private ModelAndView invokeHandleMethod(HttpServletRequest request,
   HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

 ServletWebRequest webRequest = new ServletWebRequest(request, response);

 WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
 ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory); //根據handlerMethod和binderFactory創(chuàng)建一個ServletInvocableHandlerMethod。后續(xù)把請求直接交給ServletInvocableHandlerMethod執(zhí)行。
 //createRequestMappingMethod方法比較簡單，把之前RequestMappingHandlerAdapter初始化的argumentResolvers和returnValueHandlers添加至ServletInvocableHandlerMethod中
 ServletInvocableHandlerMethod requestMappingMethod = createRequestMappingMethod(handlerMethod, binderFactory);

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

 AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
 asyncWebRequest.setTimeout(this.asyncRequestTimeout); final 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();  if (logger.isDebugEnabled()) {
   logger.debug("Found concurrent result value [" + result + "]");
  }
  requestMappingMethod = requestMappingMethod.wrapConcurrentResult(result);
 }

 requestMappingMethod.invokeAndHandle(webRequest, mavContainer); if (asyncManager.isConcurrentHandlingStarted()) {  return null;
 } return getModelAndView(mavContainer, modelFactory, webRequest);
}

public final Object invokeForRequest(NativeWebRequest request,
          ModelAndViewContainer mavContainer,          Object... providedArgs) throws Exception {  //從request中解析出HandlerMethod方法所需要的參數，并返回Object[]
  Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);  if (logger.isTraceEnabled()) {
   StringBuilder builder = new StringBuilder("Invoking [");
   builder.append(this.getMethod().getName()).append("] method with arguments ");
   builder.append(Arrays.asList(args));
   logger.trace(builder.toString());
  }  
  //通過反射執(zhí)行HandleMethod中的method，方法參數為args。并返回方法執(zhí)行的返回值
  Object returnValue = invoke(args);  if (logger.isTraceEnabled()) {
   logger.trace("Method [" + this.getMethod().getName() + "] returned [" + returnValue + "]");
  }  return returnValue;
 }

private Object[] getMethodArgumentValues(
  NativeWebRequest request, ModelAndViewContainer mavContainer,  Object... providedArgs) throws Exception { 
  //獲取方法參數數組
 MethodParameter[] parameters = getMethodParameters(); 
 //創(chuàng)建一個參數數組，保存從request解析出的方法參數
 Object[] args = new Object[parameters.length]; for (int i = 0; i < parameters.length; i++) {
  MethodParameter parameter = parameters[i];
  parameter.initParameterNameDiscovery(parameterNameDiscoverer);
  GenericTypeResolver.resolveParameterType(parameter, getBean().getClass());

  args[i] = resolveProvidedArgument(parameter, providedArgs);  if (args[i] != null) {   continue;
  }  
  //判斷之前RequestMappingHandlerAdapter初始化的那24個HandlerMethodArgumentResolver（參數解析器），是否存在支持該參數解析的解析器
  if (argumentResolvers.supportsParameter(parameter)) {   try {
    args[i] = argumentResolvers.resolveArgument(parameter, mavContainer, request, dataBinderFactory);    continue;
   } catch (Exception ex) {    if (logger.isTraceEnabled()) {
     logger.trace(getArgumentResolutionErrorMessage("Error resolving argument", i), ex);
    }    throw ex;
   }
  }  if (args[i] == null) {   String msg = getArgumentResolutionErrorMessage("No suitable resolver for argument", i);   throw new IllegalStateException(msg);
  }
 } return args;
}

public Object resolveArgument(
   MethodParameter parameter, ModelAndViewContainer mavContainer,
   NativeWebRequest webRequest, WebDataBinderFactory binderFactory)
   throws Exception {  
   //首先獲取參數解析器，這里獲取的邏輯是首先從argumentResolverCache緩存中獲取該MethodParameter匹配的HandlerMethodArgumentResolver。如果為空，遍歷初始化定義的那24個。查找匹配的HandlerMethodArgumentResolver，然后添加至argumentResolverCache緩存中
  HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter);
  Assert.notNull(resolver, "Unknown parameter type [" + parameter.getParameterType().getName() + "]");  
  //解析參數
  return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory);
 }

