Mutlithreading with GUI problem

Question

hey guys,
I was working on some Socket programming assignment and encountered an intersting problem.
i am using Swing for GUI and Threads to communicate with clients.
My server GUi has a JButton("Start Server") to trigger the Server. or we can say.. it starts accepting connection( SocketObj = ServerSocketObj.accept() )
problem:
as soon as i press the only Button(i.e. StartServer Button) on my Server GUI. whole GUI freezes!
but Server is working... all updates on GUI are missing.. cant repaint components, etc. neither WindowClosing event , setDefaultCloseOperation()) is working.
i did some research.. found that swing components are not thread safe,
also found some close answers,, along the lines of.. Event Dispatch Thread, SwingUtilities.invokeLater(Runnable), SwingWorker class , but neither work or maybe i did not implement them properly..
Attachment contains my code for:
Server.java : Server class conatins main()
ServerGUI.java : gui for server.. called from Server Class
ClientHandler.java : Thread for handling clients.. also called from Serve class
Cleint.java : simple client to connect to server at localhost
Any sort of help would be highly obliged.
thanks in advance.
- Ravi

Answer 1

here is the code...
Server.java
import java.net.*;
import java.io.*;
public class Server {
    private ServerSocket ss;
    private Socket sc;
    public ServerSocket getSs() {
        return ss;
    public void setSs(ServerSocket ss) {
        this.ss = ss;
    public Socket getSc() {
        return sc;
    public void setSc(Socket sc) {
        this.sc = sc;
    public Server() {
        try{
        ss = new ServerSocket(4000);
        }catch(IOException e){e.printStackTrace();}
        startGUI();
    public void startGUI()
        new ServerGUI(this);
    public void getConnection()
        int i = 1;
        try {
            Socket sc = getSc();
            while (true) {
                sc = getSs().accept();
                Thread t = new Thread(new ClientHandler(sc,i));
                t.start();
                System.out.println("got client " + i);
                i++;
        } catch (IOException e) {
            e.printStackTrace();
    public static void main(String[] args) {
        new Server();
}ServerGUI.java
import java.net.*;
import java.io.*;
public class ServerGUI extends javax.swing.JFrame {
     private javax.swing.JButton jButton1;
    Server m;
    public ServerGUI(Server m) {
        initComponents();
        this.m=m;
        setVisible(true);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
    private void initComponents() {
        jButton1 = new javax.swing.JButton();
        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        jButton1.setText("jButton1");
        jButton1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton1ActionPerformed(evt);
        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                .addContainerGap(178, Short.MAX_VALUE)
                .addComponent(jButton1)
                .addGap(147, 147, 147))
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(93, 93, 93)
                .addComponent(jButton1)
                .addContainerGap(184, Short.MAX_VALUE))
        pack();
    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
        m.getConnection();
}ClientHandler.java
import java.net.*;
public class ClientHandler implements Runnable {
    Socket sock;
    int n;
    public ClientHandler(Socket s, int n) {
        sock = s;
        this.n = n;
    public void run() {
        while (true) {
            System.out.println("Client Thread: " + n);
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
}Client.java
import java.net.*;
import java.io.*;
public class Client {
    Socket sc;
    public Client() {
        try{
        sc=new Socket("127.0.0.1",4000);
        System.out.println("got server");
        }catch(UnknownHostException e){e.printStackTrace();}
        catch(IOException e){e.printStackTrace();}
    public static void main(String args[])
        new Client();
}