controller

接收參數 用 HttpServletRequest 代替 @RequestParam() 接收參數

picFile 前臺 傳文件的參數名字 , 這樣 前段 傳 null 就可以 不必須 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");
            }

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

MultipartFile 動態決定是否上傳文件,解決不上傳文件報錯