从可以看到,启动上下文之后，紧接着就开始初始化servlet,调用init方法

private synchronized void initServlet()        throws ServletException    {        ...        //调用Servlet的init方法        _servlet.init(_config);        ...    }复制代码

从web.xml文件中可以看到，这个servlet就是DispatcherServlet,对应的init方法在父类GenericServlet中

public void init(ServletConfig config) throws ServletException {//这里servletconfig就被传下来this.config = config;//执行子类的init方法this.init();}复制代码

对应在 HttpServletBean中

public final void init() throws ServletException {    ...    initServletBean();}复制代码

在FrameworkServlet中实现对应的spring的servlet的初始化

protected final void initServletBean() throws ServletException {…this.webApplicationContext = initWebApplicationContext();…}复制代码

对应的初始化web容器，首先也会去查询是否已经初始化过了

protected WebApplicationContext initWebApplicationContext() {    //获取根webapplicationcontext，这就是在IOC容器初始化的时候塞入的值，如果IoC容器已经初始化完成，那么这里的值肯定不是null   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()) {       //如果没有执行过webcontextapplication的refresh,那么再执行一次    if (cwac.getParent() == null) {         cwac.setParent(rootContext);      }      //这个过程就类似IOC的启动了      configureAndRefreshWebApplicationContext(cwac);   }}   }   ...   if (!this.refreshEventReceived) {      //没有执行过refresh则执行一次      onRefresh(wac);   }    ….   return wac;}复制代码

对于这个时间点的DispatcherServlet启动来说，核心在于 onRefresh,它会去初始化各种resolver

protected void onRefresh(ApplicationContext context) { …initMultipartResolver(context);...initHandlerMappings(context);...initViewResolvers(context); …}复制代码

MultipartResolver

它会从容器中读取是否包含 bean ‘multipartResolver'

public static final String MULTIPART_RESOLVER_BEAN_NAME = "multipartResolver”;...private void initMultipartResolver(ApplicationContext context) {      ...      this.multipartResolver = context.getBean(MULTIPART_RESOLVER_BEAN_NAME, MultipartResolver.class);      ...}复制代码

MultipartResolver是用来解决文件上传问题

HandlerMappings

默认自己去扫描所有HandlerMapping类型的

private void initHandlerMappings(ApplicationContext context) {   this.handlerMappings = null;   if (this.detectAllHandlerMappings) {    //默认这里执行主动探测，这里的实现其实就是从BeanFactory中获取所有已经注册了的，且类型是HandlerMapping的类的名字，然后再从BeanFactory中获取所有这个名字的bean作为返回      Map
    
      matchingBeans =            BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);      if (!matchingBeans.isEmpty()) {         this.handlerMappings = new ArrayList<>(matchingBeans.values());            AnnotationAwareOrderComparator.sort(this.handlerMappings);      }   }   ...  if (this.handlerMappings == null) {      //没有handlerMapping，则使用默认的。      this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);      if (logger.isTraceEnabled()) {         logger.trace("No HandlerMappings declared for servlet '" + getServletName() +               "': using default strategies from DispatcherServlet.properties");      }   }}复制代码
    

在没有配置的情况下，处理映射的类配置在spring自带的文件DispatcherServlet.properties中，默认handlerMapping的类为

org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\   org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping复制代码

HandlerMapping负责定义请求和处理请求的对象之间的映射

以RequestMappingHandlerMapping为例。当获取到对应的名字后

protected 
    
      List
     
       getDefaultStrategies(ApplicationContext context, Class
      
        strategyInterface) {   String key = strategyInterface.getName();  //获取默认的配置   String value = defaultStrategies.getProperty(key);     ….    //通过反射构建class对象            Class
        clazz = ClassUtils.forName(className, DispatcherServlet.class.getClassLoader());    //从beanFactory中获取对象，其实就是调用createBean方法            Object strategy = createDefaultStrategy(context, clazz);            strategies.add((T) strategy);         }        ….}复制代码
      
     
    

对于beanFactory来说，创建一个bean或经历它的完整生命周期，经过多层查找，可以看到如下代码

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)      throws BeanCreationException {    BeanWrapper instanceWrapper = null;   ...      instanceWrapper = createBeanInstance(beanName, mbd, args);   ...   final Object bean = instanceWrapper.getWrappedInstance();...  Object exposedObject = bean;...      exposedObject = initializeBean(beanName, exposedObject, mbd);...}复制代码

