protected void Button3_Click(object sender, EventArgs e)

        {

            string fileName = "asd.txt";//客户端保存的文件名

            string filePath = "E://aaa.txt"; //Server.MapPath("DownLoad/aaa.txt");//路径

            FileInfo fileInfo = new FileInfo(filePath);

            Response.Clear();

            Response.ClearContent();

            Response.ClearHeaders();

            Response.AddHeader("Content-Disposition", "attachment;filename=" + fileName);

            Response.AddHeader("Content-Length", fileInfo.Length.ToString());

            Response.AddHeader("Content-Transfer-Encoding", "binary");

            Response.ContentType = "application/octet-stream";

            Response.ContentEncoding = System.Text.Encoding.GetEncoding("gb2312");

            Response.WriteFile(fileInfo.FullName);

            Response.Flush();

            Response.End();

        }

  FileStream fs = null;

                   try

                   {

                       String fileName = ViewState["Attchment"].ToString();

                       String filePath = Server.MapPath(@"~/UpLoad/Attchment/" + fileName);

                       //以字符流的形式下载

                       fs = new FileStream(filePath, FileMode.Open);

                       byte[] bytes = new byte[(int)fs.Length];

                       fs.Read(bytes, 0, bytes.Length);

      &nbs