SpringMVC 源码解析

前言

年初面试时接触到一道面试题，在聊到SpringMVC时提到了SpringMVC的开发者为何要设计父子容器呢，又或者说是父子容器的设计有什么更实际的作用呢？

首先要理解对于一个web应用，当其部署在web容器上时，容器会为其提供一个全局上下文环境ServletContext，这个上下文环境将为后续的Spring提供宿主环境。

SpringMVC工作流程

DispatcherServlet上下文继承关系

SpringMVC设计的父子容器

父子容器配置文件

--在web.xml中配置，两个重要的xml:applicationContext.xml和SpringMVC-conf.xml
<context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath*:applictionContext.xml</param-value>
</context-param>
<listener>
   <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
  
<servlet>
    <servlet-name>dispatcher-servlet</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>classpath*:springMVC-conf.xml</param-value>
    </init-param>
</servlet>
  
<servlet-mapping>
  <servlet-name>dispatcher-servlet</servlet-name>
  <url-pattern>/*</url-pattern>
</servlet-mapping>

父子容器的设计目的

根据SpringMVC的官方解释，父（根）容器主要包括一些基础脚手架的bean，比如Pool、DataSource、Dao、Service。目的是在不同的Servlet实例之间共享。这些不同的bean可以在子容器中重写。

而子容器主要包括一些Controller、View等一些web相关的bean。 

DispatcherServlet源码分析

既然SpringMVC中同时包含Spring容器和SpringMVC容器，那么这两个容器都是在什么时候初始化呢？

根容器初始化

首先，根容器是通过ServletContext监听器进行创建，默认的监听器为ContextLoaderListener，当web应用启动时，会调用监听器的 contextInitialized 方法。

那么根容器的初始化就从 ContextLoaderListener 类说起吧，，Spring官方对该类的描述是启动监听器去启动和关闭Spring的root WebApplicationContext（翻译的实在有点蹩脚）。

public class ContextLoaderListener extends ContextLoader implements ServletContextListener {
    public ContextLoaderListener() {
    }

    public ContextLoaderListener(WebApplicationContext context) {
        super(context);
    }

    //===初始化root WebApplicationContext===
    @Override
    public void contextInitialized(ServletContextEvent event) {
        initWebApplicationContext(event.getServletContext());
    }

    @Override
    public void contextDestroyed(ServletContextEvent event) {
        closeWebApplicationContext(event.getServletContext());
        ContextCleanupListener.cleanupAttributes(event.getServletContext());
    }
}

//ContextLoader.java
public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
    //初始化Spring容器时如果发现servlet 容器中已存在根Spring容根器则抛出异常，证明rootWebApplicationContext只能有一个。
    if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {
        throw new IllegalStateException(
                "Cannot initialize context because there is already a root application context present - " +
                "check whether you have multiple ContextLoader* definitions in your web.xml!");
    }

    try {
        //创建webApplicationContext实例
        if (this.context == null) {
            this.context = createWebApplicationContext(servletContext);
        }
        if (this.context instanceof ConfigurableWebApplicationContext) {
            ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;
            if (!cwac.isActive()) {
                if (cwac.getParent() == null) {
                    ApplicationContext parent = loadParentContext(servletContext);
                    cwac.setParent(parent);
                }
                //配置WebApplicationContext
                configureAndRefreshWebApplicationContext(cwac, servletContext);
            }
        }
        
        /**
           把生成的webApplicationContext设置成root WebApplicationContext。保存在ServletContext上下文中。
           下一步初始化MVC ApplicationContext时需要从ServletContext取出根上下文作为其父上下文。
        **/ 
        servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);

        ClassLoader ccl = Thread.currentThread().getContextClassLoader();
        if (ccl == ContextLoader.class.getClassLoader()) {
            currentContext = this.context;
        }
        else if (ccl != null) {
            currentContextPerThread.put(ccl, this.context);
        }
        
        return this.context;
    }
    catch (RuntimeException | Error ex) {
        servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);
        throw ex;
    }
}

以上代码主要完成两个功能：创建实例WebApplicationContext实例、把所创建的WebApplicationContext设置为根上下文，也就是设置成为ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE的值。

MVC容器初始化

大家知道Servlet生命周期都是从init方法开始，desctory方法结束，由jvm负责垃圾回收。而DispatcherServlet也是一个普通的Servlet，先看一下DispatcherServlet的继承关系图，对整个继承关系有个了解。

既然说起Servlet，那就从Servlet的初始化（init）方法入手

//HttpServletBean.java
@Override
public final void init() throws ServletException {

    PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
    if (!pvs.isEmpty()) {
        try {
            BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
            ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
            bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
            initBeanWrapper(bw);
            bw.setPropertyValues(pvs, true);
        }
        catch (BeansException ex) {
            throw ex;
        }
    }

    //交给子类重写
    initServletBean();
}

//FrameworkServlet.java
@Override
protected final void initServletBean() throws ServletException {
    try {
        this.webApplicationContext = initWebApplicationContext();
        initFrameworkServlet();
    }
    catch (ServletException | RuntimeException ex) {
        throw ex;
    }
}

//FrameworkServlet.java
//初始化MVC容器
protected WebApplicationContext initWebApplicationContext() {
    //从ServletContext取出根上下文
    WebApplicationContext rootContext =
            WebApplicationContextUtils.getWebApplicationContext(getServletContext());
    WebApplicationContext wac = null;

    if (this.webApplicationContext != null) {
        wac = this.webApplicationContext;
        if (wac instanceof ConfigurableWebApplicationContext) {
            ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
            if (!cwac.isActive()) {
                if (cwac.getParent() == null) {
                    cwac.setParent(rootContext);
                }
                configureAndRefreshWebApplicationContext(cwac);
            }
        }
    }
    if (wac == null) {
        wac = findWebApplicationContext();
    }
    
    //如果还没有webApplicatioinContext，创建webApplicationContext
    if (wac == null) {
        wac = createWebApplicationContext(rootContext);
    }

    //子类自定义对servlet子上下文后续操作，在DispatcherServlet中实现
    if (!this.refreshEventReceived) {
        synchronized (this.onRefreshMonitor) {
            //执行子类扩展方法onRefresh，在DispatcherServlet内初始化所有web相关组件
            onRefresh(wac);
        }
    }

    //发布servlet子上下文到ServletContext
    if (this.publishContext) {
        String attrName = getServletContextAttributeName();
        //将servlet子上下文以org.springframework.web.servlet.FrameworkServlet.CONTEXT. + servletName的属性名称注册到ServletContext中
        getServletContext().setAttribute(attrName, wac);
    }

    return wac;
}

protected WebApplicationContext createWebApplicationContext(@Nullable WebApplicationContext parent) {
    return createWebApplicationContext((ApplicationContext) parent);
}

protected WebApplicationContext createWebApplicationContext(@Nullable ApplicationContext parent) {
    //获取WebApplicationContext实现类，此处其实就是XmlWebApplicationContext
    Class<?> contextClass = getContextClass();
    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");
    }
    
    //生成XmlWebApplicationContext实例
    ConfigurableWebApplicationContext wac =
            (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);

    wac.setEnvironment(getEnvironment());
    //设置根容器为父容器 
    wac.setParent(parent);
    String configLocation = getContextConfigLocation();
    if (configLocation != null) {
        //设置配置文件
        wac.setConfigLocation(configLocation);
    }
    
    //配置webApplicationContext
    configureAndRefreshWebApplicationContext(wac);

    return wac;
}

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {
    if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
        if (this.contextId != null) {
            wac.setId(this.contextId);
        }
        else {
            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()));

    ConfigurableEnvironment env = wac.getEnvironment();
    if (env instanceof ConfigurableWebEnvironment) {
        ((ConfigurableWebEnvironment) env).initPropertySources(getServletContext(), getServletConfig());
    }

    postProcessWebApplicationContext(wac);
    applyInitializers(wac);
    
    //开始处理bean
    wac.refresh();
}

上面的关键代码都在FrameworkServlet类中，有几个关键点：取除根上下文，创建子上下文并设置父上下文，完成刷新，把子上下文发布到ServletContext中。 到这里可以说子容器（子上下文）已经创建完成。 并把其他初始化web组件的相关工作交给onRefresh方法完成，由DispatcherServlet来重写onRefresh方法，这就又回到了我们熟悉的initStrategies方法。

web组件初始化

@Override
protected void onRefresh(ApplicationContext context) {
    initStrategies(context);
}

protected void initStrategies(ApplicationContext context) {
    //文件上传解析器
    initMultipartResolver(context);
    
    //本地化解析器
    initLocaleResolver(context);
    
    //主题解析器
    initThemeResolver(context);
    
    //处理器映射器(url和Controller方法的映射)
    initHandlerMappings(context);
    
    //处理器适配器(实际执行Controller方法)
    initHandlerAdapters(context);
    
    //处理器异常解析器
    initHandlerExceptionResolvers(context);
    
    //RequestToViewName解析器
    initRequestToViewNameTranslator(context);
    
    //视图解析器(视图的匹配和渲染)
    initViewResolvers(context);
    
    //FlashMap管理者
    initFlashMapManager(context);
}

这里我们主要关注一下三个重要组件：HandlerMapping、HandlerAdapter、ViewResolver。分析这3个组件之前，我们先看一下我们的springMVC-conf.xml配置文件，mvc的配置文件中，我们配置了两行代码：

<context:component-scan base-package="com.zhangfei"/>
<mvc:annotation-driven>

第二行代码主要是添加了默认的HandleMapping,ViewResolver,HandleAdapter。我们看看annotation-driven的源码定义，根据spring自定义schema定义，我们找到如下代码，如图所示：

该文件就一行代码：

http/://www.springframework.org/schema/mvc=org.springframework.web.servlet.config.MvcNamespaceHandler

//MVC所有的标签解析器都定义在此
public class MvcNamespaceHandler extends NamespaceHandlerSupport {
    @Override
    public void init() {
        registerBeanDefinitionParser("annotation-driven", new AnnotationDrivenBeanDefinitionParser());
        registerBeanDefinitionParser("default-servlet-handler", new DefaultServletHandlerBeanDefinitionParser());
        registerBeanDefinitionParser("interceptors", new InterceptorsBeanDefinitionParser());
        registerBeanDefinitionParser("resources", new ResourcesBeanDefinitionParser());
        registerBeanDefinitionParser("view-controller", new ViewControllerBeanDefinitionParser());
        registerBeanDefinitionParser("redirect-view-controller", new ViewControllerBeanDefinitionParser());
        registerBeanDefinitionParser("status-controller", new ViewControllerBeanDefinitionParser());
        registerBeanDefinitionParser("view-resolvers", new ViewResolversBeanDefinitionParser());
        registerBeanDefinitionParser("tiles-configurer", new TilesConfigurerBeanDefinitionParser());
        registerBeanDefinitionParser("freemarker-configurer", new FreeMarkerConfigurerBeanDefinitionParser());
        registerBeanDefinitionParser("groovy-configurer", new GroovyMarkupConfigurerBeanDefinitionParser());
        registerBeanDefinitionParser("script-template-configurer", new ScriptTemplateConfigurerBeanDefinitionParser());
        registerBeanDefinitionParser("cors", new CorsBeanDefinitionParser());
    }
}

那么通过分析AnnotationDrivenBeanDefinitionParser类，主要完成以下三大组件的装配工作：

初始化处理器映射器

private void initHandlerMappings(ApplicationContext context) {
    this.handlerMappings = null;

    //这里detectAllHandlerMappings默认值为true，可以通过配置文件设置为false
    if (this.detectAllHandlerMappings) {
        //从上下文(包含父上下文)中查找所有HandlerMapping实现类
        Map<String, HandlerMapping> matchingBeans =
                BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
        if (!matchingBeans.isEmpty()) {
            this.handlerMappings = new ArrayList<>(matchingBeans.values());
            AnnotationAwareOrderComparator.sort(this.handlerMappings);
        }
    }
    else {
        try {
            //这里只取固定的bean
            HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);
            this.handlerMappings = Collections.singletonList(hm);
        }
        catch (NoSuchBeanDefinitionException ex) {
            
        }
    }
    
    /***
      确保至少有一个HandlerMapping，如果没能找到，注册一个默认的
      默认规则在DispatcherServlet.properties中，这里也就是取BeanNameUrlHandlerMapping、RequestMappingHandlerMapping
    ***/
    if (this.handlerMappings == null) {
        this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);     
    }
}

初始化处理器适配器

private void initHandlerAdapters(ApplicationContext context) {
    this.handlerAdapters = null;

    if (this.detectAllHandlerAdapters) {
        //从上下文（包括父上下文）中查找所有HandlerAdapter实现类
        Map<String, HandlerAdapter> matchingBeans =BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerAdapter.class, true, false);
        if (!matchingBeans.isEmpty()) {
            this.handlerAdapters = new ArrayList<>(matchingBeans.values());
            AnnotationAwareOrderComparator.sort(this.handlerAdapters);
        }
    }
    else {
        try {
            //这里取bean名字为handlerAdapter，类型为HandlerAdapter的处理器适配器
            HandlerAdapter ha = context.getBean(HANDLER_ADAPTER_BEAN_NAME, HandlerAdapter.class);
            this.handlerAdapters = Collections.singletonList(ha);
        }
        catch (NoSuchBeanDefinitionException ex) {
            
        }
    }
    
    /**
    如果没找到，则从默认规则里取出指定的三个实现类：HttpRequestHandlerAdapter、SimpleControllerHandlerAdapter、RequestMappingHandlerAdapter
    **/
    if (this.handlerAdapters == null) {
        this.handlerAdapters = getDefaultStrategies(context, HandlerAdapter.class);     
    }
}

初始化试图解析器

private void initViewResolvers(ApplicationContext context) {
    this.viewResolvers = null;

    if (this.detectAllViewResolvers) {
        //从上下文（包括父上下文）中查找所有ViewResolver实现类
        Map<String, ViewResolver> matchingBeans =BeanFactoryUtils.beansOfTypeIncludingAncestors(context, ViewResolver.class, true, false);
        if (!matchingBeans.isEmpty()) {
            this.viewResolvers = new ArrayList<>(matchingBeans.values());
            AnnotationAwareOrderComparator.sort(this.viewResolvers);
        }
    }
    else {
        try {
            ViewResolver vr = context.getBean(VIEW_RESOLVER_BEAN_NAME, ViewResolver.class);
            this.viewResolvers = Collections.singletonList(vr);
        }
        catch (NoSuchBeanDefinitionException ex) {
            
        }
    }
    
    /**
    如果没找到，则从默认规则里取出指定的实现类：InternalResourceViewResolver
    **/
    if (this.viewResolvers == null) {
        this.viewResolvers = getDefaultStrategies(context, ViewResolver.class); 
    }
}

三大组件的初始化最后判断为NULL时都会调用getDefaultStrategies方法，也就是从DispatcherServlet.properties中取出指定默认值。

protected <T> List<T> getDefaultStrategies(ApplicationContext context, Class<T> strategyInterface) {
    String key = strategyInterface.getName();
    String value = defaultStrategies.getProperty(key);
    if (value != null) {
        String[] classNames = StringUtils.commaDelimitedListToStringArray(value);
        List<T> strategies = new ArrayList<>(classNames.length);
        for (String className : classNames) {
            try {
                Class<?> clazz = ClassUtils.forName(className, DispatcherServlet.class.getClassLoader());
                Object strategy = createDefaultStrategy(context, clazz);
                strategies.add((T) strategy);
            }
            catch (ClassNotFoundException ex) {
                throw new BeanInitializationException("Could not find DispatcherServlet's default strategy class [" + className +"] for interface [" + key + "]", ex);
            }
            catch (LinkageError err) {
                throw new BeanInitializationException("Unresolvable class definition for DispatcherServlet's default strategy class [" +className + "] for interface [" + key + "]", err);
            }
        }
        return strategies;
    }
    else {
        return new LinkedList<>();
    }
}

DispatcherServlet请求处理过程

提到请求处理过程，我们再来回顾一下Servlet生命周期，处理请求都放在service方法中处理，那么也从DispatcherServlet的service方法入手。DispatcherServlet继承FrameworkServlet，在FrameworkServlet中重写了service、doGet、doPost、doPut、doDelete方法。

//FrameworkServlet.java
@Override
protected void service(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    HttpMethod httpMethod = HttpMethod.resolve(request.getMethod());
    if (httpMethod == HttpMethod.PATCH || httpMethod == null) {
        processRequest(request, response);
    }
    else {
        super.service(request, response);
    }
}

    
@Override
protected final void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    processRequest(request, response);
}

    
@Override
protected final void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    processRequest(request, response);
}

    
@Override
protected final void doPut(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    processRequest(request, response);
}

    
@Override
protected final void doDelete(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    processRequest(request, response);
}


protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

    long startTime = System.currentTimeMillis();
    Throwable failureCause = null;

    LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
    LocaleContext localeContext = buildLocaleContext(request);

    RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
    ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);

    WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
    asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());
    
    //把新构造的LocaleContext对象和ServletRequestAttributes对象和当前请求线程绑定（后面要解除绑定）
    initContextHolders(request, localeContext, requestAttributes);

    try {
        //抽象方法，交给DispatcherServlet方法实现
        doService(request, response);
    }
    catch (ServletException | IOException ex) {
        failureCause = ex;
        throw ex;
    }
    catch (Throwable ex) {
        failureCause = ex;
        throw new NestedServletException("Request processing failed", ex);
    }

    finally {
        //重置LocaleContext和RequestAttributes对象，也就是解除LocaleContext对象和ServletRequestAttributes对象和当前请求线程的绑定
        resetContextHolders(request, previousLocaleContext, previousAttributes);
        if (requestAttributes != null) {
            requestAttributes.requestCompleted();
        }
        //发布ServletRequestHandledEvent事件
        publishRequestHandledEvent(request, response, startTime, failureCause);
    }
}

//DispatcherServlet.java
@Override
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
    
    Map<String, Object> attributesSnapshot = null;
    if (WebUtils.isIncludeRequest(request)) {
        attributesSnapshot = new HashMap<>();
        Enumeration<?> attrNames = request.getAttributeNames();
        while (attrNames.hasMoreElements()) {
            String attrName = (String) attrNames.nextElement();
            if (this.cleanupAfterInclude || attrName.startsWith(DEFAULT_STRATEGIES_PREFIX)) {
                attributesSnapshot.put(attrName, request.getAttribute(attrName));
            }
        }
    }
    
    //在当前request对象中填充4个属性
    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());

    if (this.flashMapManager != null) {
        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 {
        //主要处理分发请求
        doDispatch(request, response);
    }
    finally {
        if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
            if (attributesSnapshot != null) {
                restoreAttributesAfterInclude(request, attributesSnapshot);
            }
        }
    }
}


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);
            
            //调用handlerMapping获取handlerChain
            mappedHandler = getHandler(processedRequest);
            if (mappedHandler == null) {
                noHandlerFound(processedRequest, response);
                return;
            }

            //获取支持该handler解析的HandlerAdapter
            HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

            String method = request.getMethod();
            boolean isGet = "GET".equals(method);
            if (isGet || "HEAD".equals(method)) {
                long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
                if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
                    return;
                }
            }

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

            //使用HandlerAdapter完成handler处理
            mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

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

            //视图处理(页面渲染)
            applyDefaultViewName(processedRequest, mv);
            mappedHandler.applyPostHandle(processedRequest, response, mv);
        }
        catch (Exception ex) {
            dispatchException = ex;
        }
        catch (Throwable err) {
            dispatchException = new NestedServletException("Handler dispatch failed", err);
        }
        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()) {
            if (mappedHandler != null) {
                mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
            }
        }
        else {
            if (multipartRequestParsed) {
                cleanupMultipart(processedRequest);
            }
        }
    }
}

DispatcherServlet的doDispatch方法概括起来大致就是以下几点：首先根据当前请求路径找到对应的HandlerMethod，一个HandlerMethod和若干个拦截器构造一个 HandlerExecutionChain. 通过 HandlerExecutionChain 得到 HandlerAdapter 对象 ， 通过执行 HandlerAdapter 的handle方法得到 ModelAndView 对象，调用ModelAndView解析视图，渲染视图，Response结束。

参考