SpringMVC源码解析系列4-HandleAdapter

时间 2019-11-17

标签 springmvc 源码解析系列 handleadapter 栏目 Spring 繁體版

原文原文链接

SpringMVC源码解析系列3-HandleAdapter

SpringMVC源码解析系列3-HandleAdapter

HandleAdapter接口定义

定义: 根据HandlerMethod信息,对http请求进行参数解析,并完成调用java

先看一下HandlerAdapter的接口定义web

public interface HandlerAdapter {
   //判断是否支持该handler类型的解析
   boolean supports(Object handler);
   //参数解析 并调用handler完成过程调用 
   ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;
   //用于处理http请求头中的last-modified
   long getLastModified(HttpServletRequest request, Object handler);

}

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RequestMappingHandlerAdapter

以RequestMappingHandlerAdapter为例来说,先看下继承关系spring

初始化过程

同RequestMappingHandlerMapping都有ApplicationContextAware,ServletContextAware,InitializingBean三个生命周期方法json

这里咱们就直接看InitializingBean了浏览器

#org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter
@Override
public void afterPropertiesSet() {
 // 1.装载@ControllerAdvice注解的类
 initControllerAdviceCache();
// 2.装载ArgumentResolver(默认+自定义)
 if (this.argumentResolvers == null) {
    List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
    //包装成一个Composite对象
    this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
 }
 // 2.装载InitBinderArgumentResolvers(默认+自定义)
 if (this.initBinderArgumentResolvers == null) {
    List<HandlerMethodArgumentResolver> resolvers = getDefaultInitBinderArgumentResolvers();
    //包装成一个Composite对象
    this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
 }
 // 3.装载ReturnValueHandlers(默认+自定义)
 if (this.returnValueHandlers == null) {
    List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
    //包装成一个Composite对象
    this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
 }
}
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过程归纳:缓存

装载带有ControllerAdvices注解的对象bash

private void initControllerAdviceCache() {
  //从容器中获取全部带有ControllerAdvices注解的类名 并包装成ControllerAdviceBean
  List<ControllerAdviceBean> beans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());
  OrderComparator.sort(beans);
  List<Object> responseBodyAdviceBeans = new ArrayList<Object>();
  for (ControllerAdviceBean bean : beans) {
    //筛选出带有@ModelAttribute且不带@RequestMapping注解的方法
    Set<Method> attrMethods = HandlerMethodSelector.selectMethods(bean.getBeanType(), MODEL_ATTRIBUTE_METHODS);
    if (!attrMethods.isEmpty()) {
      //保存到modelAttributeAdviceCache中
      this.modelAttributeAdviceCache.put(bean, attrMethods);
    }
    //筛选出带InitBinder注解的方法 添加到initBinderAdviceCache中
    Set<Method> binderMethods = HandlerMethodSelector.selectMethods(bean.getBeanType(), INIT_BINDER_METHODS);
    if (!binderMethods.isEmpty()) {
      this.initBinderAdviceCache.put(bean, binderMethods);
    }
    //筛选实现RequestBodyAdvice接口 添加到requestResponseBodyAdviceBeans中
    if (RequestBodyAdvice.class.isAssignableFrom(bean.getBeanType())) {
      requestResponseBodyAdviceBeans.add(bean);
      if (logger.isInfoEnabled()) {
        logger.info("Detected RequestBodyAdvice bean in " + bean);
      }
    }
    //筛选实现ResponseBodyAdvice接口 添加到requestResponseBodyAdviceBeans中
    if (ResponseBodyAdvice.class.isAssignableFrom(bean.getBeanType())) {
      requestResponseBodyAdviceBeans.add(bean);
      if (logger.isInfoEnabled()) {
        logger.info("Detected ResponseBodyAdvice bean in " + bean);
      }
    }
  }
  //保存到全局变量
  if (!responseBodyAdviceBeans.isEmpty()) {
    this.responseBodyAdvice.addAll(0, responseBodyAdviceBeans);
  }
}
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筛选出带有@ModelAttribute且不带@RequestMapping注解的方法
筛选出带InitBinder注解的方法添加到initBinderAdviceCache中
筛选实现RequestBodyAdvice接口添加到responseBodyAdvice中
筛选实现ResponseBodyAdvice接口添加到responseBodyAdvice中

装载ArgumentResolvers(默认+自定义)session
装载InitBinderArgumentResolvers(默认+自定义)mvc
装载ReturnValueHandlers(默认+自定义)app

