FTP判断目录是否存在的方法没有直接方法，只能使用间接的方法。

使用WebRequestMethods.Ftp.ListDirectory来判断，但这个方法存在一定的问题，就是如果这个目录存在，但此目录下既没有目录，也没有文件，则这个方法就有问题。

 private static bool DirectoryExist(FtpInfo info, string dirName, bool KeepAlive)
        {
            //修复iis设置为framework4.0的时候，ftp目录不存在时返回还是true的问题。
            try
            {
                FtpWebRequest reqFTP = GetFtpWebRequest(info, dirName, KeepAlive);
                reqFTP.Method = WebRequestMethods.Ftp.ListDirectory;
                FtpWebResponse response = (FtpWebResponse)reqFTP.GetResponse();

                StreamReader reader = new StreamReader(response.GetResponseStream(), Encoding.UTF8);
                string line = reader.ReadLine();
                if (line == null)
                {
                    LogInfo.Error("目录不存在 FTP ListDirectory：dirName=" + dirName + ",line=" + line);
                    return false;
                }
                else
                {
                    LogInfo.Info("FTP ListDirectory：dirName=" + dirName + ",line=" + line);
                }
                reader.Close();
                response.Close();
                return true;
            }
            catch (Exception ex)
            {
                LogInfo.Error("目录异常 FTP ListDirectoryDetails：url=" + dirName, ex);
                return false;
            }
        }
        private static FtpWebRequest GetFtpWebRequest(FtpInfo info, string url, bool KeepAlive)
        {
            string username = info.userName;
            string password = info.passWord;
            try
            {
                FtpWebRequest request = (FtpWebRequest)FtpWebRequest.Create(new Uri(url));
                request.UseBinary = true;
                request.KeepAlive = KeepAlive;
                request.Credentials = new NetworkCredential(username, password);

                request.UsePassive = !info.transferType;//配置的定义和属性的定义刚好相反
                //如果客户端应用程序的数据传输过程侦听数据端口上的连接，则为 false；如果客户端应在数据端口上启动连接，则为 true。 默认值是 true
                LogInfo.Debug("FTP上传文件：UsePassive=" + request.UsePassive);
                if (info.ftps)
                {
                    request.Proxy = null;
                    request.EnableSsl = true;//FTPS需要配置
                    ServicePointManager.ServerCertificateValidationCallback =
                  new RemoteCertificateValidationCallback(ValidateServerCertificate);
                }
                return request;
            }
            catch (Exception e)
            {
                LogInfo.Error("FTP异常：url=" + url + "," + info, e);
                throw e;
            }
        }
        /// <summary>
        /// 把响应流转换为文本。
        /// </summary>
        /// <param name="rsp">响应流对象</param>
        /// <param name="encoding">编码方式</param>
        /// <returns>响应文本</returns>
        private static string GetResponseAsString(FtpWebResponse rsp)
        {
            System.IO.Stream stream = null;
            StreamReader reader = null;
            try
            {
                // 以字符流的方式读取HTTP响应
                stream = rsp.GetResponseStream();
                reader = new StreamReader(stream);
                return reader.ReadToEnd();
            }
            finally
            {
                // 释放资源
                if (reader != null) reader.Close();
                if (stream != null) stream.Close();
                if (rsp != null) rsp.Close();
            }
        }      

 但这个方法可以改进，判断父目录下是否存在指定的目录就可以改进

 /// <summary>
        /// 判断父目录下是否存在当前目录，如果存在当前目录，在返回true
        /// </summary>
        /// <param name="info"></param>
        /// <param name="ParentdirName"></param>
        /// <param name="KeepAlive"></param>
        /// <param name="currentFolderName"></param>
        /// <returns></returns>
        private static bool DirectoryExist(FtpInfo info, string ParentdirName, bool KeepAlive, string currentFolderName)
        {
            //修复iis设置为framework4.0的时候，ftp目录不存在时返回还是true的问题。
            try
            {
                FtpWebRequest reqFTP = GetFtpWebRequest(info, ParentdirName, KeepAlive);
                reqFTP.Method = WebRequestMethods.Ftp.ListDirectory;
                FtpWebResponse response = (FtpWebResponse)reqFTP.GetResponse();

                StreamReader reader = new StreamReader(response.GetResponseStream(), Encoding.UTF8);
                string line = reader.ReadToEnd();
                if (line == null)
                {
                    LogInfo.Error("目录不存在 FTP ListDirectory：ParentdirName=" + ParentdirName + ",currentFolderName = " + currentFolderName+", line=" + line);
                    return false;
                }
                else
                {
                    LogInfo.Info("FTP ListDirectory ParentdirName=" + ParentdirName + ",currentFolderName = " + currentFolderName + ", line=" + line);
                    if (line.IndexOf(currentFolderName) >=0)
                    {
                        return true;
                    }
                    LogInfo.Error("目录不存在 FTP ParentdirName=" + ParentdirName + ",currentFolderName = " + currentFolderName + ", line=" + line);
                }
                reader.Close();
                response.Close();
                return false;
            }
            catch (Exception ex)
            {
                LogInfo.Error("目录异常 FTP ListDirectoryDetails：url=" + ParentdirName, ex);
                return false;
            }
        }