DispatcherServlet類的分析

突然發現拿博客園來做筆記挺好的，不會弄丟。下面我把DispatcherServlet類的部分源代碼復制到這里，然后閱讀，把重要的地方翻譯一下，該做筆記的地方做下筆記，蹩腳英語。

 =================下面是類定義以及類注釋的一些翻譯，還需要進行修改。=================

 /**

 * Central dispatcher for HTTP request handlers/controllers, e.g. for web UI controllers
 * or HTTP-based remote service exporters. Dispatches to registered handlers for processing
 * a web request, providing convenient mapping and exception handling facilities.
 * 上文大致意思：Dispather是將HTTP請求分配給handlers/controllers的主要中心。比如對於，，，，，。 分配器注冊調用處理器到WEB請求中，為映射和異常處理提供方便。


 * <p>This servlet is very flexible: It can be used with just about any workflow, with the
 * installation of the appropriate adapter classes. It offers the following functionality
 * that distinguishes it from other request-driven web MVC frameworks:
 *　這個servlet非常的靈活。它安裝上適當的適配器類后，可以用在任何工作流程中。它提供了一下功能來區分WEB MVC框架的其他請求驅動。^o^好像不太對^o^
 * <ul>
 * <li>It is based around a JavaBeans configuration mechanism.
 * 他是基於JavaBean的配置原理。
 *
 * <li>It can use any {@link HandlerMapping} implementation - pre-built or provided as part
 * of an application - to control the routing of requests to handler objects. Default is
 * {@link org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping} and
 * {@link org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping}.
 * HandlerMapping objects can be defined as beans in the servlet's application context,
 * implementing the HandlerMapping interface, overriding the default HandlerMapping if
 * present. HandlerMappings can be given any bean name (they are tested by type).
 *
 * <li>It can use any {@link HandlerAdapter}; this allows for using any handler interface.
 * Default adapters are {@link org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter},
 * {@link org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter}, for Spring's
 * {@link org.springframework.web.HttpRequestHandler} and
 * {@link org.springframework.web.servlet.mvc.Controller} interfaces, respectively. A default
 * {@link org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter}
 * will be registered as well. HandlerAdapter objects can be added as beans in the
 * application context, overriding the default HandlerAdapters. Like HandlerMappings,
 * HandlerAdapters can be given any bean name (they are tested by type).
 *
 * <li>The dispatcher's exception resolution strategy can be specified via a
 * {@link HandlerExceptionResolver}, for example mapping certain exceptions to error pages.
 * Default are
 * {@link org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerExceptionResolver},
 * {@link org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver}, and
 * {@link org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver}.
 * These HandlerExceptionResolvers can be overridden through the application context.
 * HandlerExceptionResolver can be given any bean name (they are tested by type).
 *
 * <li>Its view resolution strategy can be specified via a {@link ViewResolver}
 * implementation, resolving symbolic view names into View objects. Default is
 * {@link org.springframework.web.servlet.view.InternalResourceViewResolver}.
 * ViewResolver objects can be added as beans in the application context, overriding the
 * default ViewResolver. ViewResolvers can be given any bean name (they are tested by type).
 *
 * <li>If a {@link View} or view name is not supplied by the user, then the configured
 * {@link RequestToViewNameTranslator} will translate the current request into a view name.
 * The corresponding bean name is "viewNameTranslator"; the default is
 * {@link org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator}.
 *
 * <li>The dispatcher's strategy for resolving multipart requests is determined by a
 * {@link org.springframework.web.multipart.MultipartResolver} implementation.
 * Implementations for Apache Commons FileUpload and Servlet 3 are included; the typical
 * choice is {@link org.springframework.web.multipart.commons.CommonsMultipartResolver}.
 * The MultipartResolver bean name is "multipartResolver"; default is none.
 *
 * <li>Its locale resolution strategy is determined by a {@link LocaleResolver}.
 * Out-of-the-box implementations work via HTTP accept header, cookie, or session.
 * The LocaleResolver bean name is "localeResolver"; default is
 * {@link org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver}.
 *
 * <li>Its theme resolution strategy is determined by a {@link ThemeResolver}.
 * Implementations for a fixed theme and for cookie and session storage are included.
 * The ThemeResolver bean name is "themeResolver"; default is
 * {@link org.springframework.web.servlet.theme.FixedThemeResolver}.
 * </ul>
 *======================================新的開始======================================
 *
 * <p><b>NOTE: The {@code @RequestMapping} annotation will only be processed if a
 * corresponding {@code HandlerMapping} (for type-level annotations) and/or
 * {@code HandlerAdapter} (for method-level annotations) is present in the dispatcher.</b>
 * This is the case by default. However, if you are defining custom {@code HandlerMappings}
 * or {@code HandlerAdapters}, then you need to make sure that a corresponding custom
 * {@code DefaultAnnotationHandlerMapping} and/or {@code AnnotationMethodHandlerAdapter}
 * is defined as well - provided that you intend to use {@code @RequestMapping}.
 * @RequestMapping 注解將會，，，，，，。但是，你還可以自定義HandlerMapping注解或HandlerAdapter，接着你要確保有一個自定義DefaultAnnotationHandlerMapping
 * 或者是AnnotationMethodHandlerAdapter 也已經定義好了--這是為你想要使用@RequestMapping提供的。
 *
 * <p><b>A web application can define any number of DispatcherServlets.</b>
 * Each servlet will operate in its own namespace, loading its own application context
 * with mappings, handlers, etc. Only the root application context as loaded by
 * {@link org.springframework.web.context.ContextLoaderListener}, if any, will be shared.
 * 一個WEB應用可以定義任何數量的DispatcherServlet。每個DispatcherServlet都只會操作它們自己的命名空間，用映射、處理器等來加載應用上下文。
 * 如果有的話，只會有一個根應用上下文，它將被ContextLoaderListener監聽器加載，它將會被共享。
 *
 * <p>As of Spring 3.1, {@code DispatcherServlet} may now be injected with a web
 * application context, rather than creating its own internally. This is useful in Servlet
 * 3.0+ environments, which support programmatic registration of servlet instances.
 * See the {@link #DispatcherServlet(WebApplicationContext)} javadoc for details.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @author Chris Beams
 * @author Rossen Stoyanchev
 * @see org.springframework.web.HttpRequestHandler
 * @see org.springframework.web.servlet.mvc.Controller
 * @see org.springframework.web.context.ContextLoaderListener
 */
@SuppressWarnings("serial")
public class DispatcherServlet extends FrameworkServlet {
 

