springMVC(二)： @RequestBody @ResponseBody 注解实现分析

一、继承结构

@RequestBody、@ResponseBody的处理器：RequestResponseBodyMethodProcessor

@ModelAttribute处理器： ModelAttributeMethodProcessor

HttpEntity处理器： HttpEntityMethodProcessor

参数值解析器： HandlerMethodArgumentResolver

返回值处理器： HandlerMethodReturnValueHandler

使用HttpMessageConverter 转换方法参数： AbstractMessageConverterMethodArgumentResolver

二、 处理过程

1. RequestResponseBodyMethodProcessor的resolveArgument过程

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

　　　　 //返回@RequestBody需要的参数, Spring使用我们自定义的RequestBodyAdvice, ResponseBodyAdvice发生在这里
        Object arg = readWithMessageConverters(webRequest, parameter, parameter.getGenericParameterType());
        String name = Conventions.getVariableNameForParameter(parameter);

　　　　　//输入参数转换成Java对象发生在这里，后面有专门的文章讲解，注意：每次请求绑定的对象的重新生成的
        WebDataBinder binder = binderFactory.createBinder(webRequest, arg, name);
        if (arg != null) {
            validateIfApplicable(binder, parameter);
            if (binder.getBindingResult().hasErrors() && isBindExceptionRequired(binder, parameter)) {
                throw new MethodArgumentNotValidException(parameter, binder.getBindingResult());
            }
        }
        mavContainer.addAttribute(BindingResult.MODEL_KEY_PREFIX + name, binder.getBindingResult());

        return arg;
    }

    @Override
    protected <T> Object readWithMessageConverters(NativeWebRequest webRequest, MethodParameter methodParam,
            Type paramType) throws IOException, HttpMediaTypeNotSupportedException, HttpMessageNotReadableException {

        HttpServletRequest servletRequest = webRequest.getNativeRequest(HttpServletRequest.class);
        ServletServerHttpRequest inputMessage = new ServletServerHttpRequest(servletRequest);

　　　　　//调用父类的readWithMessageCoverters()方法
        Object arg = readWithMessageConverters(inputMessage, methodParam, paramType);  
        if (arg == null) {
            if (methodParam.getParameterAnnotation(RequestBody.class).required()) {
                throw new HttpMessageNotReadableException("Required request body is missing: " +
                        methodParam.getMethod().toGenericString());
            }
        }
        return arg;
    }