执行一些列的生命名周期方法

protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {   ...   //执行各种aware方法      invokeAwareMethods(beanName, bean);   …    //执行初始化之前的BeanPostProcessor相关方法      wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);      …   //执行初始化bean方法      invokeInitMethods(beanName, wrappedBean, mbd);    …    //执行初始化之后的BeanPostProcessor相关方法      wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);   ...}复制代码

-aware 方法

private void invokeAwareMethods(final String beanName, final Object bean) {  if (bean instanceof Aware) {     if (bean instanceof BeanNameAware) {        ((BeanNameAware) bean).setBeanName(beanName);     }     if (bean instanceof BeanClassLoaderAware) {        ClassLoader bcl = getBeanClassLoader();        if (bcl != null) {           ((BeanClassLoaderAware) bean).setBeanClassLoader(bcl);        }     }     if (bean instanceof BeanFactoryAware) {        ((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);     }  }}复制代码

初始化bean又包含了相关生命周期要执行的逻辑

protected void invokeInitMethods(String beanName, final Object bean, @Nullable RootBeanDefinition mbd)      throws Throwable {   boolean isInitializingBean = (bean instanceof InitializingBean);   if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {          …        //执行afterPropertiesSet         ((InitializingBean) bean).afterPropertiesSet();       ...   }   if (mbd != null && bean.getClass() != NullBean.class) {      String initMethodName = mbd.getInitMethodName();      if (StringUtils.hasLength(initMethodName) &&            !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&            !mbd.isExternallyManagedInitMethod(initMethodName)) {        //执行自己的initMethod方法         invokeCustomInitMethod(beanName, bean, mbd);      }   }}复制代码

对于 RequestMappingHandlerMapping 继承了接口ApplicationContextAware和 InitializingBean,都属于bean生命周期中的一环。

ApplicationContextAware

RequestMappingHandlerMapping的父类自己持有一个applicationContext的引用

public final void setApplicationContext(@Nullable ApplicationContext context) throws BeansException {  ...   else if (this.applicationContext == null) {      ...      this.applicationContext = context;      this.messageSourceAccessor = new MessageSourceAccessor(context);      initApplicationContext(context);   }  ...}复制代码

从父类开始往下去执行对应的方法

protected void initApplicationContext() throws BeansException {   …   //探测所有的interceptor，即找到所有类MappedInterceptor【这对应 mvc-interceptor标签】和实现了接口HandlerInterceptor的拦截器   detectMappedInterceptors(this.adaptedInterceptors);   //初始化interceptor   initInterceptors();}复制代码

InitializingBean

public void afterPropertiesSet() {    …//getCandidateBeanNames默认就是获取所有的beanfor (String beanName : getCandidateBeanNames()) {    //判断 bean 的名字是否是 “scopedTarget.” 字符串开头   if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {      processCandidateBean(beanName);   }}    …}复制代码

查到bean后，开始识别是否是用来处理请求的

protected void processCandidateBean(String beanName) {   Class
     beanType = null;     ...      beanType = obtainApplicationContext().getType(beanName);     …   //isHandler即判断这个beanType是否包含注解 Controller 或者 RequestMapping   if (beanType != null && isHandler(beanType)) {    //找到这个注解bean的所有方法，构建映射关系      detectHandlerMethods(beanName);   }}protected boolean isHandler(Class
     beanType) {   return (AnnotatedElementUtils.hasAnnotation(beanType, Controller.class) ||         AnnotatedElementUtils.hasAnnotation(beanType, RequestMapping.class));}复制代码

探测handler的方法分成两个主要部分

1. 找到这个bean的所有的方法
2. 将方法注册

protected void detectHandlerMethods(Object handler) {      …      //找到这个bean的方法      Map
    
      methods = MethodIntrospector.selectMethods(userType,            (MethodIntrospector.MetadataLookup
     
      ) method -> {               try {                //找到方法对应的RequestMapping注解，将它的path等参数封装成RequestMappingInfo返回                  return getMappingForMethod(method, userType);               }               catch (Throwable ex) {                  throw new IllegalStateException("Invalid mapping on handler class [" +                        userType.getName() + "]: " + method, ex);               }            });     ...      methods.forEach((method, mapping) -> {         Method invocableMethod = AopUtils.selectInvocableMethod(method, userType);          //注册handler，在内部创建HandlerMethod，在urlLookup中存储 url和mapping的关系，而mapping和HandlerMethod则存储在mappingLookup中         registerHandlerMethod(handler, invocableMethod, mapping);      });    ...}复制代码
     
