Question

I am trying to “Write two Java programs implementing the FTP server with responses to USER and PASS, with thread-per-client and thread pool, respectively.” I am just trying to make sure I have everything in order before turning it in. Here is my source code. The only trouble I am having is figuring out what to do with “FTPProtocol client;” Should I just destroy it after I have the thread.start?

FTPServer.java

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;


 public class FTPserver
{   
public static void main(String [] args)
{
    if (args.length != 1) 
        throw new IllegalArgumentException( "Parameter(s): <Port>");

    int threadPoolSize = 10;
    int port = Integer.parseInt(args[0]); 

    final ServerSocket server;
    try 
    {
        server = new ServerSocket(port);
    } 
    catch (IOException e1) 
    {
        return;
    }

    for (int i = 0; i < threadPoolSize; i++) 
    {
        Thread thread = new Thread() 
        {
            public void run() 
            {
                while (true) 
                {
                    try 
                    {
                        Socket sock = server.accept();
                        FTPProtocol client = new FTPProtocol(sock);
                    } 
                    catch (IOException e)
                    {
                        System.err.println(e.getMessage());
                        return;
                    }
                }
            }
        };
        thread.start();
    }
}
}

FTPProtocol.java

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.Socket;

class FTPProtocol implements Runnable
{
static String greeting = "220 Service Ready.\r\n";
static String needPassword = "331 User name ok, need password.\r\n";
static String closing = "421 Service not available, closing control connection.\r\n";
static byte[] reply220 = null;
static byte[] reply331 = null;
static byte[] reply421 = null;

    Socket sock = null;
    public FTPProtocol(Socket so)
    {
        sock = so; 
        reply220 = greeting.getBytes();
        reply331 = needPassword.getBytes();
        reply421 = closing.getBytes();
    }

    public void run()
    { 
        handleFTPClient(sock); 
    }

    void handleFTPClient(Socket sock)
    {
        InputStream is = null;
        OutputStream os = null;
        byte[] inBuffer = new byte[1024];

        try 
        {
            is = sock.getInputStream();
            os = sock.getOutputStream();
            os.write(reply220);
            int len = is.read(inBuffer);
            System.out.write(inBuffer, 0, len);
            os.write(reply331);
            len = is.read(inBuffer);
            System.out.write(inBuffer, 0, len);
            os.write(reply421);
            sock.close();
        } 
        catch (IOException e)
        {
            System.err.println(e.getMessage());
            return;
        }
    }
}

Answer 1

Am I missing something here? You are creating an on object whose type implements Runnable (for no apparent reason):

FTPProtocol client = new FTPProtocol(sock);

and then you are not doing anything with it.

Did you mean to start a thread with that Runnable? Or pass it to a thread pool:

ExecutorService exec = Executors.newFixedThreadPool(threadPoolSize);

while (true) {
   try {
      Socket sock = server.accept();
      exec.submit(new FTPProtocol(sock));
   } catch (IOException e) {
      System.err.println(e.getMessage());
      return;
   }
}

This will ensure that you are not starting more threads than threadPoolSize and that the appropriate run method of FTPProtocol is called for each object.