spring mvc 5.1.1.RELEASE的一次請求過程源碼分析

從Jetty啓動流程能夠看到,啓動上下文以後，緊接着就開始初始化servlet,調用init方法

private synchronized void initServlet()
        throws ServletException
    {
        ...
        //調用Servlet的init方法
        _servlet.init(_config);
        ...
    }
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從web.xml文件中能夠看到，這個servlet就是DispatcherServlet,對應的init方法在父類GenericServlet中

public void init(ServletConfig config) throws ServletException {
//這裏servletconfig就被傳下來
this.config = config;
//執行子類的init方法
this.init();
}
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對應在 HttpServletBean中

public final void init() throws ServletException {
    ...
    initServletBean();
}
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在FrameworkServlet中實現對應的spring的servlet的初始化

protected final void initServletBean() throws ServletException {
…
this.webApplicationContext = initWebApplicationContext();
…
}
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對應的初始化web容器，首先也會去查詢是否已經初始化過了

protected WebApplicationContext initWebApplicationContext() {
    //獲取根webapplicationcontext，這就是在IOC容器初始化的時候塞入的值，若是IoC容器已經初始化完成，那麼這裏的值確定不是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()) {
       //若是沒有執行過webcontextapplication的refresh,那麼再執行一次
    if (cwac.getParent() == null) {
         cwac.setParent(rootContext);
      }
      //這個過程就相似IOC的啓動了
      configureAndRefreshWebApplicationContext(cwac);
   }
}
   }
   ...
   if (!this.refreshEventReceived) {
      //沒有執行過refresh則執行一次
      onRefresh(wac);
   }
    ….
   return wac;
}
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對於這個時間點的DispatcherServlet啓動來講，核心在於 onRefresh,它會去初始化各類resolver

protected void onRefresh(ApplicationContext context) {
 …
initMultipartResolver(context);
...
initHandlerMappings(context);
...
initViewResolvers(context);
 …
}
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MultipartResolver

它會從容器中讀取是否包含 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); ... } 複製代碼

MultipartResolver是用來解決文件上傳問題

HandlerMappings

默認本身去掃描全部HandlerMapping類型的

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

   if (this.detectAllHandlerMappings) {
    //默認這裏執行主動探測，這裏的實現其實就是從BeanFactory中獲取全部已經註冊了的，且類型是HandlerMapping的類的名字，而後再從BeanFactory中獲取全部這個名字的bean做爲返回
      Map<String, HandlerMapping> 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) {
      //沒有handlerMapping，則使用默認的。
      this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
      if (logger.isTraceEnabled()) {
         logger.trace("No HandlerMappings declared for servlet '" + getServletName() +
               "': using default strategies from DispatcherServlet.properties");
      }
   }
}
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在沒有配置的狀況下，處理映射的類配置在spring自帶的文件DispatcherServlet.properties中，默認handlerMapping的類爲

org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\   org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping
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HandlerMapping負責定義請求和處理請求的對象之間的映射

以RequestMappingHandlerMapping爲例。當獲取到對應的名字後

protected <T> List<T> getDefaultStrategies(ApplicationContext context, Class<T> strategyInterface) {
   String key = strategyInterface.getName();
  //獲取默認的配置
   String value = defaultStrategies.getProperty(key);
     ….
    //經過反射構建class對象
            Class<?> clazz = ClassUtils.forName(className, DispatcherServlet.class.getClassLoader());
    //從beanFactory中獲取對象，其實就是調用createBean方法
            Object strategy = createDefaultStrategy(context, clazz);
            strategies.add((T) strategy);
         }
        ….
}
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對於beanFactory來講，建立一個bean或經歷它的完整生命週期，通過多層查找，能夠看到以下代碼

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);
...
}
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執行一些列的生命名週期方法

protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
   ...
   //執行各類aware方法
      invokeAwareMethods(beanName, bean);
   …
    //執行初始化以前的BeanPostProcessor相關方法
      wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
   
   …
   //執行初始化bean方法
      invokeInitMethods(beanName, wrappedBean, mbd);
    …
    //執行初始化以後的BeanPostProcessor相關方法
      wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
   ...

}
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-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);
     }
  }
}
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初始化bean又包含了相關生命週期要執行的邏輯

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"))) {
          …
        //執行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)) {
        //執行本身的initMethod方法
         invokeCustomInitMethod(beanName, bean, mbd);
      }
   }
}
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對於 RequestMappingHandlerMapping 繼承了接口ApplicationContextAware和 InitializingBean,都屬於bean生命週期中的一環。

ApplicationContextAware

RequestMappingHandlerMapping的父類本身持有一個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);
   }
  ...
}
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從父類開始往下去執行對應的方法

protected void initApplicationContext() throws BeansException {
   …
   //探測全部的interceptor，即找到全部類MappedInterceptor【這對應 mvc-interceptor標籤】和實現了接口HandlerInterceptor的攔截器
   detectMappedInterceptors(this.adaptedInterceptors);
   //初始化interceptor
   initInterceptors();
}
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InitializingBean

public void afterPropertiesSet() {
    …
//getCandidateBeanNames默認就是獲取全部的bean
for (String beanName : getCandidateBeanNames()) {
    //判斷 bean 的名字是不是 「scopedTarget.」 字符串開頭
   if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
      processCandidateBean(beanName);
   }
}
    …
}
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查到bean後，開始識別是不是用來處理請求的

protected void processCandidateBean(String beanName) {
   Class<?> beanType = null;
     ...
      beanType = obtainApplicationContext().getType(beanName);
     …
   //isHandler即判斷這個beanType是否包含註解 Controller 或者 RequestMapping
   if (beanType != null && isHandler(beanType)) {
    //找到這個註解bean的全部方法，構建映射關係
      detectHandlerMethods(beanName);
   }
}

protected boolean isHandler(Class<?> beanType) {
   return (AnnotatedElementUtils.hasAnnotation(beanType, Controller.class) ||
         AnnotatedElementUtils.hasAnnotation(beanType, RequestMapping.class));
}
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探測handler的方法分紅兩個主要部分

