public bool DownloadFile(string localFilePath, string ftpFilePath)
        {
            bool success = false;
            FtpWebRequest ftpWebRequest = null;
            FtpWebResponse ftpWebResponse = null;
            Stream ftpResponseStream = null;
            FileStream outputStream = null;
            
            try
            {
                string dir = Path.GetDirectoryName(localFilePath);
                if (!Directory.Exists(dir))
                {
                    Directory.CreateDirectory(dir);
                }
                if (File.Exists(localFilePath))
                {
                    File.Delete(localFilePath);
                }
                
                ftpWebRequest = (FtpWebRequest)FtpWebRequest.Create(new Uri(ftpFilePath));
                ftpWebRequest.Credentials = new NetworkCredential(ftpUser, ftpPassword);//匿名的话，这里赋值为空
                ftpWebRequest.UseBinary = true;
                ftpWebRequest.Method = WebRequestMethods.Ftp.DownloadFile;

                ftpWebResponse = (FtpWebResponse)ftpWebRequest.GetResponse();

                ftpResponseStream = ftpWebResponse.GetResponseStream();
                long contentLength = ftpWebResponse.ContentLength;

                int bufferSize = 2048;
                byte[] buffer = new byte[bufferSize];
                int readCount;

                readCount = ftpResponseStream.Read(buffer, 0, bufferSize); 
                outputStream = new FileStream(localFilePath, FileMode.Create);

                while (readCount > 0)
                {
                    outputStream.Write(buffer, 0, readCount);
                    readCount = ftpResponseStream.Read(buffer, 0, bufferSize);
                }
                
                success = true;
            }
            catch (Exception e)
            {
                success = false;
                throw;
            }
            finally
            {
                if (outputStream != null)
                {
                    outputStream.Close();
                }

                if (ftpResponseStream != null)
                {
                    ftpResponseStream.Close();
                }

                if (ftpWebResponse != null)
                {
                    ftpWebResponse.Close();
                }
            }

            return success;
        }