的过程processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);}catch (Exception ex) {triggerAfterCompletion(processedRequest, response, mappedHandler, ex);}catch (Error err) {triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err);}

private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {boolean errorView = false;if (exception != null) {if (exception instanceof ModelAndViewDefiningException) {logger.debug("ModelAndViewDefiningException encountered", exception);mv = ((ModelAndViewDefiningException) exception).getModelAndView();}else {Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);mv = processHandlerException(request, response, handler, exception);errorView = (mv != null);}}// Did the handler return a view to render?
//这里是我们关注的重点if (mv != null && !mv.wasCleared()) {render(mv, request, response);if (errorView) {WebUtils.clearErrorRequestAttributes(request);}}else {if (logger.isDebugEnabled()) {logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +"': assuming HandlerAdapter completed request handling");}}if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {// Concurrent handling started during a forwardreturn;}if (mappedHandler != null) {mappedHandler.triggerAfterCompletion(request, response, null);}}

protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {// Determine locale for request and apply it to the response.Locale locale = this.localeResolver.resolveLocale(request);response.setLocale(locale);View view;if (mv.isReference()) {// We need to resolve the view name.view = resolveViewName(mv.getViewName(), mv.getModelInternal(), locale, request);if (view == null) {throw new ServletException("Could not resolve view with name '" + mv.getViewName() +"' in servlet with name '" + getServletName() + "'");}}else {// No need to lookup: the ModelAndView object contains the actual View object.view = mv.getView();if (view == null) {throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " +"View object in servlet with name '" + getServletName() + "'");}}// Delegate to the View object for rendering.if (logger.isDebugEnabled()) {logger.debug("Rendering view [" + view + "] in DispatcherServlet with name '" + getServletName() + "'");}try {view.render(mv.getModelInternal(), request, response);}catch (Exception ex) {if (logger.isDebugEnabled()) {logger.debug("Error rendering view [" + view + "] in DispatcherServlet with name '" +getServletName() + "'", ex);}throw ex;}}

protected View resolveViewName(String viewName, Map<String, Object> model, Locale locale,HttpServletRequest request) throws Exception {for (ViewResolver viewResolver : this.viewResolvers) {View view = viewResolver.resolveViewName(viewName, locale);if (view != null) {return view;}}return null;}

protected void initStrategies(ApplicationContext context) {initMultipartResolver(context);initLocaleResolver(context);initThemeResolver(context);initHandlerMappings(context);initHandlerAdapters(context);initHandlerExceptionResolvers(context);initRequestToViewNameTranslator(context);
//我们关注的重点initViewResolvers(context);initFlashMapManager(context);}

private void initViewResolvers(ApplicationContext context) {this.viewResolvers = null;if (this.detectAllViewResolvers) {// Find all ViewResolvers in the ApplicationContext, including ancestor contexts.Map<String, ViewResolver> matchingBeans =BeanFactoryUtils.beansOfTypeIncludingAncestors(context, ViewResolver.class, true, false);if (!matchingBeans.isEmpty()) {this.viewResolvers = new ArrayList<ViewResolver>(matchingBeans.values());// We keep ViewResolvers in sorted order.OrderComparator.sort(this.viewResolvers);}}else {try {ViewResolver vr = context.getBean(VIEW_RESOLVER_BEAN_NAME, ViewResolver.class);this.viewResolvers = Collections.singletonList(vr);}catch (NoSuchBeanDefinitionException ex) {// Ignore, we'll add a default ViewResolver later.}}// Ensure we have at least one ViewResolver, by registering// a default ViewResolver if no other resolvers are found.if (this.viewResolvers == null) {this.viewResolvers = getDefaultStrategies(context, ViewResolver.class);if (logger.isDebugEnabled()) {logger.debug("No ViewResolvers found in servlet '" + getServletName() + "': using default");}}}

/** Detect all ViewResolvers or just expect "viewResolver" bean? */private boolean detectAllViewResolvers = true;

org.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolver

<bean class="org.springframework.web.servlet.view.freemarker.FreeMarkerConfigurer"><property name="templateLoaderPath" value="/WEB-INF/views" /><property name="defaultEncoding" value="utf-8" /><property name="freemarkerSettings"><props><prop key="locale">zh_CN</prop></props></property></bean><bean class="org.springframework.web.servlet.view.freemarker.FreeMarkerViewResolver"><property name="suffix" value=".html" /><property name="contentType" value="text/html;charset=utf-8" /><property name="requestContextAttribute" value="request" /><property name="exposeRequestAttributes" value="true" /><property name="exposeSessionAttributes" value="true" /></bean>

/** Default maximum number of entries for the view cache: 1024 */public static final int DEFAULT_CACHE_LIMIT = 1024;/** The maximum number of entries in the cache */private volatile int cacheLimit = DEFAULT_CACHE_LIMIT;/** Fast access cache for Views, returning already cached instances without a global lock */private final Map<Object, View> viewAccessCache = new ConcurrentHashMap<Object, View>(DEFAULT_CACHE_LIMIT);/** Map from view key to View instance, synchronized for View creation */@SuppressWarnings("serial")private final Map<Object, View> viewCreationCache =new LinkedHashMap<Object, View>(DEFAULT_CACHE_LIMIT, 0.75f, true) {@Overrideprotected boolean removeEldestEntry(Map.Entry<Object, View> eldest) {if (size() > getCacheLimit()) {viewAccessCache.remove(eldest.getKey());return true;}else {return false;}}};

public View resolveViewName(String viewName, Locale locale) throws Exception {
//这里进行了是否进行缓存的判断，即cacheLimit是否大于0if (!isCache()) {//不进行缓存，始终每次都创建return createView(viewName, locale);}else {//viewAccessCache viewCreationCache两者的keyObject cacheKey = getCacheKey(viewName, locale);View view = this.viewAccessCache.get(cacheKey);if (view == null) {synchronized (this.viewCreationCache) {view = this.viewCreationCache.get(cacheKey);if (view == null) {// Ask the subclass to create the View object.view = createView(viewName, locale);if (view == null && this.cacheUnresolved) {view = UNRESOLVED_VIEW;}if (view != null) {this.viewAccessCache.put(cacheKey, view);this.viewCreationCache.put(cacheKey, view);if (logger.isTraceEnabled()) {logger.trace("Cached view [" + cacheKey + "]");}}}}}return (view != UNRESOLVED_VIEW ? view : null);}}

private final Map<Object, View> viewAccessCache = new ConcurrentHashMap<Object, View>(DEFAULT_CACHE_LIMIT);private final Map<Object, View> viewCreationCache =new LinkedHashMap<Object, View>(DEFAULT_CACHE_LIMIT, 0.75f, true) {@Overrideprotected boolean removeEldestEntry(Map.Entry<Object, View> eldest) {if (size() > getCacheLimit()) {viewAccessCache.remove(eldest.getKey());return true;}else {return false;}}};