随便写一个demo:

    @RequestMapping("/car/{id}")public Map<String, Object> getCar(@PathVariable("id") Integer id,@RequestParam("type") String type,@RequestParam("hobby") List<String> hobby){Map<String, Object> map = new HashMap<>();map.put("id",id);map.put("type",type);map.put("hobby", hobby);return map;}

之前说过通过获取到的mapperHandler中以及找到了控制器以及具体的方法，接下来就需要来处理方法中的各种类型的参数，也就是需要用的SpringMVC中提供的HandlerAdapter。

一、HandlerAdapter

该接口主要就两个方法，一个supports用来判断是否支持这类适配器，如果支持就进行处理（handle方法）。

SpringMVC给我们创建了四种Adapter ：

0—针对含有RequestMapping注解的处理器

......

1.1 RequestMappingHandlerAdapter

获取到第一个适配器RequestMappingHandlerAdapter，调用其supports方法，判断是否支持请求。

supports()

最后就获取到了适合当前请求的适配器了。

1.2 执行获取到的适配器

在上一步中获取到的适配器在这里进行处理。

在该方法内部会唤醒控制器的方法

可以看到无论是否满足if条件，都会执行invokeHandlerMethod这个方法

 @Nullableprotected ModelAndView invokeHandlerMethod(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {ServletWebRequest webRequest = new ServletWebRequest(request, response);ModelAndView var15;try {WebDataBinderFactory binderFactory = this.getDataBinderFactory(handlerMethod);ModelFactory modelFactory = this.getModelFactory(handlerMethod, binderFactory);ServletInvocableHandlerMethod invocableMethod = this.createInvocableHandlerMethod(handlerMethod);if (this.argumentResolvers != null) {invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);}if (this.returnValueHandlers != null) {invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);}invocableMethod.setDataBinderFactory(binderFactory);invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);ModelAndViewContainer mavContainer = new ModelAndViewContainer();mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));modelFactory.initModel(webRequest, mavContainer, invocableMethod);mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);asyncWebRequest.setTimeout(this.asyncRequestTimeout);WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);asyncManager.setTaskExecutor(this.taskExecutor);asyncManager.setAsyncWebRequest(asyncWebRequest);asyncManager.registerCallableInterceptors(this.callableInterceptors);asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);Object result;if (asyncManager.hasConcurrentResult()) {result = asyncManager.getConcurrentResult();mavContainer = (ModelAndViewContainer)asyncManager.getConcurrentResultContext()[0];asyncManager.clearConcurrentResult();LogFormatUtils.traceDebug(this.logger, (traceOn) -> {String formatted = LogFormatUtils.formatValue(result, !traceOn);return "Resume with async result [" + formatted + "]";});invocableMethod = invocableMethod.wrapConcurrentResult(result);}invocableMethod.invokeAndHandle(webRequest, mavContainer, new Object[0]);if (asyncManager.isConcurrentHandlingStarted()) {result = null;return (ModelAndView)result;}var15 = this.getModelAndView(mavContainer, modelFactory, webRequest);} finally {webRequest.requestCompleted();}return var15;}

在这个方法内部，注意到：

argumentResolvers参数解析器（SpringMVC提供的）。

里面共有27个参数解析器，每一个参数和其注解都会进行一一匹配。

和上面的HandlerAdapter一样的结构，先判断然后去执行。

准备工作完成之后开始给参数赋值，具体的赋值过程如下：

    public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception {Object returnValue = this.invokeForRequest(webRequest, mavContainer, providedArgs);this.setResponseStatus(webRequest);if (returnValue == null) {if (this.isRequestNotModified(webRequest) || this.getResponseStatus() != null || mavContainer.isRequestHandled()) {this.disableContentCachingIfNecessary(webRequest);mavContainer.setRequestHandled(true);return;}} else if (StringUtils.hasText(this.getResponseStatusReason())) {mavContainer.setRequestHandled(true);return;}mavContainer.setRequestHandled(false);Assert.state(this.returnValueHandlers != null, "No return value handlers");try {this.returnValueHandlers.handleReturnValue(returnValue, this.getReturnValueType(returnValue), mavContainer, webRequest);} catch (Exception var6) {if (logger.isTraceEnabled()) {logger.trace(this.formatErrorForReturnValue(returnValue), var6);}throw var6;}}