public final Object resolveArgument(
   MethodParameter parameter, ModelAndViewContainer mavContainer,
   NativeWebRequest webRequest, WebDataBinderFactory binderFactory)
   throws Exception {  
   //獲取int的Class對象
  Class<?> paramType = parameter.getParameterType();  
  //根據參數定義創(chuàng)建一個NamedValueInfo對象
  NamedValueInfo namedValueInfo = getNamedValueInfo(parameter);  //根據參數名解析出對象的值
  Object arg = resolveName(namedValueInfo.name, parameter, webRequest);  if (arg == null) {   if (namedValueInfo.defaultValue != null) {
    arg = resolveDefaultValue(namedValueInfo.defaultValue);
   }   else if (namedValueInfo.required) {
    handleMissingValue(namedValueInfo.name, parameter);
   }
   arg = handleNullValue(namedValueInfo.name, arg, paramType);
  }  else if ("".equals(arg) && (namedValueInfo.defaultValue != null)) {
   arg = resolveDefaultValue(namedValueInfo.defaultValue);
  }  
  //上面步驟獲取的args是String類型，然后轉換為方法參數所需要的類型(int)
  if (binderFactory != null) {
   WebDataBinder binder = binderFactory.createBinder(webRequest, null, namedValueInfo.name);
   arg = binder.convertIfNecessary(arg, paramType, parameter);
  }

  handleResolvedValue(arg, namedValueInfo.name, parameter, mavContainer, webRequest);  
  return arg;
 }

/**
*帶有@ModelAttribute注解返回true
* parameter不是簡單類型也返回true.
*/
public boolean supportsParameter(MethodParameter parameter) {
 if (parameter.hasParameterAnnotation(ModelAttribute.class)) {  
  return true;
 } else if (this.annotationNotRequired) {   
  return !BeanUtils.isSimpleProperty(parameter.getParameterType());
 } else {   
  return false;
 }
}

/**
* 解析model中的參數，如果從ModelAndViewContainer未找到，直接通過反射實例化一個對象。具體實例化是通過父類的createAttribute方法，通過調用BeanUtils.instantiateClass方法來實例化的。這個對象便是后續(xù)傳給test2(User u)方法的對象，但是此時創(chuàng)建的對象里面的值都還為空，注入值是通過bindRequestParameters方法來實現(xiàn)的。
*/
public final Object resolveArgument(
 MethodParameter parameter, ModelAndViewContainer mavContainer,
   NativeWebRequest request, WebDataBinderFactory binderFactory)
  throws Exception {  
 String name = ModelFactory.getNameForParameter(parameter);  Object attribute = (mavContainer.containsAttribute(name)) ?
 mavContainer.getModel().get(name) : createAttribute(name, parameter, binderFactory, request);
 WebDataBinder binder = binderFactory.createBinder(request, attribute, name);  
 if (binder.getTarget() != null) {   
 //將請求綁定至目標binder的target對象，也就是剛剛創(chuàng)建的attribute對象。
 bindRequestParameters(binder, request);   
 //如果有驗證，則驗證參數
 validateIfApplicable(binder, parameter);   
 if (binder.getBindingResult().hasErrors()) {    
  if (isBindExceptionRequired(binder, parameter)) {   
   throw new BindException(binder.getBindingResult());
    }
   }
  }  
  // Add resolved attribute and BindingResult at the end of the model

  Map<String, Object> bindingResultModel = binder.getBindingResult().getModel();
  mavContainer.removeAttributes(bindingResultModel);
  mavContainer.addAllAttributes(bindingResultModel);  
  return binder.getTarget();
 }