asp.net文件下载

      protected void btn_Down(object sender, EventArgs e)
        {
            string filePath = Server.MapPath("/TradeLog/" + txtDate.Text.Trim());
            if (!downBeforeValidation(filePath))
                return;
            dlZipDir(filePath, txtDate.Text);
        }    

       /// <summary>
        /// 下载前验证
        /// </summary>
        /// <param name="filePath">文件路径</param>
        /// <returns></returns>
        private bool downBeforeValidation(string filePath)
        {
            //判断密码是否正确
            string downPassWord = WebConfigurationManager.AppSettings["downPassWord"];
            if (string.IsNullOrEmpty(txtPassWord.Text) || txtPassWord.Text.Trim() != downPassWord)
            {
                Response.Write("<script>alert('密码错误或为空')</script>");
                return false;
            }
            //判断文件是否存在

            if (!Directory.Exists(filePath))
            {
                Response.Write("<script>alert('目录不存在')</script>");
                return false;
            }
            return true;
        }

      /// <summary>
        /// 全部变量
        /// </summary>
        ZipOutputStream zos = null;
        String strBaseDir = "";
        /// <summary>
        /// 下载文件
        /// </summary>
        /// <param name="strPath">路径</param>
        /// <param name="strFileName">下载后默认显示文件名称</param>
        void dlZipDir(string strPath, string strFileName)
        {
            MemoryStream ms = null;
            Response.ContentType = "application/octet-stream";
            strFileName = HttpUtility.UrlEncode(strFileName).Replace('+', ' ');
            Response.AddHeader("Content-Disposition", "attachment;   filename=" + strFileName + ".zip");
            ms = new MemoryStream();
            zos = new ZipOutputStream(ms);
            strBaseDir = strPath + "\\";
            addZipEntry(strBaseDir);
            zos.Finish();
            zos.Close();
            Response.Clear();
            Response.BinaryWrite(ms.ToArray());
            Response.End();
        }

     /// <summary>
        /// 生成压缩文件
        /// </summary>
        /// <param name="PathStr"></param>
        void addZipEntry(string PathStr)
        {
            DirectoryInfo di = new DirectoryInfo(PathStr);
            foreach (DirectoryInfo item in di.GetDirectories())
            {
                addZipEntry(item.FullName);
            }
            foreach (FileInfo item in di.GetFiles())
            {
                FileStream fs = File.OpenRead(item.FullName);
                byte[] buffer = new byte[fs.Length];
                fs.Read(buffer, 0, buffer.Length);
                string strEntryName = item.FullName.Replace(strBaseDir, "");
                ZipEntry entry = new ZipEntry(strEntryName);
                zos.PutNextEntry(entry);
                zos.Write(buffer, 0, buffer.Length);
                fs.Close();
            }
        }