【SpringMVC从入门到精通】09-SpringMVC 执行流程

2022/4/6 6:19:26

本文主要是介绍【SpringMVC从入门到精通】09-SpringMVC 执行流程,对大家解决编程问题具有一定的参考价值,需要的程序猿们随着小编来一起学习吧!

笔记来源:【尚硅谷】SpringMVC教程丨一套快速上手spring mvc

目录
  • SpringMVC 执行流程
    • 1、SpringMVC 常用组件
    • 2、DispatcherServlet 初始化过程
      • 2.1、初始化 WebApplicationContext
      • 2.2、创建 WebApplicationContext
      • 2.3、DispatcherServlet 初始化策略
    • 3、DispatcherServlet 调用组件处理请求
      • 3.1、processRequest
      • 3.2、doService
      • 3.3、doDispatch
      • 3.4、processDispatchResult
    • 4、SpringMVC 执行流程
    • 总结

SpringMVC 执行流程

1、SpringMVC 常用组件

  • DispatcherServlet前端控制器,不需要工程师开发,由框架提供
    • 作用:统一处理请求和响应,整个流程控制的中心,由它调用其它组件处理用户的请求
  • HandlerMapping处理器映射器,不需要工程师开发,由框架提供
    • 作用:根据请求的 url、method 等信息查找Handler,即控制器方法
  • Handler处理器,需要工程师开发
    • 作用:在DispatcherServlet的控制下Handler对具体的用户请求进行处理
  • HandlerAdapter处理器适配器,不需要工程师开发,由框架提供
    • 作用:通过HandlerAdapter对处理器(控制器方法)进行执行
  • ViewResolver视图解析器,不需要工程师开发,由框架提供
    • 作用:进行视图解析,得到相应的视图,例如:ThymeleafViewInternalResourceViewRedirectView
  • View视图
    • 作用:将模型数据通过页面展示给用户

2、DispatcherServlet 初始化过程

DispatcherServlet本质上是一个 Servlet,所以天然的遵循 Servlet 的生命周期,宏观上是 Servlet 生命周期来进行调度

image-20220406004101035

image-20220406004325136

2.1、初始化 WebApplicationContext

所在类:org.springframework.web.servlet.FrameworkServlet

protected WebApplicationContext initWebApplicationContext() {
    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();
    }
    if (wac == null) {
        // 创建ApplicationContext
        wac = createWebApplicationContext(rootContext);
    }
    if (!this.refreshEventReceived) {
        synchronized (this.onRefreshMonitor) {
            // 刷新ApplicationContext
            onRefresh(wac);
        }
    }
    if (this.publishContext) {
        String attrName = getServletContextAttributeName();
        // 将IOC容器在应用域共享
        getServletContext().setAttribute(attrName, wac);
    }
    return wac;
}

2.2、创建 WebApplicationContext

所在类:org.springframework.web.servlet.FrameworkServlet

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");
    }
    // 反射创建IOC容器对象
    ConfigurableWebApplicationContext wac =
        (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
    wac.setEnvironment(getEnvironment());
    // 设置父容器:将Spring上下文对象作为SpringMVC上下文对象的父容器
    wac.setParent(parent);
    String configLocation = getContextConfigLocation();
    if (configLocation != null) {
        wac.setConfigLocation(configLocation);
    }
    configureAndRefreshWebApplicationContext(wac);
    return wac;
}

2.3、DispatcherServlet 初始化策略

FrameworkServlet创建WebApplicationContext后,调用onRefresh(wac)刷新容器

此方法在DispatcherServlet中进行了重写,调用了initStrategies(context)方法,初始化策略,即初始化DispatcherServlet的各个组件

所在类:org.springframework.web.servlet.DispatcherServlet

protected void initStrategies(ApplicationContext context) {
    // 初始化文件上传解析器
    initMultipartResolver(context);
    initLocaleResolver(context);
    initThemeResolver(context);
    // 初始化处理器映射
    initHandlerMappings(context);
    // 初始化处理器适配器
    initHandlerAdapters(context);
    // 初始化处理器异常处理器
    initHandlerExceptionResolvers(context);
    initRequestToViewNameTranslator(context);
    // 初始化视图解析器
    initViewResolvers(context);
    initFlashMapManager(context);
}

3、DispatcherServlet 调用组件处理请求

3.1、processRequest

FrameworkServlet重写HttpServlet中的service()doXxx(),这些方法中调用了processRequest(request,response)

所在类:org.springframework.web.servlet.FrameworkServlet

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());
    
    initContextHolders(request, localeContext, requestAttributes);
    try {
        // 重点关注
        doService(request, response);
    }
    catch (ServletException | IOException ex) {
        failureCause = ex;
        throw ex;
    }
    catch (Throwable ex) {
        failureCause = ex;
        throw new NestedServletException("Request processing failed", ex);
    }
    finally {
        resetContextHolders(request, previousLocaleContext, previousAttributes);
        if (requestAttributes != null) {
            requestAttributes.requestCompleted();
        }
        logResult(request, response, failureCause, asyncManager);
        publishRequestHandledEvent(request, response, startTime, failureCause);
    }
}

3.2、doService

所在类:org.springframework.web.servlet.DispatcherServlet

protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
    logRequest(request);
    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));
            }
        }
    }
    
