Springmvc請求處理流程

HttpServletBean

httpServletBean中Environment使用的是StandardServletEnvironment

StandardServletEnvironment

其中propertySources屬性封裝了以下信息：

• servletContext 和 servletConfig
• jndiProperty
• 系統環境變量
• 系統屬性

//frameworkServlet中初始化
@Override
public void initPropertySources(ServletContext servletContext, ServletConfig servletConfig) {
  WebApplicationContextUtils.initServletPropertySources(
    this.getPropertySources(), servletContext, servletConfig);//servletContext 和 servletConfig
}

//AbstractEnvironment 構造方法中調用，構造StandardServletEnvironment對象時就有了。
@Override
protected void customizePropertySources(MutablePropertySources propertySources) {
   propertySources.addLast(new StubPropertySource(SERVLET_CONFIG_PROPERTY_SOURCE_NAME));
   propertySources.addLast(new StubPropertySource(SERVLET_CONTEXT_PROPERTY_SOURCE_NAME));
   if (JndiLocatorDelegate.isDefaultJndiEnvironmentAvailable()) {
      propertySources.addLast(new JndiPropertySource(JNDI_PROPERTY_SOURCE_NAME));//jndiProperty
   }
   super.customizePropertySources(propertySources);
}

@Override
protected void customizePropertySources(MutablePropertySources propertySources) {
   propertySources.addLast(new MapPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties()));//系統屬性
   propertySources.addLast(new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME, getSystemEnvironment()));//系統環境變量
}

init()

@Override
public final void init() throws ServletException {
   if (logger.isDebugEnabled()) {
      logger.debug("Initializing servlet '" + getServletName() + "'");
   }

   // Set bean properties from init parameters.
   try {
      PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
      BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);//this就是以後的DispatcherServlet
      ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
      bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));//註冊Editor，複合resource類的，就用ResourceEditor來編輯
      initBeanWrapper(bw);
      bw.setPropertyValues(pvs, true);//將ServletConfig設置到dispatcherServlet
   }
   catch (BeansException ex) {
      logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
      throw ex;
   }

   // Let subclasses do whatever initialization they like.
   initServletBean();//模版方法

   if (logger.isDebugEnabled()) {
      logger.debug("Servlet '" + getServletName() + "' configured successfully");
   }
}

HttpServletBean主要做用

• 定義Environment
• 設置ServletConfig

FrameworkServlet

implements ApplicationContextAware

從spring中獲取WebApplicationContext

initServletBean()

@Override
protected final void initServletBean() throws ServletException {
...
   try {
      this.webApplicationContext = initWebApplicationContext();
      initFrameworkServlet();
   }
   catch (ServletException ex) {
      this.logger.error("Context initialization failed", ex);
      throw ex;
   }
...
}

protected WebApplicationContext initWebApplicationContext() {
  //獲取spring的容器，從ServletContext#getAttribute(WebApplicationContext.class.getName() + ".ROOT")
   WebApplicationContext rootContext =
         WebApplicationContextUtils.getWebApplicationContext(getServletContext());
   WebApplicationContext wac = null;

   if (this.webApplicationContext != null) {
      // A context instance was injected at construction time -> use it
      wac = this.webApplicationContext;
      if (wac instanceof ConfigurableWebApplicationContext) {
         ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
         if (!cwac.isActive()) {
            // The context has not yet been refreshed -> provide services such as
            // setting the parent context, setting the application context id, etc
            if (cwac.getParent() == null) {
               // The context instance was injected without an explicit parent -> set
               // the root application context (if any; may be null) as the parent
              //將spring容器設置爲springmvc容器的父容器
               cwac.setParent(rootContext);
            }
            configureAndRefreshWebApplicationContext(cwac);
         }
      }
   }
  //this.webApplicationContext = null & wac = null 是什麼狀況？
   if (wac == null) {
      // No context instance was injected at construction time -> see if one
      // has been registered in the servlet context. If one exists, it is assumed
      // that the parent context (if any) has already been set and that the
      // user has performed any initialization such as setting the context id
     //經過配置servlet中的contextAttribute參數，從ServletContext中獲取指定名字的webApplicationContext
      wac = findWebApplicationContext();
   }
   if (wac == null) {
      // No context instance is defined for this servlet -> create a local one
      wac = createWebApplicationContext(rootContext);
   }

   if (!this.refreshEventReceived) {
      // Either the context is not a ConfigurableApplicationContext with refresh
      // support or the context injected at construction time had already been
      // refreshed -> trigger initial onRefresh manually here.
     // 留給dispatcherServlet
      onRefresh(wac);
   }

   if (this.publishContext) {
      // Publish the context as a servlet context attribute.
      // FrameworkServlet.class.getName() + ".CONTEXT." + getServletName();
      String attrName = getServletContextAttributeName();
      getServletContext().setAttribute(attrName, wac);
      if (this.logger.isDebugEnabled()) {
         this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
               "' as ServletContext attribute with name [" + attrName + "]");
      }
   }

   return wac;
}

做用：

• 初始化WebApplicationContext 從ServletContext中獲取
• initFrameworkServlet模版方法

servlet的webApplicationContext

1. 已經構造好了webApplicationContext，在servlet構造方法中傳入現有的對象。（主要用於servlet3.0之後，ServletContext.addServlet）
2. webApplication已經在ServletContext中了。能夠經過配置來從servletContext中根據contextAttribute獲取現有webApplicationContext

<servlet>
  <servlet-name>spring</servlet-name>
  <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
  <init-param>
    <!--配置contextAttribute，從servletContext中找hehe的webApplicationContext-->
    <param-name>contextAttribute</param-name> 
    <param-value>hehe</param-value>
  </init-param>
  <init-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath:spring-mvc.xml</param-value>
  </init-param>
  <load-on-startup>1</load-on-startup>
  <async-supported>true</async-supported>
</servlet>

3. 本身建立（正常狀況）

webApplicationContext 中的內容

• environment
• parent
• contextConfigLocation ：web.xml中配置，默認WEB-INFO/[servletname]-Servlet.xml
• servletContext
• servletConfig
• namespace
• applicationListener : ContextRefreshedEvent監聽器，收到event後調用onRefresh() 方法
• postProcessWebApplicationContext() 後置處理

重寫doGet doPost.....

