java使用FTPS TLS连接到FTP

Question

尝试使用FTP连接到FTP服务器（“TLS”，隐式）时出错

FTPSClient ftps = new FTPSClient("TLS");
ftps.addProtocolCommandListener(new PrintCommandListener(new PrintWriter(System.out)));
int reply;
    try {
        ftps.connect("server");
    } catch (IOException ex) {
        Logger.getLogger(Ftpimport.class.getName()).log(Level.SEVERE, null, ex);
    }
reply = ftps.getReplyCode();
if (!FTPReply.isPositiveCompletion(reply)) {
    try {
        ftps.disconnect();
    } catch (IOException ex) {
        Logger.getLogger(Ftpimport.class.getName()).log(Level.SEVERE, null, ex);
    }
    throw new Exception("Exception in connecting to FTPs Server");
}
ftps.execPBSZ(0); 
ftps.execPROT("P");
ftps.login("user", "pass");
ftps.setFileType(FTP.BINARY_FILE_TYPE);
ftps.enterLocalPassiveMode();

它在“234 AUTH命令正常。期待TLS协商”中出现使用SSLContext和TrustManager进行了尝试，但都是一样的