Accessing FTP Server using Java

[Chetan Parekh]

Hello!,

I downloaded following class from the net that allows to login in FTP Server.

It was working fine, but when I added ls command (I have added comment see that) , it give error saying [i]500 'LS': command not understood.[i]

How to solve this problem?

Reg,
Chetan

import java.io.BufferedReader;
import java.io.PrintWriter;
import java.io.InputStreamReader;
import java.net.Socket;
 
public class FTPLogin {
 
    public static void main (String args[]) {
        Socket socket = null;
        BufferedReader in = null;
        PrintWriter out = null;
        String line = null;
 
        if (args.length != 3) {
            System.out.println ("USAGE: IP USER PASS");
        } else  {
try {
                socket = new Socket (args[0], 21);
                in = new BufferedReader (new InputStreamReader(socket.getInputStream()));
                out = new PrintWriter (socket.getOutputStream());
                out.println("user "+ args[1]);
                out.println("pass "+ args[2]);
                out.println("pwd");
               
                //Following command is not working
                out.println("ls");
                                
                out.println ("quit");
                out.flush();
 
                while ( (line = in.readLine()) != null) {
                    System.out.println(line);
                }
 
            } catch (Exception e) {
                System.out.println(e.getMessage());
            } finally {
                try {
                    out.close();
                    in.close();
                    socket.close();
                } catch (Exception fe) {
                    System.out.println ("RESOURCE CLOSE EXCEPTION " + fe.getMessage());
                }
            }
        }
    }
}

[Joe Ess]

FTP is a pretty loose protocol. Some servers implement features that others do not. Depending on your server, "LS" may not be supported:

5. DECLARATIVE SPECIFICATIONS

5.1. MINIMUM IMPLEMENTATION

In order to make FTP workable without needless error messages, the
following minimum implementation is required for all servers:

TYPE - ASCII Non-print
MODE - Stream
STRUCTURE - File, Record
COMMANDS - USER, QUIT, PORT,
TYPE, MODE, STRU,
for the default values
RETR, STOR,
NOOP.

The default values for transfer parameters are:

TYPE - ASCII Non-print
MODE - Stream
STRU - File

All hosts must accept the above as the standard defaults.

RFC 959 - File Transfer Protocol
As a matter of fact, I don't see "LS" at all in the RFC.
Try using a command-line FTP client to log in. Typing in "help" may get you a list of valid commands for that server.

[Arnold Reuser]

Maybe you could take also look at Commons Net for the base classes of FTP.
Around these bases classes Julian Robichaux has already written a wrapper that make the usage of FTP within java a bit less hard. You can find his code over here : http://www.nsftools.com/tips/JakartaFtpWrapper.java

[Chetan Parekh]

Thanks a lot!!

I will implement this thing.

Warm Regards,
Chetan