我想用spring将File转换为multipartfile。我做了这个:Filein;MultipartFilefile=null;in=newFile("C:...fileondisk");intsize=(int)in.length();DiskFileItemfileItem=newDiskFileItem("file","application/vnd.ms-excel",false,nomefile,size,in.getAbsoluteFile());file=newCommonsMultipartFile(fileItem);但收到此异常:threwexception[