如何将安全FTP功能添加到.NET应用程序

using System;
using System.IO;
using System.Net;

public class FTPClient
{
    private string _ftpServerIP;
    private string _ftpUserID;
    private string _ftpPassword;

    public FTPClient(string ftpServerIP, string ftpUserID, string ftpPassword)
    {
        _ftpServerIP = ftpServerIP;
        _ftpUserID = ftpUserID;
        _ftpPassword = ftpPassword;
    }

    public void UploadFile(string remoteFilePath, string localFilePath)
    {
        try
        {
            FileInfo fileInfo = new FileInfo(localFilePath);
            FtpWebRequest request = (FtpWebRequest)WebRequest.Create("ftp://" + _ftpServerIP + "/" + remoteFilePath);
            request.Method = WebRequestMethods.Ftp.UploadFile;
            request.Credentials = new NetworkCredential(_ftpUserID, _ftpPassword);
            request.ContentLength = fileInfo.Length;
            Stream stream = request.GetRequestStream();
            FileStream fileStream = fileInfo.OpenRead();
            byte[] buffer = new byte[fileStream.Length];
            fileStream.Read(buffer, 0, buffer.Length);
            stream.Write(buffer, 0, buffer.Length);
            fileStream.Close();
            stream.Close();
            FtpWebResponse response = (FtpWebResponse)request.GetResponse();
            response.Close();
        }
        catch (Exception ex)
        {
            throw new ApplicationException("Error uploading file.", ex);
        }
    }

    public void DownloadFile(string remoteFilePath, string localFilePath)
    {
        try
        {
            FtpWebRequest request = (FtpWebRequest)WebRequest.Create("ftp://" + _ftpServerIP + "/" + remoteFilePath);
            request.Method = WebRequestMethods.Ftp.DownloadFile;
            request.Credentials = new NetworkCredential(_ftpUserID, _ftpPassword);
            FtpWebResponse response = (FtpWebResponse)request.GetResponse();
            Stream responseStream = response.GetResponseStream();
            FileStream fileStream = new FileStream(localFilePath, FileMode.Create);
            byte[] buffer = new byte[2048];
            int bytesRead = responseStream.Read(buffer, 0, buffer.Length);
            while (bytesRead > 0)
            {
                fileStream.Write(buffer, 0, bytesRead);
                bytesRead = responseStream.Read(buffer, 0, buffer.Length);
            }
            responseStream.Close();
            fileStream.Close();
            response.Close();
        }
        catch (Exception ex)
        {
            throw new ApplicationException("Error downloading file.", ex);
        }
    }

    public string[] ListFiles(string remoteDirectory)
    {
        try
        {
            FtpWebRequest request = (FtpWebRequest)WebRequest.Create("ftp://" + _ftpServerIP + "/" + remoteDirectory);
            request.Method = WebRequestMethods.Ftp.ListDirectory;
            request.Credentials = new NetworkCredential(_ftpUserID, _ftpPassword);
            FtpWebResponse response = (FtpWebResponse)request.GetResponse();
            Stream responseStream = response.GetResponseStream();
            StreamReader reader = new StreamReader(responseStream);
            string[] files = reader.ReadToEnd().Split('\n');
            reader.Close();
            responseStream.Close();
            response.Close();
            return files;
        }
        catch (Exception ex)
        {
            throw new ApplicationException("Error listing files.", ex);
        }
    }

    public void DeleteFile(string remoteFilePath)
    {
        try
        {
            FtpWebRequest request = (FtpWebRequest)WebRequest.Create("ftp://" + _ftpServerIP + "/" + remoteFilePath);
            request.Method = WebRequestMethods.Ftp.DeleteFile;
            request.Credentials = new NetworkCredential(_ftpUserID, _ftpPassword);
            FtpWebResponse response = (FtpWebResponse)request.GetResponse();
            response.Close();
        }
        catch (Exception ex)
        {
            throw new ApplicationException("Error deleting file.", ex);
        }
    }

    public void RenameFile(string remoteFilePath, string newFileName)
    {
        try
        {
            FtpWebRequest request = (FtpWebRequest)WebRequest.Create("ftp://" + _ftpServerIP + "/" + remoteFilePath);
            request.Method = WebRequestMethods.Ftp.Rename;
            request.Credentials = new NetworkCredential(_ftpUserID, _ftpPassword);
            request.RenameTo = newFileName;
            FtpWebResponse response = (FtpWebResponse)request.GetResponse();
            response.Close();
        }
        catch (Exception ex)
        {
            throw new ApplicationException("Error renaming file.", ex);
        }
    }
}