C#實現下載功能

protected void Button4_Click(object sender, EventArgs e)
        {
            string fileName = "aaa.txt";//用戶端儲存的檔案名稱
            string filePath = Server.MapPath("DownLoad/aaa.txt");//路徑
            //以字元流的形式下載檔案
            FileStream fs = new FileStream(filePath, FileMode.Open);
            byte[] bytes = new byte[(int)fs.Length];
            fs.Read(bytes, 0, bytes.Length);
            fs.Close();
            Response.ContentType = "application/octet-stream";
            //通知瀏覽器下載檔案而不是開啟
            Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(fileName, System.Text.Encoding.UTF8));
            Response.BinaryWrite(bytes);
            Response.Flush();
            Response.End();
        }