Re: Server and multiple sockets

From:
SadRed <cardinal_ring@yahoo.co.jp>
Newsgroups:
comp.lang.java.programmer
Date:
23 Apr 2007 16:09:32 -0700
Message-ID:
<1177369772.381506.87560@y5g2000hsa.googlegroups.com>
On Apr 24, 7:15 am, Chris <cc_brews...@yahoo.com> wrote:

On Apr 22, 5:59 pm, Chris <cc_brews...@yahoo.com> wrote:

I'm a student, trying to write a server that can handle multiple
clients. It's closer to working than I was expecting but if I use
client 1, then client 2, client 1 then freezes. And then I can't close
the windows and have to stop the OS processes. The problem occurs with
this statement after port is defined:

      ServerSocket ss = new ServerSocket(port);

which causes this message:

     java.net.BindException: Address already in use: JVM_Bind

At that point no clients are running and nothing else has happened
with ports. I actually don't understand why the clients work at all,
since the socket doesn't seem to have been created successfully. After
the message above (and a trace), no other system messages appear
unless I try to close a window.

The following code includes comments using caps and ***, showing where
the trouble occurs. Any help greatly appreciated.

Chris
________________________________

package com.abc.server;

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.net.*;
import java.io.*;

public class Server extends JPanel implements Runnable {
    private static JTextArea serverLog;
    private static int port;
    private static Socket soc;
    private static ObjectOutputStream oos;
    private static ObjectInputStream ois;
    private Thread internalThread;
    private static PrintStream out;

    public static void main(String[] args) {
        JFrame f = new JFrame("Server");
        f.setSize(600, 350);
        f.setDefaultCloseOperation(f.EXIT_ON_CLOSE);
        f.setVisible(true);
        serverLog = new JTextArea();
        f.add(serverLog);

        out = new PrintStream(new TextAreaOutputStream(serverLog));
        System.setOut(out);
        System.setErr(out);

        f.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                try {
                    ois.close();
                    oos.flush();
                    oos.close();
                    soc.close();
                } catch ( IOException ioe ) {
                    System.out.println(ioe + "\n");
                    ioe.printStackTrace();
                }
                System.exit(0);
            }
        });
        port = 2001;
        Server server = new Server();
        System.out.println("Leaving main.");
    }

    public Server() {
        internalThread = new Thread(this);
        internalThread.start();
    }

    public void run() {
        System.out.println("Server ready.");

            int i = 1;
            System.out.println("Start of ");
            try {
            System.out.println("Start of connecting section. i = " +
i);
// *** EXECUTES CORRECTLY TO HERE
                ServerSocket ss = new ServerSocket(port);
// *** MESSAGE ISSUED HERE BUT SOCKET PARTIALLY WORKS
                for ( ;; ) {
                    Socket sock = ss.accept();
                    System.out.println("Got connection #" + i);
                    ClientService cs = new ClientService(sock, i,
out);
                    i++ ;
                }
            } catch ( IOException ioe ) {
                System.out.println(ioe + "\n");
                ioe.printStackTrace();
            }
// *** FOLLOWING PRINTS CORRECTLY BUT NO OTHER MESSAGES
        System.out.println("Connection established.");
    }

}

class ClientService implements Runnable {
    private static ObjectOutputStream oos;
    private static ObjectInputStream ois;
    private Thread internalThread;
    private Socket soc;
    private int counter;

    public ClientService(Socket s, int ctr, PrintStream outTxtArea) {
        soc = s;
        counter = ctr;
        PrintStream out = outTxtArea;
        System.setOut(out);
        System.setErr(out);
        internalThread = new Thread(this);
        internalThread.start();
        internalThread.interrupt();
    }

    public void run() {
        System.out.println("Thread for client #" + counter);
        try {
            final InputStream is = soc.getInputStream();
            oos = new ObjectOutputStream(soc.getOutputStream());
            ois = new ObjectInputStream(is);
            boolean done = false;
            while ( !done ) {
                String strFrmClnt = (String) ois.readObject();
                String strToClnt = strFrmClnt.length() + " - " +
strFrmClnt;
                if ( strFrmClnt == null ) {
                    done = true;
                } else {
                    oos.writeObject(strToClnt);
                }
            }
            ois.close();
            oos.flush();
            oos.close();
            soc.close();
        } catch ( ClassNotFoundException cnfe ) {
            System.out.println(cnfe + "\n");
            cnfe.printStackTrace();
        } catch ( IOException ioe ) {
            System.out.println(ioe + "\n");
            ioe.printStackTrace();
        }
    }

}- Hide quoted text -

- Show quoted text -


I received a number of responses with interesting suggestions but
someone in my company found the problem-- embarrassingly simple as
these things sometimes are. My input and output streams in the
ClientService class were declared static. So the conflict between the
client instances had to happen. (I guess I was sticking "static" on
things because Eclipse kept bugging me about variables.) Thanks to all
who looked over my code.


Awfull. Your Server class also has a few static fields. We had
taken for granted that there can't be such code in c/s program.
But there were!

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