/** 
 * This program is an example from the book "Internet 
 * programming with Java" by Svetlin Nakov. It is freeware. 
 * For more information: http://www.nakov.com/books/inetjava/ 
 */ 
import java.io.*; 
import java.net.*; 
import java.util.Vector; 
 
public class ChatServer { 
    public static void main(String[] args) 
    throws IOException { 
        ServerSocket serverSocket = new ServerSocket(5555); 
        System.out.println("Chat server started on port " + 
            serverSocket.getLocalPort()); 
 
        ServerMsgDispatcher dispatcher = 
            new ServerMsgDispatcher(); 
        dispatcher.start(); 
 
        while (true) { 
            Socket clientSocket = serverSocket.accept(); 
            ClientListener clientListener = 
                new ClientListener(clientSocket, dispatcher); 
            dispatcher.addClient(clientSocket); 
            clientListener.start(); 
        } 
    } 
} 
 
class ClientListener extends Thread { 
    private Socket mSocket; 
    private ServerMsgDispatcher mDispatcher; 
    private BufferedReader mSocketReader; 
 
    public ClientListener(Socket aSocket, 
        ServerMsgDispatcher aServerMsgDispatcher) 
    throws IOException { 
        mSocket = aSocket; 
        mSocketReader = new BufferedReader( 
            new InputStreamReader( 
                mSocket.getInputStream())); 
        mDispatcher = aServerMsgDispatcher; 
    } 
 
    public void run() { 
        try { 
            while (!isInterrupted()) { 
                String msg = mSocketReader.readLine(); 
                if (msg == null) 
                    break; 
                mDispatcher.dispatchMsg(mSocket, msg); 
            } 
        } catch (IOException ioex) { 
            System.err.println("Error communicating " + 
                "with some of the clients."); 
        } 
        mDispatcher.deleteClient(mSocket); 
    } 
} 
 
class ServerMsgDispatcher extends Thread { 
    private Vector mClients = new Vector(); 
    private Vector mMsgQueue = new Vector(); 
 
    public synchronized void addClient(Socket aClientSocket) { 
        mClients.add(aClientSocket); 
    } 
 
    public synchronized void deleteClient(Socket aClientSock) { 
        int i = mClients.indexOf(aClientSock); 
        if (i != -1) { 
            mClients.removeElementAt(i); 
            try { 
                aClientSock.close(); 
            } catch (IOException ioe) { 
                // Probably the socket already is closed 
            } 
        } 
    } 
 
    public synchronized void dispatchMsg( 
            Socket aSocket, String aMsg) { 
        String IP = aSocket.getInetAddress().getHostAddress(); 
        String port = "" + aSocket.getPort(); 
        aMsg = IP + ":" + port + " : " + aMsg + "\n\r"; 
        mMsgQueue.add(aMsg); 
        notify(); 
    } 
 
    private synchronized String getNextMsgFromQueue() 
    throws InterruptedException { 
        while (mMsgQueue.size() == 0) 
            wait(); 
        String msg = (String) mMsgQueue.get(0); 
        mMsgQueue.removeElementAt(0); 
        return msg; 
    } 
 
    private synchronized void sendMsgToAllClients(String aMsg) {  
        for (int i=0; i<mClients.size(); i++) { 
            Socket socket = (Socket) mClients.get(i); 
            try { 
                OutputStream out = socket.getOutputStream();  
                out.write(aMsg.getBytes()); 
                out.flush(); 
            } catch (IOException ioe) { 
                deleteClient(socket); 
            } 
        } 
    } 
 
    public void run() { 
        try { 
            while (true) { 
                String msg = getNextMsgFromQueue(); 
                sendMsgToAllClients(msg); 
            } 
        } catch (InterruptedException ie) { 
            // Thread interrupted. Do nothing 
        } 
    } 
}