用Filter 改造http上传信息

1. 写一个Filter (XxxFilter)继承 OncePerRequestFilter

        doFilter方法的第一个参数HttpServletRequest需要自定类重写（如：HttpRequestWrapper继承ContentCachingRequestWrapper）

2. post 请求

        1. XxxFilter

        2. ServletRequestWrapper:167-getParameterMap()

Request (org.apache.catalina.connector.Request):1143-getParameterMap()

       getParameterNames()一parseParameters():读取body等参数然后存储在此类parameterMap中

        3.解折RequestBody

RequestResponseBodyMethodProcessor这个类用来解析@RequestBody和@ResponseBody返回值解析

resolveArgument

        readwithMessageConverters

        readwithMessageConvertersmessage                                
        new EmptyBodyCheckingHttpInputMessage(inputMessage);
                InputStream inputStream = inputMessage.getBody();

                XxxFilter.getInputStream()--Request.getInputStream()     

        4. @RequestBody与@RequestParam

                @RequestBody对应postman前端上送的raw类型，由Request.getInputStream()获得；      

                @RequestParam对应postman前端上送的from-data或x-www-form-urlencoded类型，                                           由Request中的parameterMap中获得；

 Request.getInputStream()中注意     

        1.3241: readPostBody(formData,len)I=len  读取body内容

        2.3185:     if (usingInputstream II usingReader){
                                 success true; 
                                 return;

                                }

如果调用getInputstream()或getReader()则会usingInputstream或usingReadert改为txue,不在调用3241行的代码读取body内容, ——不可再HttpRequestWrapper的构造函数中调用getInputstream()或getReader()方法