java.lang.IllegalArgumentException: Files' name is invalid or does not exist

Question

<%@page import="com.xilin.zhaoshengsystem.dao.IGoods"%>
<%@page import="com.xilin.zhaoshengsystem.daoImpl.GoodsImpl"%>
<%@page import="com.xilin.zhaoshengsystem.pojo.Goods"%>
<%@ page language="java" import="java.util.*,com.jspsmart.upload.*" pageEncoding="gbk"%>
<%
  String path = request.getContextPath();
  String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
    request.setCharacterEncoding("gbk");
    SmartUpload su=new SmartUpload();
su.initialize(pageContext);
com.jspsmart.upload.File file=null;
String allowed="jpg,png,rar,JPG,gif,doc";
String denied="jsp,asp,php,html,bat,exe,htm,aspx";
com.jspsmart.upload.Request req=null;
int file_size=10*1024*1024;
String exceptionMsg=null;
String paths="";
String filepath=null;
try{
       su.setAllowedFilesList(allowed);
       su.setDeniedFilesList(denied);
       su.setMaxFileSize(file_size);
       su.upload();
       file=su.getFiles().getFile(0);
       if(!file.isMissing())
       {
           filepath="/upload/";
           filepath+=file.getFileName();
           System.out.println(filepath);
           paths=filepath;
           file.saveAs(filepath, SmartUpload.SAVE_VIRTUAL);
           
       }
       
   }
   catch (Exception e){
      exceptionMsg = e.getMessage();
  e.printStackTrace();
   }