Server, thread and limited connexions

Question

I use this code for my server. I got it from the book "Java thread" written by Scott Oaks and Henry Wong" and edited by O'Reilly.
This code works very good. I just want to implement a limited allowed connexions at a same time (ie 20 or 30 connexions possible at a same time).
I think a simple count of the created threads isn't enougth because i can't figure out how to decrease it. I was thinking using thread pool and counting the threads inside, so that i know exactly how many connexions are opened.
Any advice about this is welcome.
Here is the code :
import java.net.*;
import java.io.*;
public class TCPServer implements Cloneable, Runnable
    Thread runner = null;
    ServerSocket server = null;
    Socket data = null;
    boolean ShouldStop = false;
    public synchronized void startServer(int port) throws IOException
        if(runner == null)
            server = new ServerSocket(port);
            runner = new Thread(this);
            runner.start();
    public synchronized void stopServer()
        if(server != null)
            ShouldStop = true;
            runner.interrupt();
            runner = null;
            try
                server.close();
            catch(IOException ioe)
                //ioe.printStackTrace();
            server = null;
    public void run()
        if(server != null)
            while(!ShouldStop)
                try
                    Socket datasocket = server.accept();
                    TCPServer newSocket = (TCPServer) clone();
                    newSocket.server = null;
                    newSocket.data = datasocket;
                    newSocket.runner = new Thread(newSocket);
                    newSocket.runner.start();
                catch(Exception e)
        else
            run(data);
    public void run(Socket data)
}This class is used to implement the server. A derivated class is used to treat the connexion. I wish to implement the counter in this class if possible.
In advance thanks.

Answer 1

To define the maximum allowed connections, use this constructor for ServerSocket
public ServerSocket(int port, int backlog)Backlog being the maximum allowed connections at a time. Any aditional connection attempts will be rejected.
public class TCPServer implements Cloneable, Runnable{
    Thread runner = null;
    ServerSocket server = null;
    Socket data = null;
    boolean ShouldStop = false;
    private final int MAXIMUM_CONNECTIONS = 20; //or 30 or whatever you want your maximum to be
        public synchronized void startServer(int port) throws IOException {
        if(runner == null) {
            server = new ServerSocket(port, MAXIMUM_CONNECTIONS);
            runner = new Thread(this);
            runner.start();
    public synchronized void stopServer()    {
        //.......etc
}