asp.Net実装ファイルダウンロード

protected void Button1_Click(object sender, EventArgs e)   
 {       
 this.DownLoadFile("  .txt");    
}    
//       
 private void DownLoadFile(string fileName)  
  {         
 string filePath = Server.MapPath(".") + "\\" + fileName;       
 if (File.Exists(filePath))       
 {           
 FileInfo file = new FileInfo(filePath);           
 Response.ContentEncoding = System.Text.Encoding.GetEncoding("UTF-8"); //                  
Response.AddHeader("Content-Disposition", "attachment; filename=" + Server.UrlEncode(file.Name)); //                         

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

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

      Response.WriteFile(file.FullName);    

        
Response.End();       
 }   
 }