本章開始進入另外一重要的組件,即視圖組件,Spring MVC處理視圖組件使用兩個主要的接口是ViewResolver和View。根據名稱可知,ViewResolver即視圖解析器,其做用是把邏輯視圖名稱解析爲真正的視圖,而後經過View對象進行渲染。View接口的做用是用於處理視圖進行渲染。web
延用以前的介紹流程,本章分兩部分進行闡述:啓動初始化和請求處理。app
本系列文章是基於Spring5.0.5RELEASE。jsp
Spring MVC初始化視圖解析器策略與初始化其餘策略同樣,其入口是DispatcherSerlvet的initStrategies(context)方法,代碼以下:學習
/** *初始化策略對象 */ protected void initStrategies(ApplicationContext context) { initMultipartResolver(context); initLocaleResolver(context); initThemeResolver(context); initHandlerMappings(context); initHandlerAdapters(context); initHandlerExceptionResolvers(context); initRequestToViewNameTranslator(context); // 初始化視圖解析器ViewResolver initViewResolvers(context); initFlashMapManager(context); }
看過以前文章的能夠了解,此方法是Spring MVC初始化策略組件的入口。針對視圖解析器組件,調用initViewResolver(context)方法,加載視圖處理策略,該方法源碼以下:this
private void initViewResolvers(ApplicationContext context) { // viewResolvers是視圖解析器集合,接收到用戶請求時,從該屬性變量中獲取到Spring MVC使用的視圖解析器 this.viewResolvers = null; // 是否從Spring上下文中加載ViewResolver,detectAllViewResolvers屬性變量默認爲true,可在web部署描述文件中修改 if (this.detectAllViewResolvers) { // Find all ViewResolvers in the ApplicationContext, including ancestor contexts. // 按接口類型ViewResolver查找所有 // key爲bean的id(name),value爲bean的class對象 Map<String, ViewResolver> matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(context, ViewResolver.class, true, false); if (!matchingBeans.isEmpty()) { this.viewResolvers = new ArrayList<>(matchingBeans.values()); // We keep ViewResolvers in sorted order. // 對ViewResolver進行排序,經過Ordered接口實現 AnnotationAwareOrderComparator.sort(this.viewResolvers); } } else { try { // 從Spring上下文中加載指定名字爲"viewResolver"的bean,做爲視圖解析器 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. // 爲了確保至少有一個ViewResolver視圖解析器,Spring MVC配置了默認的ViewResolver // 在DispatcherServlet.properties文件中定義,默認爲InternalResourceViewResolver if (this.viewResolvers == null) { this.viewResolvers = getDefaultStrategies(context, ViewResolver.class); if (logger.isDebugEnabled()) { logger.debug("No ViewResolvers found in servlet '" + getServletName() + "': using default"); } } }
至此,Spring MVC即完成加載初始化ViewResolver視圖解析器,即Spring MVC以具有解析處理邏輯視圖名稱的能力。url
ViewResolver的使用是指用戶發起請求到Spring,Spring MVC通過HandlerMapping查找處理的handler,而後經過HandlerAdapter進行適配後處理用戶請求,返回ModelAndView,最後使用ViewResolver對ModelAndView進行解析,即把邏輯視圖名解析爲真正的視圖對象,由視圖對象進行渲染的過程。spa
用戶的請求處理流程由DispatcherServlet的doDispatcher(request,response)方法進行控制,主要代碼以下:debug
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { ... ... // 找到請求對應的handler mappedHandler = getHandler(processedRequest); ... ... // 找到對應handler的適配器 HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler()); ... ... // 執行用戶請求的攔截器前置處理方法 if (!mappedHandler.applyPreHandle(processedRequest, response)) { return; } // 調用實際的handler處理方法 mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); ... ... // 設置默認的邏輯視圖名稱 // 若是handler返回null或者ViewName屬性爲null時,Spring進行取視圖規則爲:前綴+url+後綴 // 好比訪問url爲:http://localhost:8086/test,前綴配置/WEB-INF/jsp,後綴配置爲.jsp,那麼最終查找的是:/WEB-INF/jsp/test.jsp applyDefaultViewName(processedRequest, mv); // 執行用戶請求的攔截器後置處理方法 mappedHandler.applyPostHandle(processedRequest, response, mv); ... ... // processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException); } /* *處理結果 */ private void processDispatchResult(HttpServletRequest request, HttpServletResponse response, @Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv, @Nullable Exception exception) throws Exception { boolean errorView = false; // 異常處理 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? // 調用render方法 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 forward return; } if (mappedHandler != null) { mappedHandler.triggerAfterCompletion(request, response, null); } } /* *渲染ModelAndView */ 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 != null ? this.localeResolver.resolveLocale(request) : request.getLocale()); response.setLocale(locale); View view; // 獲取邏輯視圖名稱 String viewName = mv.getViewName(); if (viewName != null) { // We need to resolve the view name. // 根據邏輯視圖名解析視圖,返回View對象 // 此處是視圖解析器使用入口,見下面的方法 view = resolveViewName(viewName, 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 { if (mv.getStatus() != null) { response.setStatus(mv.getStatus().value()); } // 調用View的render方法進行視圖渲染 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; } } @Nullable protected View resolveViewName(String viewName, @Nullable Map<String, Object> model, Locale locale, HttpServletRequest request) throws Exception { if (this.viewResolvers != null) { for (ViewResolver viewResolver : this.viewResolvers) { // 調用ViewResovler接口入口方法 View view = viewResolver.resolveViewName(viewName, locale); if (view != null) { return view; } } } return null; }
本章概述了Spring MVC加載視圖解析器策略,而且找到了ViewResolver的入口方法,下面的章節繼續學習ViewResolver接口的實現類。code
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