    

initViewResolvers

同handlerMapping,默认类为

org.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolver复制代码

根据view的名字来找到对应的View。View则负责来渲染内容

spring 处理请求到来

从可以看到，执行请求对应着的是servlet的service方法，对应spring来说，他就是DispatcherServlet

protected void doService(HttpServletRequest request, HttpServletResponse response) { …//请求总设置applicationContextrequest.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());…//进行请求分发doDispatch(request, response);…}doDispatch负责把一次请求分配给对应的handler来处理protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {  ...      ModelAndView mv = null;     ...         //如果请求存在分段文件，则转换成Multipart，比如MultipartHttpServletRequest         processedRequest = checkMultipart(request);         …        //获取对应请求的handler         mappedHandler = getHandler(processedRequest);        …        //返回这个hander对应的适配器，比如对于HandlerMethod子类返回的就是AbstractHandlerMethodAdapter         HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());        …        //调用interceptor的preHandle方法             if (!mappedHandler.applyPreHandle(processedRequest, response)) {           return;         }        …        //执行处理逻辑         mv = ha.handle(processedRequest, response, mappedHandler.getHandler());         …        //掉interceptor的postHandle方法         mappedHandler.applyPostHandle(processedRequest, response, mv);      ….    //处理结果     processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);      ...}复制代码

getHandler详细处理如下

public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {    //内部根据请求的路径执行lookupHandlerMethod(lookupPath, request)，而它就会从 urlLookup.get(urlPath)中查到对应的mapping,再查到HanlerMethod   Object handler = getHandlerInternal(request);   …   //匹配路径的拦截器全都加到handler链路里面来    HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);   ...   return executionChain;}复制代码

handler核心逻辑如下

protected ModelAndView invokeHandlerMethod(HttpServletRequest request,      HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {      ...       //将handlerMethod进行包装，以便后续通过反射执行      ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);        。。。      //创建ModelAndView的容器      ModelAndViewContainer mavContainer = new ModelAndViewContainer();        …        //通过反射执行      invocableMethod.invokeAndHandle(webRequest, mavContainer);      …      //获取ModeAndView,从内部可以看到，它会自行创建一个ModelAndView对象      return getModelAndView(mavContainer, modelFactory, webRequest);     ...}复制代码

获得handler的结果之后，调用processDispatchResult，核心就是进行render

private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,      @Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,      @Nullable Exception exception) throws Exception {      ...      render(mv, request, response);      ...}protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {  ….   View view;    //获取视图的名字   String viewName = mv.getViewName();    //根据名字获取对应的视图   view = resolveViewName(viewName, mv.getModelInternal(), locale, request);    …    //执行渲染      view.render(mv.getModelInternal(), request, response); ...}复制代码

执行render方法来源与所有render的父类AbstractView的render方法

@Overridepublic void render(@Nullable Map
    
      model, HttpServletRequest request,      HttpServletResponse response) throws Exception {    ….   Map
     
       mergedModel = createMergedOutputModel(model, request, response);   prepareResponse(request, response);   //真正执行渲染   renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);}复制代码
     
    

比如返回的是JSON对象，那么实际情况如下

protected void renderMergedOutputModel(Map
    
      model, HttpServletRequest request, HttpServletResponse response) throws Exception {    Object value = this.filterModel(model);    //值封装成json    String text = JSON.toJSONString(value, this.serializerFeatures);    byte[] bytes = text.getBytes(this.charset);    Object stream = this.updateContentLength?this.createTemporaryOutputStream():response.getOutputStream();    //结果写入outpuststream    ((OutputStream)stream).write(bytes);    if(this.updateContentLength) {        //返回        this.writeToResponse(response, (ByteArrayOutputStream)stream);    }}复制代码
    

对于Freemarker来说，就是执行FreemarkerView.renderMergedTemplateModel方法,内部执行doRender

protected void doRender(Map
    
      model, HttpServletRequest request,      HttpServletResponse response) throws Exception {    exposeModelAsRequestAttributes(model, request);    SimpleHash fmModel = buildTemplateModel(model, request, response);    Locale locale = RequestContextUtils.getLocale(request);    //这里就是调用Freemarker的template来处理对应的数据填充等等 template.process(model, response.getWriter());   processTemplate(getTemplate(locale), fmModel, response);}复制代码
    

至此一次请求结束