DispatcherServlet类的分析
突然发现拿博客园来做笔记挺好的，不会弄丢。下面我把DispatcherServlet类的部分源代码复制到这里，然后阅读，把重要的地方翻译一下，该做笔记的地方做下笔记，蹩脚英语。
=================下面是类定义以及类注释的一些翻译，还需要进行修改。=================
/**
* 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是将HTTP请求分配给handlers/controllers的主要中心。比如对于，，，，，。 分配器注册调用处理器到WEB请求中，为映射和异常处理提供方便。
* <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: * 这个servlet非常的灵活。它安装上适当的适配器类后，可以用在任何工作流程中。它提供了一下功能来区分WEB MVC框架的其他请求驱动。^o^好像不太对^o^ * <ul> * <li>It is based around a JavaBeans configuration mechanism. * 他是基于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> *======================================新的开始======================================
* * <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 注解将会，，，，，，。但是，你还可以自定义HandlerMapping注解或HandlerAdapter，接着你要确保有一个自定义DefaultAnnotationHandlerMapping
* 或者是AnnotationMethodHandlerAdapter 也已经定义好了--这是为你想要使用@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. * 一个WEB应用可以定义任何数量的DispatcherServlet。每个DispatcherServlet都只会操作它们自己的命名空间，用映射、处理器等来加载应用上下文。
* 如果有的话，只会有一个根应用上下文，它将被ContextLoaderListener监听器加载，它将会被共享。
* * <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 {
}
========================下面是这个类的部分比较重要的属性========================
/** 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; //处理器映射列表 /** List of HandlerAdapters used by this servlet */ private List<HandlerAdapter> handlerAdapters; //处理器适配器列表 /** List of HandlerExceptionResolvers used by this servlet */ private List<HandlerExceptionResolver> handlerExceptionResolvers; //处理器异常解析器列表 /** 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; //视图解析器列表
============================下面是类的无参构造器============================
/** * 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属性。
//初始化这个DispatcherServlet使用到的策略对象。这个方法有可能会被子类覆盖。 protected void initStrategies(ApplicationContext context) { initMultipartResolver(context); initLocaleResolver(context); initThemeResolver(context);
/*
* 查找 ApplicationContext 中所有的 HandlerMapping，并按顺序存储到 handlerMappings 这个属性中。
* 如果一个都没找到则将一个默认的HandlerMapping注册到handlerMappings 属性中。
*/
initHandlerMappings(context);
/*
* 查找 ApplicationContext 中所有的 HandlerAdapter，并按一定的顺序存储到 handlerAdapters 这个属性中。
* 如果一个都没有找到则将一个默认的 HandlerAdapter 注册到 handlerAdapters 属性中。
*/
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. */ //这才是重要的地方。 @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. //将传进来的请求request属性以属性名为键，属性为值，放入到一个Map对象 attributesSnapshot 中。
//因为接下来的处理会使request的属性放生以便下面的finally语句块中恢复request原来的属性。 //这个map对象起到了暂时存储的作用。 因为接下来的处理会使request的属性发生改变。 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. //将框架对象放到request请求的属性中，提供给处理器对象和视图对象使用。^o^不知道对不对，暂时这么理解^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); //这才是重中之重 } finally { if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) { // Restore the original attribute snapshot, in case of an include. if (attributesSnapshot != null) { restoreAttributesAfterInclude(request, attributesSnapshot);//恢复request的属性。 } } } }
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/** * 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; //从当前request请求获取一个WEB异步管理器，如果没有的话就根据request请求创建一个。 WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request); try { ModelAndView mv = null; Exception dispatchException = null; try { //将request请求转换为一个multipart请求，并且使 multipart resolver 变为可用的。如果multipart resolver不存在，则直接使用存在的请求。 processedRequest = checkMultipart(request); multipartRequestParsed = (processedRequest != request); // Determine handler for the current request. //在 handlerMappings 中为请求查找对应的handler,没有就返回null。 mappedHandler = getHandler(processedRequest); if (mappedHandler == null || mappedHandler.getHandler() == null) { noHandlerFound(processedRequest, response); return; } // Determine handler adapter for the current request. // 在handlerAdapters中为请求查找合适的HandlerAdapter，如果没有找到就抛出异常。 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; } } //执行HandlerExecutionChain中的拦截器的preHandler()方法。 if (!mappedHandler.applyPreHandle(processedRequest, response)) { return; } // Actually invoke the handler.这才是真正的调用handler // 使用指定的handler来处理请求。 // 返回一个拥有视图名称和模型数据的ModelAndView对象，如果请求已经直接被调用了则返回null。 mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); if (asyncManager.isConcurrentHandlingStarted()) { return; } applyDefaultViewName(processedRequest, mv); //执行HandlerExecutionChain中的拦截器的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); } //渲染视图,接着执行 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. //释放请求占用的资源。 if (multipartRequestParsed) { cleanupMultipart(processedRequest); } } } }
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/** * 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; }
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/** * 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; } }
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/** * 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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