    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 {
        // 重点关注
        doDispatch(request, response);
    }
    finally {
        if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
            if (attributesSnapshot != null) {
                restoreAttributesAfterInclude(request, attributesSnapshot);
            }
        }
        if (this.parseRequestPath) {
            ServletRequestPathUtils.setParsedRequestPath(previousRequestPath, request);
        }
    }
}

3.3、doDispatch

所在类:org.springframework.web.servlet.DispatcherServlet

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);
            // 包含handler、interceptorList、interceptorIndex 
            // 		handler:浏览器发送的请求所匹配的控制器方法
            // 		interceptorList:处理控制器方法的所有拦截器集合 
            // 		interceptorIndex:拦截器索引,控制拦截器aftercompletion()的执行
            mappedHandler = getHandler(processedRequest);
            if (mappedHandler == null) {
                noHandlerFound(processedRequest, response);
                return;
            }
			// 创建处理器适配器,负责调用控制器方法
            HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
            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;
                }
            }
            // 调用拦截器preHandle方法,正序执行
            if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                return;
            }
            // 由处理器适配器调用具体的控制器方法,最终获得ModelAndview对象
            mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
            if (asyncManager.isConcurrentHandlingStarted()) {
                return;
            }
            applyDefaultViewName(processedRequest, mv);
            // 调用拦截器postHandle方法,反序执行
            mappedHandler.applyPostHandle(processedRequest, response, mv);
        }
        catch (Exception ex) {
            dispatchException = ex;
        }
        catch (Throwable err) {
            dispatchException = new NestedServletException("Handler dispatch failed", err);
        }
        // 后续处理:处理模型数据和渲染视图
        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);
            }
        }
    }
}

3.4、processDispatchResult

所在类:org.springframework.web.servlet.DispatcherServlet

private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
                                   @Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
                                   @Nullable Exception exception) throws Exception {
    boolean errorView = false;
    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);
        }
    }
    if (mv != null && !mv.wasCleared()) {
        // 处理模型数据和渲染视图
        render(mv, request, response);
        if (errorView) {
            WebUtils.clearErrorRequestAttributes(request);
        }
    }
    else {
        if (logger.isTraceEnabled()) {
            logger.trace("No view rendering, null ModelAndView returned.");
        }
    }
    if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
        return;
    }
    if (mappedHandler != null) {
        // 调用拦截器afterCompletion方法,反序执行
        mappedHandler.triggerAfterCompletion(request, response, null);
    }
}

4、SpringMVC 执行流程

1)用户向服务器发送请求,请求被 SpringMVC 前端控制器DispatcherServlet捕获

2)DispatcherServlet对请求 URL 进行解析,得到请求资源标识符 URI ,判断请求 URI 对应的映射是否存在:

若不存在,再判断是否配置了mvc:default-servlet-handler

  • i.如果没配置,则控制台报映射查找不到,客户端展示 404 错误
DEBUG org.springframework.web.servlet.Dispatcherservlet - GET "/springMVC/testHaha", parameters={}
WARN org.springframework.web.servlet.PageNotFound - No mapping for GET /springMVC/testHaha 
DEBUG org.springframework.web.servlet.Dispatcherservlet - Completed 404 NOT_FOUND
  • ii.如果有配置,则访问目标资源(一般为静态资源,如:JS,CSS,HTML),找不到客户端也会展示404错误
  DEBUG org.springframework.web.servlet.Dispatcherservlet - GET "/springMVC/testHaha", parameters={}
  handler.SimpleUrlHandlerMapping Mapped to org.springframework.web.servlet.resource.DefaultServletHttpRequestHandlerDispatcherservlet - Completed 404 NOT_FOUND

若存在,则执行一下流程

3)根据该 URI,调用HandlerMapping获得该Handler配置的所有相关的对象(包括Handler对象以及Handler对象对应的拦截器),最后以HandlerExecutionChain执行链对象的形式返回

4)DispatcherServlet根据获得的Handler,选择一个合适的HandlerAdapter

5)如果成功获得HandlerAdapter,此时将开始执行拦截器的preHandler()方法【正向】

6)提取 Request 中的模型数据,填充Handler入参,开始执行Handler(Controller)方法,处理请求。在填充Handler的入参过程中,根据你的配置,Spring 将帮你做一些额外的工作:

  • a)HttpMessageConveter:将请求消息(如 json、xml 等数据)转换成一个对象,将对象转换为指定的响应信息
  • b)数据转换:对请求消息进行数据转换。如 String 转换成 Integer、Double 等
  • c)数据格式化:对请求消息进行数据格式化。如将字符串转换成格式化数字或格式化日期等
  • d)数据验证:验证数据的有效性(长度、格式等),验证结果存储到 BindingResult 或 Error 中

7)Handler执行完成后,向DispatcherServlet返回一个ModelAndView对象

8)此时将开始执行拦截器的postHandle()方法【逆向】

9)根据返回的ModelAndView(此时会判断是否存在异常,如果存在异常,则执行HandlerExceptionResolver进行异常处理)选择一个适合的ViewResolver进行视图解析,根据ModelView,来渲染视图

10)渲染视图完毕执行拦截器的afterCompletion()方法【逆向】

11)将渲染结果返回给客户端

总结

本届重点掌握

  • SpringMVC 常用组件
  • DispatcherServlet 的初始化过程和调用方法
  • SpringMVC 执行流程

附上导图,仅供参考

09-SpringMVC 执行流程



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