<servlet>
    <servlet-name>spring-servlet</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>classpath:springmvc-servlet.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>

  <servlet-mapping>
    <servlet-name>spring-servlet</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>

@Override
  protected final void initServletBean() throws ServletException {
    getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
    if (this.logger.isInfoEnabled()) {
      this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
    }
    long startTime = System.currentTimeMillis();

    try {
     // 初始化spring-servlet容器
      this.webApplicationContext = initWebApplicationContext();
      initFrameworkServlet();
    }
    catch (ServletException ex) {
      this.logger.error("Context initialization failed", ex);
      throw ex;
    }
    catch (RuntimeException ex) {
      this.logger.error("Context initialization failed", ex);
      throw ex;
    }

    if (this.logger.isInfoEnabled()) {
      long elapsedTime = System.currentTimeMillis() - startTime;
      this.logger.info("FrameworkServlet '" + getServletName() + "': initialization completed in " +
          elapsedTime + " ms");
    }
  }

protected WebApplicationContext initWebApplicationContext() {
// 查看是否在servlet上下文有所有容器需要继承的根Web容器
    WebApplicationContext rootContext =
        WebApplicationContextUtils.getWebApplicationContext(getServletContext());
    WebApplicationContext wac = null;
    // 如果容器已经加载
    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
            cwac.setParent(rootContext);
          }
          configureAndRefreshWebApplicationContext(cwac);
        }
      }
    }
    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
      wac = findWebApplicationContext();
    }
    if (wac == null) {
      // 创建容器
      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.
      onRefresh(wac);
    }

    if (this.publishContext) {
      // Publish the context as a servlet context attribute.
      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;
  }

protected WebApplicationContext createWebApplicationContext(ApplicationContext parent) {
    Class<?> contextClass = getContextClass();
    if (this.logger.isDebugEnabled()) {
      this.logger.debug("Servlet with name '" + getServletName() +
          "' will try to create custom WebApplicationContext context of class '" +
          contextClass.getName() + "'" + ", using parent context [" + parent + "]");
    }
    // 判断是否是可配置的容器
    if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
      throw new ApplicationContextException(
          "Fatal initialization error in servlet with name '" + getServletName() +
          "': custom WebApplicationContext class [" + contextClass.getName() +
          "] is not of type ConfigurableWebApplicationContext");
    }
    // 如果找到目标容器，并且可配置，然后就开始获取配置文件并开始初始化
    ConfigurableWebApplicationContext wac =
        (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);

    wac.setEnvironment(getEnvironment());
    wac.setParent(parent);
    wac.setConfigLocation(getContextConfigLocation());
    // 这里是获取配置文件和完成初始化web容器的入口
    configureAndRefreshWebApplicationContext(wac);

    return wac;
  }

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {
// 给容器设置一个id
    if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
      // The application context id is still set to its original default value
      // -> assign a more useful id based on available information
      if (this.contextId != null) {
        wac.setId(this.contextId);
      }
      else {
        // Generate default id...
        wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
            ObjectUtils.getDisplayString(getServletContext().getContextPath()) + '/' + getServletName());
      }
    }

    wac.setServletContext(getServletContext());
    wac.setServletConfig(getServletConfig());
    wac.setNamespace(getNamespace());
    wac.addApplicationListener(new SourceFilteringListener(wac, new ContextRefreshListener()));

    // The wac environment's #initPropertySources will be called in any case when the context
    // is refreshed; do it eagerly here to ensure servlet property sources are in place for
    // use in any post-processing or initialization that occurs below prior to #refresh
    ConfigurableEnvironment env = wac.getEnvironment();
    if (env instanceof ConfigurableWebEnvironment) {
      ((ConfigurableWebEnvironment) env).initPropertySources(getServletContext(), getServletConfig());
    }
    /* 这里在容器被激活后，
    并且容器还没完成初始化之前可以对容器的相关配置做一些修改，
    默认给了空实现，
    这里子类可以去重写，能够获得在容器初始化之前做  一些处理*/
    postProcessWebApplicationContext(wac);
    // 这里讲容器的初始化信息放到一个列表
    applyInitializers(wac);
    // 这里就开始web容器的初始化
    wac.refresh();
  }

public void refresh() throws BeansException, IllegalStateException {
    synchronized (this.startupShutdownMonitor) {
      // 这里主要加载了容器当中一些从其他配置文件读取的变量
      prepareRefresh();

      // 获取容器本身
      ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

      // 这里完成一些基础组件的依赖
      prepareBeanFactory(beanFactory);

      try {
        // 添加 容器初始化之前的前置处理
        postProcessBeanFactory(beanFactory);

        // 调用 前置处理器，其中包含invokeBeanDefinitionRegistryPostProcessors与invokeBeanFactoryPostProcessors两类前置处理器的调用
        invokeBeanFactoryPostProcessors(beanFactory);

        // 注册bean被创建之前的前置处理器
        registerBeanPostProcessors(beanFactory);

        // 初始化容器的编码源        
        initMessageSource();

        // 初始化一些事件监听器
        initApplicationEventMulticaster();

        // Initialize other special beans in specific context subclasses.
        onRefresh();

        // 注册容器监听器
        registerListeners();

        // 初始化所有非懒加载的beans
        finishBeanFactoryInitialization(beanFactory);

        // Last step: 事件通知关心容器加载的相关组件
        finishRefresh();
      }

      // 部分代码省略
      }
    }
  }

protected void initStrategies(ApplicationContext context) {
    initMultipartResolver(context);
    initLocaleResolver(context);
    initThemeResolver(context);
    // 获取所有的RequestMappings
    initHandlerMappings(context);
    // 不同handler的适配器
    initHandlerAdapters(context);
    // 异常解析器
    initHandlerExceptionResolvers(context);
    initRequestToViewNameTranslator(context);
    initViewResolvers(context);
    initFlashMapManager(context);
  }

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 {
        processedRequest = checkMultipart(request);
        multipartRequestParsed = (processedRequest != request);

        // 这里获取当前请求的处理handler
        mappedHandler = getHandler(processedRequest, false);
        if (mappedHandler == null || mappedHandler.getHandler() == null) {
          noHandlerFound(processedRequest, response);
          return;
        }

        /* 因为handler可以是任何类，
        但是我们的DispacherServlet需要一个统一的处理接口，这个接口就是HandlerAdapter,
        不同的HandlerMapping可以获取到各种各样的Handler，
        这个handler最后都必须得到HandlerAdapter的支持才能被DispacherServlet所调用。
        扩充一个新的HandlerMapping只需要添加一个新的HandlerAdatper即可，有点抽象工厂模式的味道*/
        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;
          }
        }

        if (!mappedHandler.applyPreHandle(processedRequest, response)) {
          return;
        }

        // Actually invoke the handler.
        mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

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

        applyDefaultViewName(request, mv);
        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
        if (mappedHandler != null) {
          mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
        }
      }
      else {
        // Clean up any resources used by a multipart request.
        if (multipartRequestParsed) {
          cleanupMultipart(processedRequest);
        }
      }
    }
  }

protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
// 这里获取多个映射方式，一旦找到合适的处理请求的handler即返回
    for (HandlerMapping hm : this.handlerMappings) {
      if (logger.isTraceEnabled()) {
        logger.trace(
            "Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");
      }
      // HandlerExecutionChain包含了
      HandlerExecutionChain handler = hm.getHandler(request);
      if (handler != null) {
        return handler;
      }
    }
    return null;
  }

processDispatchResult(HttpServletRequest request, HttpServletResponse response,
      HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception)