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Spring 框架 - DispatcherServlet实现

# Spring 框架 - DispatcherServlet实现

# DispatcherServlet初始化过程

# DispatcherServlet和ApplicationContext有何关系？

DispatcherServlet 作为一个 Servlet，需要根据 Servlet 规范使用 Java 配置或 web.xml 声明和映射。反过来，DispatcherServlet 使用 Spring 配置来发现请求映射、视图解析、异常处理等等所需的委托组件。那它和ApplicationContext有和关系呢？如下内容可以参考官网-SpringMVC文档 (opens new window)

DispatcherServlet 需要 WebApplicationContext（继承自 ApplicationContext） 来配置。WebApplicationContext 可以链接到ServletContext 和 Servlet。因为绑定了 ServletContext，这样应用程序就可以在需要的时候使用 RequestContextUtils 的静态方法访问 WebApplicationContext。

大多数应用程序只有一个WebApplicationContext，除此之外也可以一个Root WebApplicationContext 被多个 Servlet实例，然后各自拥有自己的Servlet WebApplicationContext 配置。

Root WebApplicationContext 包含需要共享给多个 Servlet 实例的数据源和业务服务基础 Bean。这些 Bean 可以在 Servlet 特定的范围被继承或覆盖。

（PS：官网上的这张图可以可以帮助你构建DispatcherServlet和ApplicationContext在设计上的认知，这一点对于理解DispatcherServlet的设计和初始化过程非常重要）

img

# DispatcherServlet如何初始化？

DispatcherServlet首先是Sevlet，Servlet有自己的生命周期的方法（init,destory等），那么我们在看DispatcherServlet初始化时首先需要看源码中DispatcherServlet的类结构设计。

首先我们看DispatcherServlet的类结构关系，在这个类依赖结构中找到init的方法

img

很容易找到init()的方法位于HttpServletBean中，然后跑Spring基础 - SpringMVC请求流程和案例中的代码，在init方法中打断点。

img

# init

init()方法如下, 主要读取web.xml中servlet参数配置，并将交给子类方法initServletBean()继续初始化

/**
  * Map config parameters onto bean properties of this servlet, and
  * invoke subclass initialization.
  * @throws ServletException if bean properties are invalid (or required
  * properties are missing), or if subclass initialization fails.
  */
@Override
public final void init() throws ServletException {

  // 读取web.xml中的servlet配置
  PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
  if (!pvs.isEmpty()) {
    try {
      // 转换成BeanWrapper，为了方便使用Spring的属性注入功能
      BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
      // 注入Resource类型需要依赖于ResourceEditor解析，所以注册Resource类关联到ResourceEditor解析器
      ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
      bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
      // 更多的初始化可以让子类去拓展
      initBeanWrapper(bw);
      // 让spring注入namespace,contextConfigLocation等属性
      bw.setPropertyValues(pvs, true);
    }
    catch (BeansException ex) {
      if (logger.isErrorEnabled()) {
        logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
      }
      throw ex;
    }
  }

  // 让子类去拓展
  initServletBean();
}
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读取配置可以从下图看出，正是初始化了我们web.xml中配置

img

再看下initServletBean()方法，位于FrameworkServlet类中

/**
  * Overridden method of {@link HttpServletBean}, invoked after any bean properties
  * have been set. Creates this servlet's WebApplicationContext.
  */
@Override
protected final void initServletBean() throws ServletException {
  getServletContext().log("Initializing Spring " + getClass().getSimpleName() + " '" + getServletName() + "'");
  if (logger.isInfoEnabled()) {
    logger.info("Initializing Servlet '" + getServletName() + "'");
  }
  long startTime = System.currentTimeMillis();

  try {
    // 最重要的是这个方法
    this.webApplicationContext = initWebApplicationContext();

    // 可以让子类进一步拓展
    initFrameworkServlet();
  }
  catch (ServletException | RuntimeException ex) {
    logger.error("Context initialization failed", ex);
    throw ex;
  }

  if (logger.isDebugEnabled()) {
    String value = this.enableLoggingRequestDetails ?
        "shown which may lead to unsafe logging of potentially sensitive data" :
        "masked to prevent unsafe logging of potentially sensitive data";
    logger.debug("enableLoggingRequestDetails='" + this.enableLoggingRequestDetails +
        "': request parameters and headers will be " + value);
  }

  if (logger.isInfoEnabled()) {
    logger.info("Completed initialization in " + (System.currentTimeMillis() - startTime) + " ms");
  }
}
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# initWebApplicationContext

initWebApplicationContext用来初始化和刷新WebApplicationContext。

initWebApplicationContext() 方法如下

/**
  * Initialize and publish the WebApplicationContext for this servlet.
  * <p>Delegates to {@link #createWebApplicationContext} for actual creation
  * of the context. Can be overridden in subclasses.
  * @return the WebApplicationContext instance
  * @see #FrameworkServlet(WebApplicationContext)
  * @see #setContextClass
  * @see #setContextConfigLocation
  */
protected WebApplicationContext initWebApplicationContext() {
  WebApplicationContext rootContext =
      WebApplicationContextUtils.getWebApplicationContext(getServletContext());
  WebApplicationContext wac = null;

  // 如果在构造函数已经被初始化
  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);
      }
    }
  }
  // 没有在构造函数中初始化，则尝试通过contextAttribute初始化
  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();
  }

  // 还没有的话，只能重新创建了
  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.
    synchronized (this.onRefreshMonitor) {
      onRefresh(wac);
    }
  }

  if (this.publishContext) {
    // Publish the context as a servlet context attribute.
    String attrName = getServletContextAttributeName();
    getServletContext().setAttribute(attrName, wac);
  }

  return wac;
}
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webApplicationContext只会初始化一次，依次尝试构造函数初始化，没有则通过contextAttribute初始化，仍没有则创建新的

创建的createWebApplicationContext方法如下

/**
  * Instantiate the WebApplicationContext for this servlet, either a default
  * {@link org.springframework.web.context.support.XmlWebApplicationContext}
  * or a {@link #setContextClass custom context class}, if set.
  * <p>This implementation expects custom contexts to implement the
  * {@link org.springframework.web.context.ConfigurableWebApplicationContext}
  * interface. Can be overridden in subclasses.
  * <p>Do not forget to register this servlet instance as application listener on the
  * created context (for triggering its {@link #onRefresh callback}, and to call
  * {@link org.springframework.context.ConfigurableApplicationContext#refresh()}
  * before returning the context instance.
  * @param parent the parent ApplicationContext to use, or {@code null} if none
  * @return the WebApplicationContext for this servlet
  * @see org.springframework.web.context.support.XmlWebApplicationContext
  */
protected WebApplicationContext createWebApplicationContext(@Nullable ApplicationContext parent) {
  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");
  }

  // 通过反射方式初始化
  ConfigurableWebApplicationContext wac =
      (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);

  wac.setEnvironment(getEnvironment());
  wac.setParent(parent);
  String configLocation = getContextConfigLocation(); // 就是前面Demo中的springmvc.xml
  if (configLocation != null) {
    wac.setConfigLocation(configLocation);
  }

  // 初始化Spring环境
  configureAndRefreshWebApplicationContext(wac);

  return wac;
}
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configureAndRefreshWebApplicationContext方法初始化设置Spring环境

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {
  // 设置context 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());
    }
  }

  // 设置servletContext, servletConfig, namespace, listener...
  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());
  }

  // 让子类去拓展
  postProcessWebApplicationContext(wac);
  applyInitializers(wac);

  // Spring环境初始化完了，就可以初始化DispatcherServlet处理流程中需要的组件了。
  wac.refresh();
}
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# refresh

有了webApplicationContext后，就开始刷新了（onRefresh()方法），这个方法是FrameworkServlet提供的模板方法，由子类DispatcherServlet来实现的。

/**
  * This implementation calls {@link #initStrategies}.
  */
@Override
protected void onRefresh(ApplicationContext context) {
  initStrategies(context);
}
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刷新主要是调用initStrategies(context)方法对DispatcherServlet中的组件进行初始化，这些组件就是在SpringMVC请求流程中包的主要组件。

/**
  * Initialize the strategy objects that this servlet uses.
  * <p>May be overridden in subclasses in order to initialize further strategy objects.
  */
protected void initStrategies(ApplicationContext context) {
  initMultipartResolver(context);
  initLocaleResolver(context);
  initThemeResolver(context);

  // 主要看如下三个方法
  initHandlerMappings(context);
  initHandlerAdapters(context);
  initHandlerExceptionResolvers(context);

  initRequestToViewNameTranslator(context);
  initViewResolvers(context);
  initFlashMapManager(context);
}
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# initHanlderxxx

我们主要看initHandlerXXX相关的方法，它们之间的关系可以看SpringMVC的请求流程：

img

  1. HandlerMapping是映射处理器
  2. HandlerAdpter是处理适配器，它用来找到你的Controller中的处理方法
  3. HandlerExceptionResolver是当遇到处理异常时的异常解析器

initHandlerMapping方法如下，无非就是获取按照优先级排序后的HanlderMappings, 将来匹配时按照优先级最高的HanderMapping进行处理。

img

initHandlerAdapters方法和initHandlerExceptionResolvers方法也是类似的，如果没有找到，那就构建默认的。

/**
  * Initialize the HandlerAdapters used by this class.
  * <p>If no HandlerAdapter beans are defined in the BeanFactory for this namespace,
  * we default to SimpleControllerHandlerAdapter.
  */
private void initHandlerAdapters(ApplicationContext context) {
  this.handlerAdapters = null;

  if (this.detectAllHandlerAdapters) {
    // Find all HandlerAdapters in the ApplicationContext, including ancestor contexts.
    Map<String, HandlerAdapter> matchingBeans =
        BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerAdapter.class, true, false);
    if (!matchingBeans.isEmpty()) {
      this.handlerAdapters = new ArrayList<>(matchingBeans.values());
      // We keep HandlerAdapters in sorted order.
      AnnotationAwareOrderComparator.sort(this.handlerAdapters);
    }
  }
  else {
    try {
      HandlerAdapter ha = context.getBean(HANDLER_ADAPTER_BEAN_NAME, HandlerAdapter.class);
      this.handlerAdapters = Collections.singletonList(ha);
    }
    catch (NoSuchBeanDefinitionException ex) {
      // Ignore, we'll add a default HandlerAdapter later.
    }
  }

  // Ensure we have at least some HandlerAdapters, by registering
  // default HandlerAdapters if no other adapters are found.
  if (this.handlerAdapters == null) {
    this.handlerAdapters = getDefaultStrategies(context, HandlerAdapter.class);
    if (logger.isTraceEnabled()) {
      logger.trace("No HandlerAdapters declared for servlet '" + getServletName() +
          "': using default strategies from DispatcherServlet.properties");
    }
  }
}

/**
  * Initialize the HandlerExceptionResolver used by this class.
  * <p>If no bean is defined with the given name in the BeanFactory for this namespace,
  * we default to no exception resolver.
  */
private void initHandlerExceptionResolvers(ApplicationContext context) {
  this.handlerExceptionResolvers = null;

  if (this.detectAllHandlerExceptionResolvers) {
    // Find all HandlerExceptionResolvers in the ApplicationContext, including ancestor contexts.
    Map<String, HandlerExceptionResolver> matchingBeans = BeanFactoryUtils
        .beansOfTypeIncludingAncestors(context, HandlerExceptionResolver.class, true, false);
    if (!matchingBeans.isEmpty()) {
      this.handlerExceptionResolvers = new ArrayList<>(matchingBeans.values());
      // We keep HandlerExceptionResolvers in sorted order.
      AnnotationAwareOrderComparator.sort(this.handlerExceptionResolvers);
    }
  }
  else {
    try {
      HandlerExceptionResolver her =
          context.getBean(HANDLER_EXCEPTION_RESOLVER_BEAN_NAME, HandlerExceptionResolver.class);
      this.handlerExceptionResolvers = Collections.singletonList(her);
    }
    catch (NoSuchBeanDefinitionException ex) {
      // Ignore, no HandlerExceptionResolver is fine too.
    }
  }

  // Ensure we have at least some HandlerExceptionResolvers, by registering
  // default HandlerExceptionResolvers if no other resolvers are found.
  if (this.handlerExceptionResolvers == null) {
    this.handlerExceptionResolvers = getDefaultStrategies(context, HandlerExceptionResolver.class);
    if (logger.isTraceEnabled()) {
      logger.trace("No HandlerExceptionResolvers declared in servlet '" + getServletName() +
          "': using default strategies from DispatcherServlet.properties");
    }
  }
}
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最后我们看下初始化的日志：

21:30:33.163 [RMI TCP Connection(2)-127.0.0.1] INFO org.springframework.web.servlet.DispatcherServlet - Initializing Servlet 'springmvc-demo'
21:30:38.242 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.web.context.support.XmlWebApplicationContext - Refreshing WebApplicationContext for namespace 'springmvc-demo-servlet'
21:30:39.256 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.context.annotation.ClassPathBeanDefinitionScanner - Identified candidate component class: file [/Users/pdai/pdai/www/tech-pdai-spring-demos/011-spring-framework-demo-springmvc/target/011-spring-framework-demo-springmvc-1.0-SNAPSHOT/WEB-INF/classes/tech/pdai/springframework/springmvc/controller/UserController.class]
21:30:39.261 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.context.annotation.ClassPathBeanDefinitionScanner - Identified candidate component class: file [/Users/pdai/pdai/www/tech-pdai-spring-demos/011-spring-framework-demo-springmvc/target/011-spring-framework-demo-springmvc-1.0-SNAPSHOT/WEB-INF/classes/tech/pdai/springframework/springmvc/dao/UserDaoImpl.class]
21:30:39.274 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.context.annotation.ClassPathBeanDefinitionScanner - Identified candidate component class: file [/Users/pdai/pdai/www/tech-pdai-spring-demos/011-spring-framework-demo-springmvc/target/011-spring-framework-demo-springmvc-1.0-SNAPSHOT/WEB-INF/classes/tech/pdai/springframework/springmvc/service/UserServiceImpl.class]
21:30:39.546 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.xml.XmlBeanDefinitionReader - Loaded 29 bean definitions from class path resource [springmvc.xml]
21:30:39.711 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalConfigurationAnnotationProcessor'
21:30:39.973 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.event.internalEventListenerProcessor'
21:30:39.984 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.event.internalEventListenerFactory'
21:30:39.995 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalAutowiredAnnotationProcessor'
21:30:40.003 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalCommonAnnotationProcessor'
21:30:40.042 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.ui.context.support.UiApplicationContextUtils - Unable to locate ThemeSource with name 'themeSource': using default [org.springframework.ui.context.support.ResourceBundleThemeSource@791af912]
21:30:40.052 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'userController'
21:30:40.136 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'userServiceImpl'
21:30:40.140 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'userDaoImpl'
21:30:40.147 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.resource.DefaultServletHttpRequestHandler#0'
21:30:40.153 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.handler.SimpleUrlHandlerMapping#0'
21:30:40.350 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.handler.MappedInterceptor#0'
21:30:40.356 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.format.support.FormattingConversionServiceFactoryBean#0'
21:30:40.741 [RMI TCP Connection(2)-127.0.0.1] DEBUG _org.springframework.web.servlet.HandlerMapping.Mappings - 'org.springframework.web.servlet.handler.SimpleUrlHandlerMapping#0' {/**=org.springframework.web.servlet.resource.DefaultServletHttpRequestHandler@216c0f1f}
21:30:40.742 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'mvcCorsConfigurations'
21:30:40.742 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping'
21:30:40.792 [RMI TCP Connection(2)-127.0.0.1] DEBUG _org.springframework.web.servlet.HandlerMapping.Mappings - 'org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping' {}
21:30:40.792 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter'
21:30:40.793 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter'
21:30:40.794 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'localeResolver'
21:30:40.796 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'themeResolver'
21:30:40.798 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'viewNameTranslator'
21:30:40.799 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'flashMapManager'
21:30:40.805 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'mvcContentNegotiationManager'
21:30:40.887 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping'
21:30:41.150 [RMI TCP Connection(2)-127.0.0.1] DEBUG _org.springframework.web.servlet.HandlerMapping.Mappings - 
	t.p.s.s.c.UserController:
	{ [/user]}: list(HttpServletRequest,HttpServletResponse)
21:30:41.202 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping - 1 mappings in 'org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping'
21:30:41.202 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter'
21:30:41.626 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter - ControllerAdvice beans: none
21:30:41.738 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'mvcUriComponentsContributor'
21:30:41.786 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter - ControllerAdvice beans: none
21:30:41.806 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver#0'
21:30:41.919 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver - ControllerAdvice beans: none
21:30:41.920 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver#0'
21:30:41.949 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver#0'
21:30:41.967 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'jspViewResolver'
21:30:44.214 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.web.servlet.DispatcherServlet - Detected AcceptHeaderLocaleResolver
21:30:44.214 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.web.servlet.DispatcherServlet - Detected FixedThemeResolver
21:31:02.141 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.web.servlet.DispatcherServlet - Detected org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator@d57bc91
21:31:03.483 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.web.servlet.DispatcherServlet - Detected org.springframework.web.servlet.support.SessionFlashMapManager@2b4e795e
21:44:08.180 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.jndi.JndiTemplate - Looking up JNDI object with name [java:comp/env/spring.liveBeansView.mbeanDomain]
21:44:08.185 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.jndi.JndiLocatorDelegate - Converted JNDI name [java:comp/env/spring.liveBeansView.mbeanDomain] not found - trying original name [spring.liveBeansView.mbeanDomain]. javax.naming.NameNotFoundException: 名称[spring.liveBeansView.mbeanDomain]未在此上下文中绑定。找不到[spring.liveBeansView.mbeanDomain]。
21:44:08.185 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.jndi.JndiTemplate - Looking up JNDI object with name [spring.liveBeansView.mbeanDomain]
21:44:08.185 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.jndi.JndiPropertySource - JNDI lookup for name [spring.liveBeansView.mbeanDomain] threw NamingException with message: 名称[spring.liveBeansView.mbeanDomain]未在此上下文中绑定。找不到[spring.liveBeansView.mbeanDomain]。. Returning null.
21:44:08.195 [RMI TCP Connection(2)-127.0.0.1] DEBUG org.springframework.web.servlet.DispatcherServlet - enableLoggingRequestDetails='false': request parameters and headers will be masked to prevent unsafe logging of potentially sensitive data
21:44:08.195 [RMI TCP Connection(2)-127.0.0.1] INFO org.springframework.web.servlet.DispatcherServlet - Completed initialization in 815032 ms
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# DispatcherServlet处理请求的过程？

一个请求发出，经过DispatcherServlet进行了什么样的处理，最后将内容返回的呢？

# 回顾整理处理流程

首先让我们整体看一下Spring Web MVC 处理请求的流程：

img

核心架构的具体流程步骤如下：

  1. 首先用户发送请求——>DispatcherServlet，前端控制器收到请求后自己不进行处理，而是委托给其他的解析器进行 处理，作为统一访问点，进行全局的流程控制；
  2. DispatcherServlet——>HandlerMapping， HandlerMapping 将会把请求映射为 HandlerExecutionChain 对象（包含一 个Handler 处理器（页面控制器）对象、多个HandlerInterceptor 拦截器）对象，通过这种策略模式，很容易添加新 的映射策略；
  3. DispatcherServlet——>HandlerAdapter，HandlerAdapter 将会把处理器包装为适配器，从而支持多种类型的处理器， 即适配器设计模式的应用，从而很容易支持很多类型的处理器；
  4. HandlerAdapter——>处理器功能处理方法的调用，HandlerAdapter 将会根据适配的结果调用真正的处理器的功能处 理方法，完成功能处理；并返回一个ModelAndView 对象（包含模型数据、逻辑视图名）；
  5. ModelAndView 的逻辑视图名——> ViewResolver，ViewResolver 将把逻辑视图名解析为具体的View，通过这种策 略模式，很容易更换其他视图技术；
  6. View——>渲染，View 会根据传进来的Model 模型数据进行渲染，此处的Model 实际是一个Map 数据结构，因此 很容易支持其他视图技术；
  7. 返回控制权给DispatcherServlet，由DispatcherServlet 返回响应给用户，到此一个流程结束。

# doGet入口

我们以上个demo中这个GET请求为例，请求URL是http://localhost:8080/011_spring_framework_demo_springmvc_war_exploded/user

我们知道servlet处理get请求是doGet方法，所以我们去找DispatcherServlet类结构中的doGet方法。

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

  processRequest(request, response);
}
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processRequest处理请求的方法如下：

/**
  * Process this request, publishing an event regardless of the outcome.
  * <p>The actual event handling is performed by the abstract
  * {@link #doService} template method.
  */
protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {

  // 计算处理请求的时间
  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());

  // 初始化context
  initContextHolders(request, localeContext, requestAttributes);

  try {
    // 看这里
    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context
    resetContextHolders(request, previousLocaleContext, previousAttributes);
    if (requestAttributes != null) {
      requestAttributes.requestCompleted();
    }
    logResult(request, response, failureCause, asyncManager);
    publishRequestHandledEvent(request, response, startTime, failureCause);
  }
}
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本质上就是调用doService方法，由DispatchServlet类实现

/**
  * Exposes the DispatcherServlet-specific request attributes and delegates to {@link #doDispatch}
  * for the actual dispatching.
  */
@Override
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
  logRequest(request);

  // 保存下请求之前的参数.
  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));
      }
    }
  }

  // 方便后续 handlers 和 view 要使用它们.
  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);
  }

  RequestPath previousRequestPath = null;
  if (this.parseRequestPath) {
    previousRequestPath = (RequestPath) request.getAttribute(ServletRequestPathUtils.PATH_ATTRIBUTE);
    ServletRequestPathUtils.parseAndCache(request);
  }

  try {
    // 看这里，终于将这个请求分发出去了
    doDispatch(request, response);
  }
  finally {
    if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
      // Restore the original attribute snapshot, in case of an include.
      if (attributesSnapshot != null) {
        restoreAttributesAfterInclude(request, attributesSnapshot);
      }
    }
    if (this.parseRequestPath) {
      ServletRequestPathUtils.setParsedRequestPath(previousRequestPath, request);
    }
  }
}
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# 请求分发

doDispatch方法是真正处理请求的核心方法

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 {
      // 判断是不是文件上传类型的request
      processedRequest = checkMultipart(request);
      multipartRequestParsed = (processedRequest != request);

      // 根据request获取匹配的handler.
      mappedHandler = getHandler(processedRequest);
      if (mappedHandler == null) {
        noHandlerFound(processedRequest, response);
        return;
      }

      // 根据handler获取匹配的handlerAdapter
      HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

      // 如果handler支持last-modified头处理
      String method = request.getMethod();
      boolean isGet = HttpMethod.GET.matches(method);
      if (isGet || HttpMethod.HEAD.matches(method)) {
        long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
        if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
          return;
        }
      }

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

      // 真正handle处理，并返回modelAndView
      mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

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

      // 通过视图的prefix和postfix获取完整的视图名
      applyDefaultViewName(processedRequest, mv);

      // 应用后置的拦截器
      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);
    }

    // 处理handler处理的结果，显然就是对ModelAndView 或者 出现的Excpetion处理
    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.
      if (multipartRequestParsed) {
        cleanupMultipart(processedRequest);
      }
    }
  }
}
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# 映射和适配器处理

对于真正的handle方法，我们看下其处理流程

/**
  * This implementation expects the handler to be an {@link HandlerMethod}.
  */
@Override
@Nullable
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
    throws Exception {

  return handleInternal(request, response, (HandlerMethod) handler);
}
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交给handleInternal方法处理，以RequestMappingHandlerAdapter这个HandlerAdapter中的处理方法为例

@Override
protected ModelAndView handleInternal(HttpServletRequest request,
    HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

  ModelAndView mav;
  checkRequest(request);

  // Execute invokeHandlerMethod in synchronized block if required.
  if (this.synchronizeOnSession) {
    HttpSession session = request.getSession(false);
    if (session != null) {
      Object mutex = WebUtils.getSessionMutex(session);
      synchronized (mutex) {
        mav = invokeHandlerMethod(request, response, handlerMethod);
      }
    }
    else {
      // No HttpSession available -> no mutex necessary
      mav = invokeHandlerMethod(request, response, handlerMethod);
    }
  }
  else {
    // No synchronization on session demanded at all...
    mav = invokeHandlerMethod(request, response, handlerMethod);
  }

  if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
    if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
      applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
    }
    else {
      prepareResponse(response);
    }
  }

  return mav;
}
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img

然后执行invokeHandlerMethod这个方法，用来对RequestMapping（usercontroller中的list方法）进行处理

/**
  * Invoke the {@link RequestMapping} handler method preparing a {@link ModelAndView}
  * if view resolution is required.
  * @since 4.2
  * @see #createInvocableHandlerMethod(HandlerMethod)
  */
@Nullable
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
    HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

  ServletWebRequest webRequest = new ServletWebRequest(request, response);
  try {
    
    WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
    ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);

    // 重要：设置handler(controller#list)方法上的参数，返回值处理，绑定databinder等
    ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
    if (this.argumentResolvers != null) {
      invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
    }
    if (this.returnValueHandlers != null) {
      invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
    }
    invocableMethod.setDataBinderFactory(binderFactory);
    invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);

    ModelAndViewContainer mavContainer = new ModelAndViewContainer();
    mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
    modelFactory.initModel(webRequest, mavContainer, invocableMethod);
    mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);

    
    AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
    asyncWebRequest.setTimeout(this.asyncRequestTimeout);

    WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
    asyncManager.setTaskExecutor(this.taskExecutor);
    asyncManager.setAsyncWebRequest(asyncWebRequest);
    asyncManager.registerCallableInterceptors(this.callableInterceptors);
    asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);

    if (asyncManager.hasConcurrentResult()) {
      Object result = asyncManager.getConcurrentResult();
      mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];
      asyncManager.clearConcurrentResult();
      LogFormatUtils.traceDebug(logger, traceOn -> {
        String formatted = LogFormatUtils.formatValue(result, !traceOn);
        return "Resume with async result [" + formatted + "]";
      });
      invocableMethod = invocableMethod.wrapConcurrentResult(result);
    }

