带你详解SpringMVC从基础到源码

/**
* 建立当前ApplicationContext中的所有controller和url的对应关系
*/
protected void detectHandlers() throws BeansException {
  //日志级别是否是 Debug
  if (logger.isDebugEnabled()) {
    //应用上下文就是工程的访问路径
    logger.debug("Looking for URL mappings in application context: " + getApplicationContext());
  }
　　　　 // 获取ApplicationContext容器中所有bean的Name---Controller
  String[] beanNames = (this.detectHandlersInAncestorContexts ?
      BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(), Object.class) :
      getApplicationContext().getBeanNamesForType(Object.class));

  // 遍历beanNames,并找到这些bean对应的url
  for (String beanName : beanNames) {
　　　　　　 // 获取Controller上的所有url(类上的url+方法上的url)
    String[] urls = determineUrlsForHandler(beanName);
    if (!ObjectUtils.isEmpty(urls)) {
      // 保存urls和beanName的对应关系,put it to Map<urls,beanName>,该方法在父类AbstractUrlHandlerMapping中实现
      registerHandler(urls, beanName);
    }
    else {
      if (logger.isDebugEnabled()) {
        logger.debug("Rejected bean name '" + beanName + "': no URL paths identified");
      }
    }
  }
}

/** 中央控制器,控制请求的转发 **/
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
int interceptorIndex = -1;

try {
  ModelAndView mv;
  boolean errorView = false;
  try {
　　　　// 1.检查是否是文件上传的请求
    processedRequest = checkMultipart(request);

    // 2.取得处理当前请求的controller,这里也称为hanlder,处理器,第一个步骤的意义就在这里体现了.
    这里并不是直接返回controller,而是返回的HandlerExecutionChain请求处理器链对象，该对象封装了handler和interceptors.
    mappedHandler = getHandler(processedRequest, false);
　　　　// 如果handler为空,则返回404
    if (mappedHandler == null || mappedHandler.getHandler() == null) {
      noHandlerFound(processedRequest, response);
      return;
    }
    //3. 获取处理request的处理器适配器handler adapter 
    HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
    // 处理 last-modified 请求头
    String method = request.getMethod();
    boolean isGet = "GET".equals(method);
    if (isGet || "HEAD".equals(method)) {
      long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
      if (logger.isDebugEnabled()) {
        String requestUri = urlPathHelper.getRequestUri(request);
        logger.debug("Last-Modified value for [" + requestUri + "] is: " + lastModified);
      }
      if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
        return;
      }
    }

    // 4.拦截器的预处理方法
    HandlerInterceptor[] interceptors = mappedHandler.getInterceptors();
    if (interceptors != null) {
      for (int i = 0; i < interceptors.length; i++) {
        HandlerInterceptor interceptor = interceptors[i];
        if (!interceptor.preHandle(processedRequest, response, mappedHandler.getHandler())) {
          triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null);
          return;
        }
        interceptorIndex = i;
      }
    }

    // 5.实际的处理器处理请求,返回结果视图对象
    mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

    // 结果视图对象的处理
    if (mv != null && !mv.hasView()) {
      mv.setViewName(getDefaultViewName(request));
    }

    // 6.拦截器的后处理方法
    if (interceptors != null) {
      for (int i = interceptors.length - 1; i >= 0; i--) {
        HandlerInterceptor interceptor = interceptors[i];
        interceptor.postHandle(processedRequest, response, mappedHandler.getHandler(), mv);
      }
    }
  }
  catch (ModelAndViewDefiningException ex) {
    logger.debug("ModelAndViewDefiningException encountered", ex);
    mv = ex.getModelAndView();
  }
  catch (Exception ex) {
    Object handler = (mappedHandler != null &#63; mappedHandler.getHandler() : null);
    mv = processHandlerException(processedRequest, response, handler, ex);
    errorView = (mv != null);
  }

  
  if (mv != null && !mv.wasCleared()) {
    render(mv, processedRequest, response);
    if (errorView) {
      WebUtils.clearErrorRequestAttributes(request);
    }
  }
  else {
    if (logger.isDebugEnabled()) {
      logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +
          "': assuming HandlerAdapter completed request handling");
    }
  }

  // 请求成功响应之后的方法
  triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null);
}

/** 获取处理请求的方法,执行并返回结果视图 **/
protected ModelAndView invokeHandlerMethod(HttpServletRequest request, HttpServletResponse response, Object handler)
	throws Exception {
　 // 1.获取方法解析器
  ServletHandlerMethodResolver methodResolver = getMethodResolver(handler);　　　　 
  // 2.解析request中的url,获取处理request的方法 
  //通过 request 找 controller 中的处理方法，request的url与 controller 的url 进行匹配
  Method handlerMethod = methodResolver.resolveHandlerMethod(request);　　　　 
  // 3.方法调用器
  ServletHandlerMethodInvoker methodInvoker = new ServletHandlerMethodInvoker(methodResolver);
  ServletWebRequest webRequest = new ServletWebRequest(request, response);
  ExtendedModelMap implicitModel = new BindingAwareModelMap();
　　　　 // 4.执行方法
  Object result = methodInvoker.invokeHandlerMethod(handlerMethod, handler, webRequest, implicitModel);　　　　 
  // 5.封装结果视图
  ModelAndView mav =
      methodInvoker.getModelAndView(handlerMethod, handler.getClass(), result, implicitModel, webRequest);
  methodInvoker.updateModelAttributes(handler, (mav != null ? mav.getModel() : null), implicitModel, webRequest);
  return mav;
}