}

 

========================下面是這個類的部分比較重要的屬性========================

 

    /** MultipartResolver used by this servlet */
    private MultipartResolver multipartResolver; 

    /** LocaleResolver used by this servlet */
    private LocaleResolver localeResolver;

    /** ThemeResolver used by this servlet */
    private ThemeResolver themeResolver;

    /** List of HandlerMappings used by this servlet */
    private List<HandlerMapping> handlerMappings;   //處理器映射列表 /** List of HandlerAdapters used by this servlet */
    private List<HandlerAdapter> handlerAdapters;   //處理器適配器列表 /** List of HandlerExceptionResolvers used by this servlet */
    private List<HandlerExceptionResolver> handlerExceptionResolvers; //處理器異常解析器列表 /** RequestToViewNameTranslator used by this servlet */
    private RequestToViewNameTranslator viewNameTranslator;

    /** FlashMapManager used by this servlet */
    private FlashMapManager flashMapManager;

    /** List of ViewResolvers used by this servlet */
    private List<ViewResolver> viewResolvers; //視圖解析器列表

 

============================下面是類的無參構造器============================

/**
     * Create a new {@code DispatcherServlet} that will create its own internal web
     * application context based on defaults and values provided through servlet
     * init-params. Typically used in Servlet 2.5 or earlier environments, where the only
     * option for servlet registration is through {@code web.xml} which requires the use
     * of a no-arg constructor.
     * <p>Calling {@link #setContextConfigLocation} (init-param 'contextConfigLocation')
     * will dictate which XML files will be loaded by the
     * {@linkplain #DEFAULT_CONTEXT_CLASS default XmlWebApplicationContext}
     * <p>Calling {@link #setContextClass} (init-param 'contextClass') overrides the
     * default {@code XmlWebApplicationContext} and allows for specifying an alternative class,
     * such as {@code AnnotationConfigWebApplicationContext}.
     * <p>Calling {@link #setContextInitializerClasses} (init-param 'contextInitializerClasses')
     * indicates which {@code ApplicationContextInitializer} classes should be used to
     * further configure the internal application context prior to refresh().
     * @see #DispatcherServlet(WebApplicationContext)
     * 
     */
    public DispatcherServlet() {
        super();
        setDispatchOptionsRequest(true);
    }

