打开多个FTP连接

Question

I'm opening multiple FTP connections in my code in different threads. There can be two connections to the same FTP server using the same credentials.

Can this cause a problem with the active/passive backchannel transfering the data? The actual problem I'm having is that a certain login fails even though it worked seconds before in a different thread. It is hard to reproduce.

Another question, is active or passive the standard setting? Which one is better?

FTPClient ftp = new FTPClient();

ftp.setDefaultTimeout(timeoutMilliseconds);
ftp.setDataTimeout(timeoutMilliseconds);
ftp.setConnectTimeout(timeoutMilliseconds);
//ftp.setSoTimeout(1000);
//ftp.setControlKeepAliveTimeout(1000);
//ftp.setControlKeepAliveReplyTimeout(1000);

ftp.connect(serverAddress, serverPort);
logger.info("Connected successfully to " + serverAddress + ":" + serverPort);
boolean login = ftp.login(username, password);
logger.info("Logged in successfully to " + serverAddress + ":" + serverPort);


ftp.disconnect();

Answer 1

Passive mode is recommended. Please find the below settings that I have used in my project. You can refer to the https://www.jscape.com/blog/bid/80512/active-vs-passive-ftp-simplified for further details.

FTPClient ftp = new FTPClient();
        ftp.addProtocolCommandListener(new PrintCommandListener(new PrintWriter(System.out)));
        ftp.connect(host, port);
        int reply = ftp.getReplyCode();
        if (!FTPReply.isPositiveCompletion(reply)) {
            ftp.disconnect();
            throw new IllegalArgumentException("Not able to connect to the ftp Server ");
        }
        ftp.login(userName, password);
        ftp.setFileType(FTP.BINARY_FILE_TYPE);
        ftp.enterLocalPassiveMode();
        ftp.setBufferSize(100000);
        ftp.setConnectTimeout(1200000);
        ftp.setDataTimeout(1200000);
        ftp.setDefaultTimeout(1200000);