controller

接收参数   用 HttpServletRequest 代替 @RequestParam()  接收参数

 

picFile 前台 传文件的参数名字  ,   这样 前段 传 null  就可以  不必须 存文件了

 MultipartFile picFile = null;
            boolean isMultipart = ServletFileUpload.isMultipartContent(request);
            if (isMultipart){
                MultipartHttpServletRequest multipartRequest = WebUtils.getNativeRequest(request, MultipartHttpServletRequest.class);
                picFile = multipartRequest.getFile("picFile");
            }

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https://blog.csdn.net/zhaofuwu/article/details/52694487

https://blog.csdn.net/m0_38004838/article/details/78286067

 springMVC的   https://blog.csdn.net/chenchunlin526/article/details/70945877