public class VistaPrincipal extends JFrame {

	private JPanel contentPane;
	private Runnable server = null;

	/**
	 * Launch the application.
	 */
	public static void main(String[] args) {
		EventQueue.invokeLater(new Runnable() {
			public void run() {
				try {
					VistaPrincipal frame = new VistaPrincipal();
					frame.setVisible(true);					
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		});
	}

	/**
	 * Create the frame.
	 */
	public VistaPrincipal() {
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setBounds(100, 100, 497, 310);
		contentPane = new JPanel();
		contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
		setContentPane(contentPane);
		contentPane.setLayout(null);
		
		JLabel lblClientes = new JLabel("Clientes: ");
		lblClientes.setBounds(10, 11, 77, 14);
		contentPane.add(lblClientes);
		
		JList<String> listaCLientes = new JList<String>();
		JList<String> listaLog = new JList<String>();
		
		
		JPanel panelClientes = new JPanel();
		panelClientes.setBounds(10, 29, 110, 202);
		contentPane.add(panelClientes);
		panelClientes.setLayout(null);
		
		JScrollPane scrollClientes = new JScrollPane(listaCLientes);
		scrollClientes.setBounds(0, 0, 110, 202);
		panelClientes.add(scrollClientes);
		
		JPanel panelLog = new JPanel();
		panelLog.setBounds(130, 29, 341, 202);
		contentPane.add(panelLog);
		panelLog.setLayout(null);
		
		JScrollPane scrollLog = new JScrollPane(listaLog);
		scrollLog.setBounds(0, 0, 341, 232);
		panelLog.add(scrollLog);
		
		JButton btnSalir = new JButton("Salir");
		btnSalir.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent arg0) {
				dispose();
			}
		});
		btnSalir.setBounds(382, 242, 89, 23);
		contentPane.add(btnSalir);
		
		JButton btnIniciar = new JButton("Iniciar");
		btnIniciar.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent arg0) {
				
				try {
					 server = new Servidor();
				} catch (IOException e) {
					JOptionPane.showMessageDialog(null, "Error al crear el servidor, cierre la maquina virtual de java e intentelo nuevamente", "Error!", JOptionPane.ERROR_MESSAGE);
				}
				
				if (server !=  null) {
					Thread hilo = new Thread(server);
					hilo.run();
				}
			}
		});
		btnIniciar.setBounds(20, 242, 89, 23);
		contentPane.add(btnIniciar);
		
		JButton btnStop = new JButton("Stop");
		btnStop.setBounds(119, 242, 89, 23);
		contentPane.add(btnStop);
		
		//FIN CREACION DE VISTA
	}
}

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

import javax.swing.JOptionPane;

public class Servidor implements Runnable {
	
	private int puerto = 20000;
	private ServerSocket socket;
	
	public Servidor() throws IOException {
		this.socket = new ServerSocket(this.puerto);
	}
	
	public void run() {
		
		while (true) {
			Socket cliente = null;
			try {
				cliente = socket.accept();
			} catch (IOException e) {
				JOptionPane.showMessageDialog(null, "Error al aceptar nuevo Cliente", "Error!", JOptionPane.ERROR_MESSAGE);
			}
			
			if (cliente != null) {
				Runnable nuevoCliente = new HiloCliente(cliente);
				Thread hilo = new Thread(nuevoCliente);
				hilo.run();
			}
		}
	}

}

import java.net.Socket;

public class HiloCliente implements Runnable {
	
	private Socket socket;
	
	public HiloCliente (Socket socket) {
		
		this.socket = socket;
	}

	@Override
	public void run() {
		// TODO Auto-generated method stub
		System.out.println("Cliente");
	}

}