FTP client java implementation

Question

I got stuck with FTP client java implementation. All I have to do is to connect to the FTP server and transfer one file to the server.

I managed to make a connection with the ftp server (see code below) and after that I entered passive mode with PASV command. Now I don't know what to do next. I tried to make a new socket after PASV command and to connect it to the FTP server port 20 but that didn't work.

My question is how to initiate file transfer when a connection is made? (My idea is to make a connection with port 20 and to execute STOR command, but I don't know how to do it).

Do you have any ideas or helpful advice?

btw. I have to implement this without using java classes like FTPClient

Here's my code:

   public class FTPtest {

    Socket socket;
    PrintWriter pw;
    BufferedReader input;
    String info = "";

    public FTPtest(){
        try{
            socket = new Socket("some_ftp_server", 21);
            logUsername();
            closeEverything();
        }
        catch(IOException ioe){
            System.out.println("error");
        }
    }

    public void logUsername()throws IOException{
        input = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        pw = new PrintWriter(socket.getOutputStream());

        //user
        pw.write("USER some_user\n");
        pw.flush();
        System.out.println(input.readLine());

        //pass
        pw.write("PASS some_pass");
        pw.flush();
        System.out.println(input.readLine());
        System.out.println(input.readLine());

        //PASV
        pw.write("PASV");
        pw.flush();
    }

    public void closeEverything() throws IOException{
        input.close();
        pw.close();
        socket.close();
    }
    public static void main(String[]args){
        new FTPtest();
    }
}

Do you want to do a FTP Client yourself? Because if you are just searching for a way to connect to an ftp server and do some operations you can take a look at Apache Commons-Net which has an integrated FTP Client class — BackSlash
I want to do FTP Client myself without using any FTP client classes. — Branko

Nickolay Olshevsky Nickolay Olshevsky · Accepted Answer · 2013-04-10T15:42:48

You'd better use already existent FTP client library. As for PASV request - server in answer to it returnes encoded IP address and port to which you should connect for data connection.

FTP client java implementation

3 Answers