controller

接收引數   用 HttpServletRequest 代替 @RequestParam()  接收引數

picFile 前臺 傳檔案的引數名字  ,   這樣 前段 傳 null  就可以  不必須 存檔案了

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

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