 

 =================下面是initStrategies(ApplicationContext context)方法=================

主要是初始化上面提到的部分重要屬性。

    //初始化這個DispatcherServlet使用到的策略對象。這個方法有可能會被子類覆蓋。
    protected void initStrategies(ApplicationContext context) {
        initMultipartResolver(context);
        initLocaleResolver(context);
        initThemeResolver(context);

        /* 
　　　　　 * 查找 ApplicationContext 中所有的 HandlerMapping，並按順序存儲到 handlerMappings 這個屬性中。
         * 如果一個都沒找到則將一個默認的HandlerMapping注冊到handlerMappings 屬性中。   
         */     
        initHandlerMappings(context);
 /*
 * 查找 ApplicationContext 中所有的 HandlerAdapter，並按一定的順序存儲到 handlerAdapters 這個屬性中。
 * 如果一個都沒有找到則將一個默認的 HandlerAdapter 注冊到 handlerAdapters 屬性中。
 */
 initHandlerAdapters(context);

 initHandlerExceptionResolvers(context); initRequestToViewNameTranslator(context); initViewResolvers(context); initFlashMapManager(context); }

 

 ========================下面是DispatherServlet的doService()方法==================

    /**
     * Exposes the DispatcherServlet-specific request attributes and delegates to {@link #doDispatch}
     * for the actual dispatching.
     */
　　//這才是重要的地方。

    @Override
    protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
        if (logger.isDebugEnabled()) {
            String resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult() ? " resumed" : "";
            logger.debug("DispatcherServlet with name '" + getServletName() + "'" + resumed +
                    " processing " + request.getMethod() + " request for [" + getRequestUri(request) + "]");
        }

        // Keep a snapshot of the request attributes in case of an include,
        // to be able to restore the original attributes after the include.
　　　　 //將傳進來的請求request屬性以屬性名為鍵，屬性為值，放入到一個Map對象 attributesSnapshot 中。
        //因為接下來的處理會使request的屬性放生以便下面的finally語句塊中恢復request原來的屬性。 //這個map對象起到了暫時存儲的作用。 因為接下來的處理會使request的屬性發生改變。
        Map<String, Object> attributesSnapshot = null;
        if (WebUtils.isIncludeRequest(request)) {
            attributesSnapshot = new HashMap<String, Object>();
            Enumeration<?> attrNames = request.getAttributeNames();
            while (attrNames.hasMoreElements()) {
                String attrName = (String) attrNames.nextElement();
                if (this.cleanupAfterInclude || attrName.startsWith("org.springframework.web.servlet")) {
                    attributesSnapshot.put(attrName, request.getAttribute(attrName));
                }
            }
        }

        // Make framework objects available to handlers and view objects.
　　　　　//將框架對象放到request請求的屬性中，提供給處理器對象和視圖對象使用。^o^不知道對不對，暫時這么理解^o^
        request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
        request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
        request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
        request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());

        FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
        if (inputFlashMap != null) {
            request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
        }
        request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
        request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);

        try {
            doDispatch(request, response);  //這才是重中之重
        }
        finally {
            if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
                // Restore the original attribute snapshot, in case of an include.
                if (attributesSnapshot != null) {
                    restoreAttributesAfterInclude(request, attributesSnapshot);//恢復request的屬性。
                }
            }
        }
    }

 

=========================================================================

/**
     * Process the actual dispatching to the handler.
     * <p>The handler will be obtained by applying the servlet's HandlerMappings in order.
     * The HandlerAdapter will be obtained by querying the servlet's installed HandlerAdapters
     * to find the first that supports the handler class.
     * <p>All HTTP methods are handled by this method. It's up to HandlerAdapters or handlers
     * themselves to decide which methods are acceptable.
     * @param request current HTTP request
     * @param response current HTTP response
     * @throws Exception in case of any kind of processing failure
     */
    /*
　　　　重中之重 */
    protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        HttpServletRequest processedRequest = request;
        HandlerExecutionChain mappedHandler = null;
        boolean multipartRequestParsed = false;
　　　　　//從當前request請求獲取一個WEB異步管理器，如果沒有的話就根據request請求創建一個。
        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

        try {
            ModelAndView mv = null;
            Exception dispatchException = null;

            try {
　　　　　　　　   //將request請求轉換為一個multipart請求，並且使 multipart resolver 變為可用的。如果multipart resolver不存在，則直接使用存在的請求。
                processedRequest = checkMultipart(request);
                multipartRequestParsed = (processedRequest != request);