自定义拓展方式放后面说

如下为HandlerAdapter默认解析器

HandlerMethodReturnValueHandler,HandlerMethodArgumentResolver

//参数解析器
public interface HandlerMethodArgumentResolver {
  //判断是否支持该参数的解析(根据类型,注解等)
   boolean supportsParameter(MethodParameter parameter);
  //对参数进行解析 获得解析结果
   Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception;
}
//返回值解析器
public interface HandlerMethodReturnValueHandler {
  //判断是否支持该返回值的解析(根据类型,注解等)
	boolean supportsReturnType(MethodParameter returnType);
  //对返回值进行解析
	void handleReturnValue(Object returnValue, MethodParameter returnType, ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception;
}

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DispatcherServlet调用HandlerAdapter过程

//1.调用support()方法判断是否支持HandlerMethod的解析
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// 若是是Get或Head请求 调用getLastModified()获取上次更新时间 
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
   long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
   if (logger.isDebugEnabled()) {
      logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
   }
  //若是小于浏览器缓存更新时间 则直接返回 浏览器使用本地缓存
   if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
      return;
   }
}
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
   return;
}
// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
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过程总结:

调用support()方法判断是否支持改handler的解析

#org.springframework.web.servlet.DispatcherServlet
//在doDispatch()方法中调用了getHandlerAdapter(Object)方法来获得一个HandlerAdapter
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
    //调用HandlerAdapter.support()方法 判断是否支持该handler对象的解析
   for (HandlerAdapter ha : this.handlerAdapters) {
        ...
      if (ha.supports(handler)) {
         return ha;
      }
   }
  ...
}
#org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter
//根据handler对象判断是否支持handler解析
@Override
public final boolean supports(Object handler) {
	return (handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler));
}
#org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter
@Override
protected boolean supportsInternal(HandlerMethod handlerMethod) {
	return true;
}
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若是是Get或Head请求调用getLastModified()获取上次更新时间

若是小于浏览器缓存更新时间则直接返回浏览器使用本地缓存

#org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter
@Override
protected long getLastModifiedInternal(HttpServletRequest request, HandlerMethod handlerMethod) {
   return -1;
}
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调用handler()方法完成过程调用(参数解析返回值解析)

#org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter
@Override
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
      throws Exception {
   return handleInternal(request, response, (HandlerMethod) handler);
}

#org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter
@Override
protected ModelAndView handleInternal(HttpServletRequest request,
		HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
	//对http协议缓存方面的请求头的处理(expire,cache-control)
	if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
		checkAndPrepare(request, response, this.cacheSecondsForSessionAttributeHandlers, true);
	}else {
		checkAndPrepare(request, response, true);
	}
	//是否使用session锁
	if (this.synchronizeOnSession) {
		HttpSession session = request.getSession(false);
		if (session != null) {
          	//获得互斥量
			Object mutex = WebUtils.getSessionMutex(session);
			synchronized (mutex) {//执行过程调用
				return invokeHandleMethod(request, response, handlerMethod);
			}
		}
	}
	//执行过程调用(参数解析 过程调用)
	return invokeHandleMethod(request, response, handlerMethod);
}
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参数解析,过程调用流程分析

//根据HandlerMethod解析参数 并完成过程调用获得一个ModelAndView
private ModelAndView invokeHandleMethod(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
  ServletWebRequest webRequest = new ServletWebRequest(request, response);
  try {
    //对@InitBinder的处理 主要是聚合了@InitBinder的全部处理方法
    WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
    //@ModelAttribute的处理
    ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
	//对HandlerMethod的装饰,主要是增长了参数解析和返回值转化的功能
    ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
    //提供对参数解析的支持
    invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
    //提供对返回值解析的支持
    invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
    //提供对@InitBinder处理的支持
    invocableMethod.setDataBinderFactory(binderFactory);
    //TODO 尚不明功能
    invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);
	