將doXXX方法所有交由processRequest() 方法。doOptions 和 doTrace 根據參數判斷本身處理仍是交給父類

processRequest

• 對LocaleContext和RequestAttributes設置和恢復
• doService()
• 處理完後發佈publishRequestHandledEvent

ServletRequestAttributes封裝了request，能夠從request和session中取值。

requestAttributes.requestCompleted();執行後，不能再對requestAttributes進行操做。

LocaleContextHolder/RequestContextHolder

//根據request設置LocaleContextHolder/RequestContextHolder,可提供locale和request，在service層。
initContextHolders(request, localeContext, requestAttributes);

localeContextHolder、inheritableLocaleContextHolder能夠被子線程繼承？？？

沒搞懂localeContextHolder inheritableLocaleContextHolder兩個ThreadLocal變量的做用，但願大神幫忙解答。

resetContextHolders(request, previousLocaleContext, previousAttributes); //爲何要恢復？怕影響Servlet外面的filter工做，可能有什麼修改須要恢復？

publishRequestHandledEvent

配置：web.xml中配置springmvc servlet時配置，默認true。

用法：能夠用來記錄日誌。

DispatcherServlet

初始化各類組件init()

• MutipartResolver
• LocaleResolver
• ThemeResolver
• HandlerMappings
• HandlerAdapters
• HandlerExceptionResolvers
• RequestToViewNameTranslator
• ViewResolvers
• FlashMapManager

doService()

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

   // Keep a snapshot of the request attributes in case of an include,
   // to be able to restore the original attributes after the include.
  //判斷是不是include請求，若是是則對request作快照備份，結束後還原
   Map<String, Object> attributesSnapshot = null;
   if (WebUtils.isIncludeRequest(request)) {
      logger.debug("Taking snapshot of request attributes before include");
      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.
  //設置屬性
   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());

  //後面3個和flashMap有關。用於redirect傳遞參數。
   FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
   if (inputFlashMap != null) {
     //先取出flashmap放入INPUT_FLASH_MAP_ATTRIBUTE，再放入model中。在Controller中可使用。
     //RedirectAttributes.addFlashAttribute() 將參數添加到session中
     //RedirectAttributes.addAttribute() 將參數拼接到url後。
      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);
   }
   finally {
      if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
         return;
      }
      // Restore the original attribute snapshot, in case of an include.
      if (attributesSnapshot != null) {
         restoreAttributesAfterInclude(request, attributesSnapshot);
      }
   }
}

• 設置request一些屬性
• 處理include請求快照
• doDispatch()

doDispatch()

• 根據request找handler
• 根據handler找HandlerAdapter
• 用Adapter處理handler
• processDispathResult() 處理結果，包括找到view並渲染。

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
   HttpServletRequest processedRequest = request;
   HandlerExecutionChain mappedHandler = null;
   boolean multipartRequestParsed = false;

   WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

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

      try {
        //判斷是不是Multipart 請求,用到MultipartResolver
         processedRequest = checkMultipart(request);
         multipartRequestParsed = processedRequest != request;

         // Determine handler for the current request.
        //根據request獲取handler，用到handlerMapping
         mappedHandler = getHandler(processedRequest);
         if (mappedHandler == null || mappedHandler.getHandler() == null) {
            noHandlerFound(processedRequest, response);
            return;
         }

         // Determine handler adapter for the current request.
        //獲取adatper
         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()) {
               String requestUri = urlPathHelper.getRequestUri(request);
               logger.debug("Last-Modified value for [" + requestUri + "] is: " + lastModified);
            }
            if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
               return;
            }
         }
		
        //interceptor#perHandler
         if (!mappedHandler.applyPreHandle(processedRequest, response)) {
            return;
         }

         try {
            // Actually invoke the handler.
            mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
         }
         finally {
           //異步處理，則直接返回
            if (asyncManager.isConcurrentHandlingStarted()) {
               return;
            }
         }

         applyDefaultViewName(request, mv);
        //interceptor#postHandler
         mappedHandler.applyPostHandle(processedRequest, response, mv);
      }
      catch (Exception ex) {
         dispatchException = ex;
      }
      processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
   }
   catch (Exception ex) {
      triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
   }
   catch (Error err) {
      triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err);
   }
   finally {
      if (asyncManager.isConcurrentHandlingStarted()) {
         // Instead of postHandle and afterCompletion
         mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
         return;
      }
      // Clean up any resources used by a multipart request.
      if (multipartRequestParsed) {
         cleanupMultipart(processedRequest);
      }
   }
}

processDispatchResult()

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);
        //用到HanlderExceptionResolver
         mv = processHandlerException(request, response, handler, exception);
         errorView = (mv != null);
      }
   }

   // Did the handler return a view to render?
   if (mv != null && !mv.wasCleared()) {
     //渲染頁面，用到themeResolver
      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");
      }
   }

  //異步
   if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
      // Concurrent handling started during a forward
      return;
   }

   if (mappedHandler != null) {
     //觸發Interceptor#afterCompletion()
      mappedHandler.triggerAfterCompletion(request, response, null);
   }
}