FTPClient - how to use active mode

ftp, java, mode

Solution

This is old, but I stumbled onto it trying to solve the issue myself.

You have to call `enterLocalPassiveMode()` after calling `connect()` and before calling `login()`.

See my example below which initialises the `FTPClient` in local passive mode, lists files for a given directory, then closes the connections.

private static FTPClient client;

public static void main(String [] args) {
    
    //initialise the client
    initPassiveClient();
    
    //do stuff
    FTPFile [] files = listFiles("./");
    if( files != null ) {
        logger.info("Listing Files:");
        for( FTPFile f : files) {
            logger.info(f.getName());
        }
    }
    
    //close the client
    close();
}

/**
 * getPassiveClient retrive a FTPClient object that's set to local passive mode
 *
 * @return FTPClient
 */
public static FTPClient initPassiveClient() {
    if( client == null ) {
        logger.info("Getting passive FTP client");
        client = new FTPClient();

        try {

            client.connect(server);
            // After connection attempt, you should check the reply code to verify
            // success.
            int reply = client.getReplyCode();

            if(!FTPReply.isPositiveCompletion(reply)) {
                client.disconnect();
                logger.error("FTP server refused connection.");
                System.exit(0);
            }

            //after connecting to the server set the local passive mode
            client.enterLocalPassiveMode();

            //send username and password to login to the server
            if( !client.login(user, pass) ) {
                logger.error("Could not login to FTP Server");
                System.exit(0);
            }
        } catch (SocketException e) {
            String message = "Could not form socket";
            logger.error(message+"\n", e);
            System.exit(0);
        } catch (IOException e) {
            String message = "Could not connect";
            logger.error(message+"\n", e);
            System.exit(0);
        }
    }
    
    return client;
}

public static void close() {
    if( client == null ) {
        logger.error("Nothing to close, the FTPClient wasn't initialized");
        return;
    }
    
    //be polite and logout & close the connection before the application finishes
    try {
        client.logout();
        client.disconnect();
    } catch (IOException e) {
        String message = "Could not logout";
        logger.error(message+"\n", e);
    }
}

/**
 * listFiles uses the FTPClient to retrieve files in the specified directory
 *
 * @return array of FTPFile objects
 */
private static FTPFile[] listFiles(String dir) {
    if( client == null ) {
        logger.error("First initialize the FTPClient by calling 'initFTPPassiveClient()'");
        return null;
    }
    
    try {
        logger.debug("Getting file listing for current director");
        FTPFile[] files = client.listFiles(dir);

        return files;
    } catch (IOException e) {
        String message = "";
        logger.error(message+"\n", e);
    }
    
    return null;
}

Problem

I made a small application that should upload files to an FTP server. The thing is that I used passive mode with the method ``` enterLocalPassiveMode() ``` Recently I was told that no passive mode is allowed on the FTP server, so I should make my application work in active mode. I suppose it couldn't be done by simply changing the method to ``` enterLocalActiveMode() ``` What else should I change in the application to ensure it's working in active mode. Here's a code snippet which makes the connection to the server: ``` public void connect() throws FTPException { try { ftpClient.connect(server, port); replyCode = ftpClient.getReplyCode(); if (!FTPReply.isPositiveCompletion(replyCode)) { printText("FTP server refused connection."); throw new FTPException("FTP server refused connection."); } boolean logged = ftpClient.login(user, pass); if (!logged) { ftpClient.disconnect(); printText("Could not login to the server."); throw new FTPException("Could not login to the server."); } ftpClient.enterLocalPassiveMode(); } catch (IOException ex) { printText("I/O errortest: " + ex.getMessage()); throw new FTPException("I/O error: " + ex.getMessage()); } } ``` Some guidance to what I have to change?

Original source