    // 执行controller中方法
    invocableMethod.invokeAndHandle(webRequest, mavContainer);
    if (asyncManager.isConcurrentHandlingStarted()) {
      return null;
    }

    return getModelAndView(mavContainer, modelFactory, webRequest);
  }
  finally {
    webRequest.requestCompleted();
  }
}
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invokeAndHandle交给UserController中具体执行list方法执行

img

后续invoke执行的方法，直接看整个请求流程的调用链即可

img

执行后获得视图和Model

img

# 视图渲染

接下来继续执行processDispatchResult方法，对视图和model（如果有异常则对异常处理）进行处理（显然就是渲染页面了）

/**
  * Handle the result of handler selection and handler invocation, which is
  * either a ModelAndView or an Exception to be resolved to a ModelAndView.
  */
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
    @Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
    @Nullable Exception exception) throws Exception {

  boolean errorView = false;

  // 如果处理过程有异常，则异常处理
  if (exception != null) {
    if (exception instanceof ModelAndViewDefiningException) {
      logger.debug("ModelAndViewDefiningException encountered", exception);
      mv = ((ModelAndViewDefiningException) exception).getModelAndView();
    }
    else {
      Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
      mv = processHandlerException(request, response, handler, exception);
      errorView = (mv != null);
    }
  }

  // 是否需要渲染视图
  if (mv != null && !mv.wasCleared()) {
    render(mv, request, response); // 渲染视图
    if (errorView) {
      WebUtils.clearErrorRequestAttributes(request);
    }
  }
  else {
    if (logger.isTraceEnabled()) {
      logger.trace("No view rendering, null ModelAndView returned.");
    }
  }

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

  if (mappedHandler != null) {
    // Exception (if any) is already handled..
    mappedHandler.triggerAfterCompletion(request, response, null);
  }
}
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接下来显然就是渲染视图了, spring在initStrategies方法中初始化的组件（LocaleResovler等）就派上用场了。

/**
  * 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 != null ? this.localeResolver.resolveLocale(request) : request.getLocale());
  response.setLocale(locale);

  View view;
  String viewName = mv.getViewName();
  if (viewName != null) {
    // We need to resolve the view name.
    view = resolveViewName(viewName, 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.isTraceEnabled()) {
    logger.trace("Rendering view [" + view + "] ");
  }
  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 + "]", ex);
    }
    throw ex;
  }
}
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后续就是通过viewResolver进行解析了，这里就不再继续看代码了，上述流程基本上够帮助你构建相关的认知了。

最后无非是返回控制权给DispatcherServlet，由DispatcherServlet 返回响应给用户。

最后的最后我们看下请求的日志：

21:45:53.390 [http-nio-8080-exec-6] DEBUG org.springframework.web.servlet.DispatcherServlet - GET "/011_spring_framework_demo_springmvc_war_exploded/user", parameters={}
21:45:53.400 [http-nio-8080-exec-6] DEBUG org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping - Mapped to tech.pdai.springframework.springmvc.controller.UserController#list(HttpServletRequest, HttpServletResponse)
22:51:14.504 [http-nio-8080-exec-6] DEBUG org.springframework.web.servlet.view.JstlView - View name 'userList', model {dateTime=Fri Apr 22 21:45:53 CST 2022, userList=[tech.pdai.springframework.springmvc.entity.User@7b8c8dc]}
22:51:14.550 [http-nio-8080-exec-6] DEBUG org.springframework.web.servlet.view.JstlView - Forwarding to [/WEB-INF/views/userList.jsp]
22:51:44.395 [http-nio-8080-exec-6] DEBUG org.springframework.web.servlet.DispatcherServlet - Completed 200 OK
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著作权归@pdai所有 原文链接：

  • https://pdai.tech/md/spring/spring-x-framework-springmvc-source-1.html
  • https://pdai.tech/md/spring/spring-x-framework-springmvc-source-2.html
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上次更新: 2024-08-19
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