其中这一步是真正的执行目标方法，里面有doInvoke方法，利用反射执行控制器的方法

执行完之后获取到了请求方法中的参数并且也都赋值了。

所以看看invokeForRequest方法内部是如何获取参数并赋值的

1.3 获取方法中的参数并赋值

    @Nullablepublic Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception {Object[] args = this.getMethodArgumentValues(request, mavContainer, providedArgs);if (logger.isTraceEnabled()) {logger.trace("Arguments: " + Arrays.toString(args));}return this.doInvoke(args);}

该方法内部调用了getMethodArgumentValues方法，说明是通过这个方法来获取参数值的：

protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception {MethodParameter[] parameters = this.getMethodParameters();if (ObjectUtils.isEmpty(parameters)) {return EMPTY_ARGS;} else {Object[] args = new Object[parameters.length];for(int i = 0; i < parameters.length; ++i) {MethodParameter parameter = parameters[i];parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);args[i] = findProvidedArgument(parameter, providedArgs);if (args[i] == null) {if (!this.resolvers.supportsParameter(parameter)) {throw new IllegalStateException(formatArgumentError(parameter, "No suitable resolver"));}try {args[i] = this.resolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory);} catch (Exception var10) {if (logger.isDebugEnabled()) {String exMsg = var10.getMessage();if (exMsg != null && !exMsg.contains(parameter.getExecutable().toGenericString())) {logger.debug(formatArgumentError(parameter, exMsg));}}throw var10;}}}return args;}}

第一步获取到的parameters

内部的基本过程就是：在获取到的parameters集合中的参数一个一个进行迭代然后选择合适的解析器，并且根据url中的路径来进行赋值，即可！

第二类：自定义对象参数

简单Demo：

HTML页面表单：

    <form action="/getPerson" method="get">姓名:<input name="userName" value="zhangsan"><br/>年龄：<input name="age" value="25"><br/>宠物名：<input name="pet.name" value="dahua"><br/>宠物年龄<input name="pet.age" value="2"><br/><input type="submit" value="保存"></form>

Controller：

    @RequestMapping("/getPerson")public Person getPerson(Person person){return person;}

结果：

现在问题是如何将表单中提交的数据封装成了一个Person对象的？

再一次说到getMethodArgumentValues中

protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception {......try {args[i] = this.resolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory);} ......}

这里的大概逻辑就是先是获取到了控制器方法中的参数，初步判断是否为空（没赋值的时候肯定为空），然后再try里头有这个方法

也就是一个一个给参数赋值的过程。最终到达参数赋值的方法体中：

    @Nullablepublic final Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer, NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {Assert.state(mavContainer != null, "ModelAttributeMethodProcessor requires ModelAndViewContainer");Assert.state(binderFactory != null, "ModelAttributeMethodProcessor requires WebDataBinderFactory");String name = ModelFactory.getNameForParameter(parameter);ModelAttribute ann = (ModelAttribute)parameter.getParameterAnnotation(ModelAttribute.class);if (ann != null) {mavContainer.setBinding(name, ann.binding());}Object attribute = null;BindingResult bindingResult = null;if (mavContainer.containsAttribute(name)) {attribute = mavContainer.getModel().get(name);} else {try {attribute = this.createAttribute(name, parameter, binderFactory, webRequest);} catch (BindException var10) {if (this.isBindExceptionRequired(parameter)) {throw var10;}if (parameter.getParameterType() == Optional.class) {attribute = Optional.empty();} else {attribute = var10.getTarget();}bindingResult = var10.getBindingResult();}}if (bindingResult == null) {WebDataBinder binder = binderFactory.createBinder(webRequest, attribute, name);if (binder.getTarget() != null) {if (!mavContainer.isBindingDisabled(name)) {this.bindRequestParameters(binder, webRequest);}this.validateIfApplicable(binder, parameter);if (binder.getBindingResult().hasErrors() && this.isBindExceptionRequired(binder, parameter)) {throw new BindException(binder.getBindingResult());}}if (!parameter.getParameterType().isInstance(attribute)) {attribute = binder.convertIfNecessary(binder.getTarget(), parameter.getParameterType(), parameter);}bindingResult = binder.getBindingResult();}Map<String, Object> bindingResultModel = bindingResult.getModel();mavContainer.removeAttributes(bindingResultModel);mavContainer.addAllAttributes(bindingResultModel);return attribute;}