                // Determine handler for the current request.
　　　　　　　　   //在 handlerMappings 中為請求查找對應的handler,沒有就返回null。
                mappedHandler = getHandler(processedRequest);
                if (mappedHandler == null || mappedHandler.getHandler() == null) {
                    noHandlerFound(processedRequest, response);
                    return;
                }

                // Determine handler adapter for the current request.
　　　　　　　　　 // 在handlerAdapters中為請求查找合適的HandlerAdapter，如果沒有找到就拋出異常。
                HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

                // Process last-modified header, if supported by the handler.
                String method = request.getMethod();
                boolean isGet = "GET".equals(method);
                if (isGet || "HEAD".equals(method)) {
                    long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
                    if (logger.isDebugEnabled()) {
                        logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
                    }
                    if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
                        return;
                    }
                }
　　　　　　　　　 //執行HandlerExecutionChain中的攔截器的preHandler()方法。 if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                    return;
                }

                // Actually invoke the handler.這才是真正的調用handler
　　　　　　　　　 // 使用指定的handler來處理請求。
　　　　　　　　　 //　返回一個擁有視圖名稱和模型數據的ModelAndView對象，如果請求已經直接被調用了則返回null。
                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

                if (asyncManager.isConcurrentHandlingStarted()) {
                    return;
                }

                applyDefaultViewName(processedRequest, mv);
　　　　　　　　　 //執行HandlerExecutionChain中的攔截器的postHandler()方法。
                mappedHandler.applyPostHandle(processedRequest, response, mv);
            }
            catch (Exception ex) {
                dispatchException = ex;
            }
            catch (Throwable err) {
                // As of 4.3, we're processing Errors thrown from handler methods as well,
                // making them available for @ExceptionHandler methods and other scenarios.
                dispatchException = new NestedServletException("Handler dispatch failed", err);
            }
　　　　　　　//渲染視圖,接着執行 HandlerExecutionChain 中的afterCompletion()方法。
            processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
        }
        catch (Exception ex) {
            triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
        }
        catch (Throwable err) {
            triggerAfterCompletion(processedRequest, response, mappedHandler,
                    new NestedServletException("Handler processing failed", err));
        }
        finally {
            if (asyncManager.isConcurrentHandlingStarted()) {
                // Instead of postHandle and afterCompletion
                if (mappedHandler != null) {
                    mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
                }
            }
            else {
                // Clean up any resources used by a multipart request.
　　　　　　　　　 //釋放請求占用的資源。
                if (multipartRequestParsed) {
                    cleanupMultipart(processedRequest);
                }
            }
        }
    }

 

 

=========================================================================

  /**
     * Return the HandlerExecutionChain for this request.
     * <p>Tries all handler mappings in order.
     * @param request current HTTP request
     * @return the HandlerExecutionChain, or {@code null} if no handler could be found
     */
    protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
        for (HandlerMapping hm : this.handlerMappings) {
            if (logger.isTraceEnabled()) {
                logger.trace(
                        "Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");
            }
            HandlerExecutionChain handler = hm.getHandler(request);
            if (handler != null) {
                return handler;
            }
        }
        return null;
    }

=========================================================================

 /**
     * Render the given ModelAndView.
     * <p>This is the last stage in handling a request. It may involve resolving the view by name.
     * @param mv the ModelAndView to render
     * @param request current HTTP servlet request
     * @param response current HTTP servlet response
     * @throws ServletException if view is missing or cannot be resolved
     * @throws Exception if there's a problem rendering the view
     */
    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 {
            if (mv.getStatus() != null) {
                response.setStatus(mv.getStatus().value());
            }
            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;
        }
    }

 

=========================================================================

 /**
     * Resolve the given view name into a View object (to be rendered).
     * <p>The default implementations asks all ViewResolvers of this dispatcher.
     * Can be overridden for custom resolution strategies, potentially based on
     * specific model attributes or request parameters.
     * @param viewName the name of the view to resolve
     * @param model the model to be passed to the view
     * @param locale the current locale
     * @param request current HTTP servlet request
     * @return the View object, or {@code null} if none found
     * @throws Exception if the view cannot be resolved
     * (typically in case of problems creating an actual View object)
     * @see ViewResolver#resolveViewName
     */
    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;
    }

 

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