1. 找到這個bean的全部的方法
2. 將方法註冊

protected void detectHandlerMethods(Object handler) {
      …
      //找到這個bean的方法
      Map<Method, T> methods = MethodIntrospector.selectMethods(userType,
            (MethodIntrospector.MetadataLookup<T>) method -> {
               try {
                //找到方法對應的RequestMapping註解，將它的path等參數封裝成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);
          //註冊handler，在內部建立HandlerMethod，在urlLookup中存儲 url和mapping的關係，而mapping和HandlerMethod則存儲在mappingLookup中
         registerHandlerMethod(handler, invocableMethod, mapping);
      });
    ...
}

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initViewResolvers

同handlerMapping,默認類爲

org.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolver
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根據view的名字來找到對應的View。View則負責來渲染內容

spring 處理請求到來

從Jetty請求過程能夠看到，執行請求對應着的是servlet的service方法，對應spring來講，他就是DispatcherServlet

protected void doService(HttpServletRequest request, HttpServletResponse response) {
 …
//請求總設置applicationContext
request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
…
//進行請求分發
doDispatch(request, response);
…
}
doDispatch負責把一次請求分配給對應的handler來處理
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
  ...
      ModelAndView mv = null;
     ...
         //若是請求存在分段文件，則轉換成Multipart，好比MultipartHttpServletRequest
         processedRequest = checkMultipart(request);
         …
        //獲取對應請求的handler
         mappedHandler = getHandler(processedRequest);
        …
        //返回這個hander對應的適配器，好比對於HandlerMethod子類返回的就是AbstractHandlerMethodAdapter
         HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
        …
        //調用interceptor的preHandle方法
     
        if (!mappedHandler.applyPreHandle(processedRequest, response)) {
           return;
         }
        …
        //執行處理邏輯
         mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
         …
        //掉interceptor的postHandle方法
         mappedHandler.applyPostHandle(processedRequest, response, mv);
      ….
    //處理結果
     processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
      ...
}
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getHandler詳細處理以下

public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
    //內部根據請求的路徑執行lookupHandlerMethod(lookupPath, request)，而它就會從 urlLookup.get(urlPath)中查到對應的mapping,再查到HanlerMethod
   Object handler = getHandlerInternal(request);
   …
   //匹配路徑的攔截器全都加到handler鏈路裏面來 
   HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
   ...
   return executionChain;
}
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handler核心邏輯以下

protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
      HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
      ...
       //將handlerMethod進行包裝，以便後續經過反射執行
      ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
        。。。

      //建立ModelAndView的容器
      ModelAndViewContainer mavContainer = new ModelAndViewContainer();
        …
        //經過反射執行
      invocableMethod.invokeAndHandle(webRequest, mavContainer);
      …
      //獲取ModeAndView,從內部能夠看到，它會自行建立一個ModelAndView對象
      return getModelAndView(mavContainer, modelFactory, webRequest);
     ...
}
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得到handler的結果以後，調用processDispatchResult，核心就是進行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;
    //獲取視圖的名字
   String viewName = mv.getViewName();
    //根據名字獲取對應的視圖
   view = resolveViewName(viewName, mv.getModelInternal(), locale, request);
    …
    //執行渲染
      view.render(mv.getModelInternal(), request, response);
 ...
}
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執行render方法來源與全部render的父類AbstractView的render方法

@Overridepublic void render(@Nullable Map<String, ?> model, HttpServletRequest request,
      HttpServletResponse response) throws Exception {
    ….
   Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);
   prepareResponse(request, response);
   //真正執行渲染
   renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);
}
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好比返回的是JSON對象，那麼實際狀況以下

protected void renderMergedOutputModel(Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception {
    Object value = this.filterModel(model);
    //值封裝成json
    String text = JSON.toJSONString(value, this.serializerFeatures);
    byte[] bytes = text.getBytes(this.charset);
    Object stream = this.updateContentLength?this.createTemporaryOutputStream():response.getOutputStream();
    //結果寫入outpuststream
    ((OutputStream)stream).write(bytes);
    if(this.updateContentLength) {
        //返回
        this.writeToResponse(response, (ByteArrayOutputStream)stream);
    }

}
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對於Freemarker來講，就是執行FreemarkerView.renderMergedTemplateModel方法,內部執行doRender

protected void doRender(Map<String, Object> model, HttpServletRequest request,
      HttpServletResponse response) throws Exception {

    exposeModelAsRequestAttributes(model, request);
    SimpleHash fmModel = buildTemplateModel(model, request, response);

    Locale locale = RequestContextUtils.getLocale(request);
    //這裏就是調用Freemarker的template來處理對應的數據填充等等 template.process(model, response.getWriter());
   processTemplate(getTemplate(locale), fmModel, response);
}
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至此一次請求結束