spring mvc controller 方法处理参数的过程

    @ResponseBody
    @RequestMapping(value = "/trans", method = RequestMethod.POST,produces = "application/json;charset=UTF-8")
    public String trans(@RequestBody Qrs req){
　　　　　　req.setUuid(xxx);
　　　　　　MDC.put("uuid",xxx); //MDC 是logback的一个设置公共参数的类。 在logback.xml 配置pattern 使用 %X{uuid}即可打印唯一标识了

}

public class MyFilter implements Filter { 

　　@Override 
　　protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response) throws ServletException { 
　　　　request.setAttribute("uuid",xxx);　　
　　　　....
 }
}

HandlerMethodArgumentResolverComposite 类： 
1. 判断是否有能处理该参数的resolver 
public boolean supportsParameter(MethodParameter parameter) {
        return this.getArgumentResolver(parameter) != null;
    }

2. 如果有 ，存入argumentResolverCache(当有相同参数类型是，直接去该resolver)
private HandlerMethodArgumentResolver getArgumentResolver(MethodParameter parameter) {
        HandlerMethodArgumentResolver result = (HandlerMethodArgumentResolver)this.argumentResolverCache.get(parameter);
        if (result == null) {
            Iterator var3 = this.argumentResolvers.iterator();

            while(var3.hasNext()) {
                HandlerMethodArgumentResolver methodArgumentResolver = (HandlerMethodArgumentResolver)var3.next();
                if (this.logger.isTraceEnabled()) {
                    this.logger.trace("Testing if argument resolver [" + methodArgumentResolver + "] supports [" + parameter.getGenericParameterType() + "]");
                }

                if (methodArgumentResolver.supportsParameter(parameter)) {
                    result = methodArgumentResolver;
                    this.argumentResolverCache.put(parameter, methodArgumentResolver);
                    break;
                }
            }
        }

        return result;
    }

3. 调用resolveArgument方法，实际是调用上一步找到resolver. 
public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
        HandlerMethodArgumentResolver resolver = this.getArgumentResolver(parameter);
        Assert.notNull(resolver, "Unknown parameter type [" + parameter.getParameterType().getName() + "]");
        return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory);
    }

RequestResponseBodyMethodProcessor 类：
@Override
    public boolean supportsParameter(MethodParameter parameter) {
        return parameter.hasParameterAnnotation(RequestBody.class);//所以支持@RequestBody 注解的参数
    }

2. 处理参数，主要readWithMessageConverters
@Override
    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
            NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {

        Object arg = readWithMessageConverters(webRequest, parameter, parameter.getGenericParameterType());
        String name = Conventions.getVariableNameForParameter(parameter);
        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;
    }
3. 该类继承AbstractMessageConverterMethodArgumentResolver，重要代码是
this.messageConverters 这个循环，找到相应转换类，跟踪代码找到的是MappingJackson2HttpMessageConverter
@SuppressWarnings("unchecked")
    protected <T> Object readWithMessageConverters(HttpInputMessage inputMessage,
            MethodParameter methodParam, Type targetType) throws IOException, HttpMediaTypeNotSupportedException {

        MediaType contentType;
        try {
            contentType = inputMessage.getHeaders().getContentType();
        }
        catch (InvalidMediaTypeException ex) {
            throw new HttpMediaTypeNotSupportedException(ex.getMessage());
        }
        if (contentType == null) {
            contentType = MediaType.APPLICATION_OCTET_STREAM;
        }

        Class<?> contextClass = methodParam.getContainingClass();
        Class<T> targetClass = (Class<T>)
                ResolvableType.forMethodParameter(methodParam, targetType).resolve(Object.class);

        for (HttpMessageConverter<?> converter : this.messageConverters) {
            if (converter instanceof GenericHttpMessageConverter) {
                GenericHttpMessageConverter<?> genericConverter = (GenericHttpMessageConverter<?>) converter;
                if (genericConverter.canRead(targetType, contextClass, contentType)) {
                    if (logger.isDebugEnabled()) {
                        logger.debug("Reading [" + targetType + "] as \"" +
                                contentType + "\" using [" + converter + "]");
                    }
                    return genericConverter.read(targetType, contextClass, inputMessage);
                }
            }
            if (converter.canRead(targetClass, contentType)) {
                if (logger.isDebugEnabled()) {
                    logger.debug("Reading [" + targetClass.getName() + "] as \"" +
                            contentType + "\" using [" + converter + "]");
                }
                return ((HttpMessageConverter<T>) converter).read(targetClass, inputMessage);
            }
        }

        throw new HttpMediaTypeNotSupportedException(contentType, this.allSupportedMediaTypes);
    }

4. 对应 AbstractJackson2HttpMessageConverter.read 方法，读取请求流中的数据，
后面估计是利用反射赋值，没有再深入了解了。
private Object readJavaType(JavaType javaType, HttpInputMessage inputMessage) {
        try {
            return this.objectMapper.readValue(inputMessage.getBody(), javaType);
        } catch (IOException var4) {
            throw new HttpMessageNotReadableException("Could not read JSON: " + var4.getMessage(), var4);
        }
    }