public static boolean connectServer(String host, int port, String user, String password, String defaultPath)
            throws SocketException, IOException {
        ftpClient = new FTPClient();
        // org.apache.commons.net.MalformedServerReplyException: Could not parse response code.
        // Server Reply: SSH-2.0-OpenSSH_7.2
        // ftpClient.addProtocolCommandListener(new PrintCommandListener(new PrintWriter(System.out)));
        // 设置以二进制方式传输
        ftpClient.setDataTimeout(5000);
        ftpClient.setConnectTimeout(connectTimeout);
        ftpClient.setControlEncoding("UTF-8");
        ftpClient.connect(host, port);
        log.info("Connected to " + host + ".");
        log.info("FTP server reply code:" + ftpClient.getReplyCode());
        if (FTPReply.isPositiveCompletion(ftpClient.getReplyCode())) {
            if (ftpClient.login(user, password)) {
                // Path is the sub-path of the FTP path
                if (defaultPath != null && defaultPath.length() != 0) {
                    ftpClient.changeWorkingDirectory(defaultPath);
                }
                return true;
            }
        }
        disconnect();
        return false;
    }

 public static File download(String remote, String local) throws IOException {
        log.info("remote={},local={}", remote, local);
        File downloadFile = null;
        // 检查远程文件是否存在
        FTPFile[] files = ftpClient.listFiles(remote);
        if (files.length == 0) {
            log.info("远程文件不存在: {}, {}", remote, files);
            return downloadFile;
        }

        File f = new File(local);
        OutputStream out = null;
        if (f.exists()) {
            f.delete();
        }
        try {
            //ftpClient.enterLocalPassiveMode();
            out = new FileOutputStream(f);
            boolean upNewStatus = ftpClient.retrieveFile(remote, out);
            out.flush();

            if (upNewStatus) {
                downloadFile = f;
            }
        }
        catch (Exception e) {
            log.error(e.getMessage(), e);
        }
        finally {
            if (out != null) {
                out.close();
            }
        }
        return downloadFile;
    }