/// <summary>
  /// 测试是否可以成功连接FTP和判断文件是否存在
  /// </summary>
  /// <param name="ftpServerFilePath">FTP上文件地址</param>
  /// <param name="ftpUserId">FTP登陆用户名</param>
  /// <param name="ftpPwd">FTP登陆密码</param>
  /// <param name="errorMsg">返回错误消息</param>
  /// <returns></returns>
  private bool IsCanConnectFtp(string ftpServerFilePath, string ftpUserId, string ftpPwd, out string errorMsg)
  {
   bool flag = true;
   FtpWebResponse ftpResponse = null;
   FtpWebRequest ftpRequest = null;
   errorMsg = string.Empty;
   try
   {
    ftpRequest = (FtpWebRequest)FtpWebRequest.Create(new Uri("ftp://" + ftpServerFilePath));
    ftpRequest.Method = WebRequestMethods.Ftp.ListDirectory;
    ftpRequest.Timeout = 2 * 1000;//超时时间设置为2秒。
    ftpRequest.Credentials = new NetworkCredential(ftpUserId, ftpPwd);
    ftpResponse = (FtpWebResponse)ftpRequest.GetResponse();
   }
   catch (WebException exception)
   {
    ftpResponse = (FtpWebResponse)exception.Response;
    switch (ftpResponse.StatusCode)
    {
     case FtpStatusCode.ActionNotTakenFileUnavailable:
      errorMsg = "下载的文件不存在";
      break;
     case FtpStatusCode.ActionNotTakenFileUnavailableOrBusy:
      errorMsg = "下载的文件正在使用,请稍后再试";
      break;
     default:
      errorMsg = "发生未知错误";
      break;
    }
    flag = false;
   }
   catch
   {
    errorMsg = "网络连接发生错误,请稍后再试";
    flag = true;
   }
   finally
   {
    if (ftpResponse != null)
    {
     ftpResponse.Close();
    }
   }
   return flag;
  }

 ftpRequest = (FtpWebRequest)FtpWebRequest.Create(new Uri("ftp://" + ftpServerFilePath.Replace("\\","/")));

 /// <summary>
  /// 测试是否可以成功连接FTP和判断文件是否存在
  /// </summary>
  /// <param name="ftpServerFilePath">FTP上文件地址</param>
  /// <param name="ftpUserId">FTP登陆用户名</param>
  /// <param name="ftpPwd">FTP登陆密码</param>
  /// <param name="errorMsg">返回错误消息</param>
  /// <returns></returns>
  private bool IsCanConnectFtp(string ftpServerFilePath, string ftpUserId, string ftpPwd, out string errorMsg)
  {
   bool flag = true;
   FtpWebResponse ftpResponse = null;
   FtpWebRequest ftpRequest = null;
   errorMsg = string.Empty;
   try
   {
    ftpRequest = (FtpWebRequest)FtpWebRequest.Create(new Uri("ftp://" + ftpServerFilePath.Replace("\\","/")));
    ftpRequest.Method = WebRequestMethods.Ftp.ListDirectory;
    ftpRequest.Timeout = 2 * 1000;//超时时间设置为2秒。
    ftpRequest.Credentials = new NetworkCredential(ftpUserId, ftpPwd);
    ftpResponse = (FtpWebResponse)ftpRequest.GetResponse();
   }
   catch (WebException exception)
   {
    ftpResponse = (FtpWebResponse)exception.Response;
    switch (ftpResponse.StatusCode)
    {
     case FtpStatusCode.ActionNotTakenFileUnavailable:
      errorMsg = "下载的文件不存在";
      break;
     case FtpStatusCode.ActionNotTakenFileUnavailableOrBusy:
      errorMsg = "下载的文件正在使用,请稍后再试";
      break;
     default:
      errorMsg = "发生未知错误";
      break;
    }
    flag = false;
   }
   catch
   {
    errorMsg = "网络连接发生错误,请稍后再试";
    flag = true;
   }
   finally
   {
    if (ftpResponse != null)
    {
     ftpResponse.Close();
    }
   }
   return flag;
  }