    //能够看作handler()过程的上下文
    ModelAndViewContainer mavContainer = new ModelAndViewContainer();
    mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
    modelFactory.initModel(webRequest, mavContainer, invocableMethod);
    mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);
==========================异步处理分割线=============	
	//AsyncWebRequest内部持有AsyncContext 能够经过其开启异步任务
    AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
    asyncWebRequest.setTimeout(this.asyncRequestTimeout);
	//异步处理Manager
    WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
    //设置异步执行线程池
    asyncManager.setTaskExecutor(this.taskExecutor);
    //提供对异步处理的支持
    asyncManager.setAsyncWebRequest(asyncWebRequest);
    //异步调用拦截器
    asyncManager.registerCallableInterceptors(this.callableInterceptors);
    asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);
	//若是异步处理完成
    if (asyncManager.hasConcurrentResult()) {
      //获取异步执行结果
      Object result = asyncManager.getConcurrentResult();
      mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];
      asyncManager.clearConcurrentResult();
      ...
      //替换invocableMethod(原先异步处理的方法返回值是Callable如今直接返回结果)
      invocableMethod = invocableMethod.wrapConcurrentResult(result);
    }
	//对invocableMethod进行参数解析,过程调用,返回值转化
    //并将结果存到mavContainer中
    invocableMethod.invokeAndHandle(webRequest, mavContainer);
    //若是异步处理正在执行(已经开始,还没有结束) 马上返回
    //同时DispatcherServlet也直接返回 等待AsyncContext.dispatch()调用再次进入doDispatch()方法
    if (asyncManager.isConcurrentHandlingStarted()) {
      return null;
    }
	//从mavContainer捞出结果
    return getModelAndView(mavContainer, modelFactory, webRequest);
  }
  finally {
    webRequest.requestCompleted();
  }
}
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以上是invokeHandleMethod()的完整过程

但在调用过程当中实际从异步处理分割线开始分为2种状况:

同步调用: 过程比较简单,直接进行参数解析和返回值转化就行了

invocableMethod.invokeAndHandle(webRequest, mavContainer);
return getModelAndView(mavContainer, modelFactory, webRequest);
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异步调用:

再分为两种状况:

异步处理中(已开始,还没有完成)

//AsyncWebRequest内部持有AsyncContext 能够经过其开启异步任务
AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
asyncWebRequest.setTimeout(this.asyncRequestTimeout);
//异步处理Manager
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
//设置异步执行线程池
asyncManager.setTaskExecutor(this.taskExecutor);
//提供对异步处理的支持
asyncManager.setAsyncWebRequest(asyncWebRequest);
//异步调用拦截器
asyncManager.registerCallableInterceptors(this.callableInterceptors);
asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);
//对invocableMethod进行参数解析,过程调用(调用AsyncWebRequest.startAsync()执行异步过程),返回值转化
//并将结果存到mavContainer中
invocableMethod.invokeAndHandle(webRequest, mavContainer);
//若是异步处理正在执行(已经开始,还没有结束) 马上返回
//同时DispatcherServlet也直接返回 
return null;

#org.springframework.web.servlet.DispatcherServlet
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
  ...
  mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
  if (asyncManager.isConcurrentHandlingStarted()) {
    return;
  }
  ...
}
//等待AsyncWebRequest.dispatch()被调用 而后再次进入doDispatch()方法

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异步执行完成,再次进入doDispatch()流程

//AsyncWebRequest内部持有AsyncContext 能够经过其开启异步任务
AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
asyncWebRequest.setTimeout(this.asyncRequestTimeout);
//异步处理Manager
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
//设置异步执行线程池
asyncManager.setTaskExecutor(this.taskExecutor);
//提供对异步处理的支持
asyncManager.setAsyncWebRequest(asyncWebRequest);
//异步调用拦截器
asyncManager.registerCallableInterceptors(this.callableInterceptors);
asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);
//异步处理完成 获取异步执行结果
Object result = asyncManager.getConcurrentResult();
mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];
asyncManager.clearConcurrentResult();
//替换invocableMethod(原先异步处理的方法返回值是Callable如今直接返回结果)
invocableMethod = invocableMethod.wrapConcurrentResult(result);
//对invocableMethod进行参数解析,过程调用,返回值转化
//并将结果存到mavContainer中
invocableMethod.invokeAndHandle(webRequest, mavContainer);
//从mavContainer捞出结果
return getModelAndView(mavContainer, modelFactory, webRequest);
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ServletInvocableHandlerMethod

先看一下ServletInvocableHandlerMethod是个什么东东

HandlerMethod:保存了处理过程方法

InvocableHandlerMethod: 对HandlerMethod的装饰,增长了参数解析的功能

ServletInvocableHandlerMethod:对HandlerMethod的装饰,增长了返回值转化的功能

同步流程

invocableMethod.invokeAndHandle(webRequest, mavContainer);

