Java socket server shows blank window

Question

I'm writing a program that communcaties two clients through server When I run it without the start method, it works fine and looks like this

but when I try to listen for connections I only get blank white window. The program stops at conn = server.accept() which is quite logical because i dont have a client yet, but why doesn't it how anything?

---

Also, can I get rid of that white border somehow?

import java.awt.*;
import java.awt.print.PrinterException;
import java.io.*;
import java.net.*;

import javax.swing.*;

public class Server extends JFrame {
private ServerSocket server;
private Socket conn;
private JTextArea TA;
private JPanel panel1;
private final int port = 1234;

public Server() {
    super("Server");
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setSize(new Dimension(400, 300));
    Container c = getContentPane();
    c.setBackground(Color.BLACK);
    TA = new JTextArea();
    TA.setEditable(true);
    TA.setBackground(Color.BLACK);
    TA.setForeground(Color.GREEN);
    c.add(new JScrollPane(TA));
    setVisible(true);
    TA.append("Server started.");
}

public void start() {
    try {
        TA.append("ServerSocket created. \n Listering for connections...");
        server = new ServerSocket(port, 2);

        for (int i = 0; i < 2; i++) {
            conn = server.accept();
            TA.append("User " + i + " connected");
        }
    } catch (IOException ioe) {
        System.out.println(ioe);
    }
}
}

import javax.swing.SwingUtilities;

`

 public class ServerLauncher {

public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable(){

        public void run() {
            Server s = new Server();
    //  s.start();
        }

    });

}

}

i was following a youtube guide to write this, and it gets the same bug but looks like it's discontinued after part 3 so I never found out how to fix it. https://www.youtube.com/watch?v=YqTB-S_5mss

Answer 1

It's happening because scheduled in the AWT Event Dispatcher Thread and you're blocking it with the accept method, so nothing shows up.

Try this instead:

public static void main(String[] args) {
    Server s = new Server();
    s.start();
}


public Server() {
    super("Server");
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setSize(new Dimension(400, 300));
    Container c = getContentPane();
    c.setBackground(Color.BLACK);
    TA = new JTextArea();
    TA.setEditable(true);
    TA.setBackground(Color.BLACK);
    TA.setForeground(Color.GREEN);
    c.add(new JScrollPane(TA));
    setVisible(true);
    log(TA, "Server started.");
}

public void log(JTextArea txt, String message) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                txt.append(message);
            }});
}

public void start() {
    try {
        log(TA, "ServerSocket created. \n Listering for connections...");
        server = new ServerSocket(port, 2);

        for (int i = 0; i < 2; i++) {
            conn = server.accept();
            log(TA, "User " + i + " connected");
        }
    } catch (IOException ioe) {
        System.out.println(ioe);
    }
}

Answer 2

• invoking Server s = new Server(); from SwingUtilities.invokeLater(new Runnable(){ in public class ServerLauncher { is wrong idea, you wouldnt to start hard and long running code - Workers Thread from invokeLater(notifier for Event Dispatch Thread), more read in Oracle tutorial Concurency in Swing you would need to start() from SwingWorker, Runnable#Thread, Thread

• TA.append("User " + i + " connected"); you have an issue with (again) with Concurency in Swing, all updates from Worker Thread must be done on EDT, wrapped into invokeLater()

• from Runnable#Thread to start Server s = new Server(); then inside loop to TA.append("User " + i + " connected"); wrapped into invokeLater