#org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod
public void invokeAndHandle(ServletWebRequest webRequest,
                    ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception {
  // 1.1 参数解析 并完成过程调用
  Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
  setResponseStatus(webRequest);
  ...
    try {
      //1.2 使用returnValueHandlers对返回结果进行处理 讲结果塞到mavContainer中 过程相似参数解析
      this.returnValueHandlers.handleReturnValue(
        returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
    }
}
#org.springframework.web.method.support.InvocableHandlerMethod
public Object invokeForRequest(NativeWebRequest request, ModelAndViewContainer mavContainer,
                                       Object... providedArgs) throws Exception {
  //1.1.1 参数解析并获得绑定的结果
  Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
  ...
    //1.1.2 反射完成过程调用 
    Object returnValue = doInvoke(args);
  ...
    return returnValue;
}
private Object[] getMethodArgumentValues(NativeWebRequest request, ModelAndViewContainer mavContainer,
                                         Object... providedArgs) throws Exception {
  //参数信息
  MethodParameter[] parameters = getMethodParameters();
  Object[] args = new Object[parameters.length];
  for (int i = 0; i < parameters.length; i++) {
    //调用HandlerMethodArgumentResolver#supportsParameter判断是否支持该参数的解析
    if (this.argumentResolvers.supportsParameter(parameter)) {
      try {
        //调用HandlerMethodArgumentResolver#resolveArgument进行解析
        args[i] = this.argumentResolvers.resolveArgument(
          parameter, mavContainer, request, this.dataBinderFactory);
        continue;
      }
      ...
    }
    ...
  }
  return args;
}
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包装ModelAndView getModelAndView(mavContainer, modelFactory, webRequest);

//从mavContainer取出结果 包装成ModelAndView
private ModelAndView getModelAndView(ModelAndViewContainer mavContainer, ModelFactory modelFactory, NativeWebRequest webRequest) throws Exception {
  modelFactory.updateModel(webRequest, mavContainer);
  if (mavContainer.isRequestHandled()) {
    return null;
  }
  ModelMap model = mavContainer.getModel();
  ModelAndView mav = new ModelAndView(mavContainer.getViewName(), model);
  if (!mavContainer.isViewReference()) {
    mav.setView((View) mavContainer.getView());
  }
  //若是是redirect请求
  if (model instanceof RedirectAttributes) {
    Map<String, ?> flashAttributes = ((RedirectAttributes) model).getFlashAttributes();
    HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);
    RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes);
  }
  return mav;
}
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到此 HandlerAdapter.handler的调用过程算分析完了

@InitBinder的处理

WebDataBinder:数据(对象属性)绑定器,用于对对象的属性进行转化(Formatter)和校验(Validator)

InitBinder: @InitBinder注解用于在参数解析前初始化WebDataBinder.简单来讲就是能够对WebDataBinder增长Validator和属性转化器Formatter

@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface InitBinder {
	//在哪些属性上发生做用
	String[] value() default {};
}
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示例

@InitBinder
protected void initBinder(WebDataBinder binder) {
 //添加自定义Data类型Formatter
  SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
  dateFormat.setLenient(false);
  binder.registerCustomEditor(Date.class, new CustomDateEditor(dateFormat, false));
}

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@InitBinder方法分为两种:

全局@InitBinder:定义在注解有@ControllerAdvices的类中,装载发生在HandlerAdapter初始化调用initControllerAdviceCache()过程当中(见上文初始化过程分析)

局部@InitBinder:定义在注解有@Controller的类中,装载发生在HandlerAdapter.handler()调用getDataBinderFactory()过程当中

private WebDataBinderFactory getDataBinderFactory(HandlerMethod handlerMethod) throws Exception {
  //获取处理方法所在的类
  Class<?> handlerType = handlerMethod.getBeanType();
  //从保存的全局缓存中找属于该类的局部@InitBinder方法
  Set<Method> methods = this.initBinderCache.get(handlerType);
  if (methods == null) {//若是没找到 说明该类不是一个@ControllerAdvices注解的类(只有@Controller没有@ControllerAdvices)
    //获得该类中全部@InitBinder注解的方法
    methods = MethodIntrospector.selectMethods(handlerType, INIT_BINDER_METHODS);
    //将局部@InitBinder方法缓存到initBinderCache中
    this.initBinderCache.put(handlerType, methods);
  }
  List<InvocableHandlerMethod> initBinderMethods = new ArrayList<InvocableHandlerMethod>();
  //将全局@InitBinder方法包装成InvocableHandlerMethod,添加到initBinderMethods
  for (Entry<ControllerAdviceBean, Set<Method>> entry : this.initBinderAdviceCache.entrySet()) {
    if (entry.getKey().isApplicableToBeanType(handlerType)) {
      Object bean = entry.getKey().resolveBean();
      for (Method method : entry.getValue()) {
        initBinderMethods.add(createInitBinderMethod(bean, method));
      }
    }
  }
  //将局部@InitBinder方法包装成InvocableHandlerMethod,添加到initBinderMethods
  for (Method method : methods) {
    Object bean = handlerMethod.getBean();
    initBinderMethods.add(createInitBinderMethod(bean, method));
  }
  //使用initBinderMethods对象(局部+全局),包装成WebDataBinderFactory对象
  return createDataBinderFactory(initBinderMethods);
}
protected InitBinderDataBinderFactory createDataBinderFactory(List<InvocableHandlerMethod> binderMethods) throws Exception {
  return new ServletRequestDataBinderFactory(binderMethods, getWebBindingInitializer());
}

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看完了了@InitBinder的装载过程,来看下@InitBinder方法是怎样被处理的

处理过程

this.argumentResolvers.resolveArgument(
          parameter, mavContainer, request, this.dataBinderFactory);
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能够看到在使用argumentResolvers.resolveArgument()进行参数解析时将dataBinderFactory做为参数传递了过去

分别来看RequestParamMapMethodArgumentResolver,RequestResponseBodyMethodProcessor,ModelAttributeMethodProcessor三个参数解析器是如何处理@InitBinder方法的

RequestParamMapMethodArgumentResolver

@Override
	public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
      // 彻底没使用binderFactory
      ...
	}
}
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由于说过@InitBinder是用来初始化WebDataBinder的,而RequestParamMapMethodArgumentResolver是处理表单属性的(不是对象),因此彻底没用

RequestResponseBodyMethodProcessor

@Override
public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
  parameter = parameter.nestedIfOptional();
 //使用binderFactory建立对象解析器
  WebDataBinder binder = binderFactory.createBinder(webRequest, arg, name);
  if (arg != null) {
    //使用对象解析进行参数校验
    validateIfApplicable(binder, parameter);
    //若是参数校验异常,且目标方法参数列表中没有BindingResult类型参数,则直接抛出参数解析异常
    if (binder.getBindingResult().hasErrors() && isBindExceptionRequired(binder, parameter)) 	{
    throw new MethodArgumentNotValidException(parameter, binder.getBindingResult());
    }
  }
  //将参数解析结果存到mavContainer上下文中
  mavContainer.addAttribute(BindingResult.MODEL_KEY_PREFIX + name, binder.getBindingResult());
  return adaptArgumentIfNecessary(arg, parameter);
}

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由于RequestResponseBodyMethodProcessor将属性绑定委托给了json解析器,因此这里WebDataBinder只负责参数校验

ModelAttributeMethodProcessor

@Override
public final Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {

  String name = ModelFactory.getNameForParameter(parameter);
  Object attribute = (mavContainer.containsAttribute(name) ? mavContainer.getModel().get(name) :
                      createAttribute(name, parameter, binderFactory, webRequest));
	...
  WebDataBinder binder = binderFactory.createBinder(webRequest, attribute, name);
  if (binder.getTarget() != null) {
    //使用binder进行属性绑定
    if (!mavContainer.isBindingDisabled(name)) {
      bindRequestParameters(binder, webRequest);
    }
    //使用binder进行属性校验
    validateIfApplicable(binder, parameter);
    if (binder.getBindingResult().hasErrors() && 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.convertIfNecessary(binder.getTarget(), parameter.getParameterType(), parameter);
}
protected Object createAttribute(String attributeName, MethodParameter methodParam, WebDataBinderFactory binderFactory, NativeWebRequest request) throws Exception {
  return BeanUtils.instantiateClass(methodParam.getParameterType());
}
protected void bindRequestParameters(WebDataBinder binder, NativeWebRequest request) {
  ((WebRequestDataBinder) binder).bind(request);
}
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使用WebDataBinder进行了属性绑定和属性校验