send a message to specific client threads

Question

I have this Server class,

import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;

public class Server {
    public static ArrayList<String> waiting = new ArrayList<String>();
    public static ArrayList<String> playing = new ArrayList<String>();
    public static ArrayList<Integer> score = new ArrayList<Integer>();

    public static void main(String[] args) {
        try {
            ServerSocket server = new ServerSocket(4321);
            while (true) {
                try {
                    Socket socket = server.accept();
                    new EchoThread(socket).start();
                } catch (Exception exc) {
                    exc.printStackTrace();
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void addClient(String name) {
        waiting.add(name);
    }

    public int getNumClients() {
        return waiting.size();
    }

    public String getClientName(int i) {
        return waiting.get(i);
    }

    public void play() {
        int scr = 0;
        for (int i = 0; i < 4; i++) {
            playing.add(waiting.get(0));
            score.add(scr);
            waiting.remove(0);
        }
    }

    public boolean checkIfPlaying(String name) {
        if (playing.indexOf(name) >= 0) {
            return true;
        } else {
            return false;
        }
    }
}

and the Thread Class,

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.Socket;

public class EchoThread extends Thread {
    protected Socket socket;

    public EchoThread(Socket clientSocket) {
        this.socket = clientSocket;
    }

    public void run() {
        Server s = new Server();
        DataInputStream in = null;
        DataOutputStream out = null;
        String line;

        try {
            in = new DataInputStream(socket.getInputStream());
            out = new DataOutputStream(socket.getOutputStream());
        } catch (IOException e) {
            return;
        }

        while (true) {
            try {
                line = in.readLine();
                String[] prot = line.split(":");

                if (prot[0].equals("/login")) {
                    s.addClient(prot[1]);
                } else if (prot[0].equals("/waiting")) {
                    if (s.checkIfPlaying(prot[1])) {
                        out.writeBytes("Playing" + "\r\n");
                    } else {
                        if (s.getNumClients() >= 4) {
                            s.play();
                            out.writeBytes("Playing" + "\r\n");
                        } else {
                            out.writeBytes(s.getNumClients() + "\r\n");
                        }
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
                return;
            }
        }
    }
}

If the client connect to the server, the name of the client is stored in Server Class Array, waiting. If the waiting clients is equals to 4, it will remove from the waiting array and put it in playing array.

I would like to make the server send message to the first 4 clients in playing array.

How can I do it?

Answer 1

For your Server Class, I would change your ArrayList< String > for waiting and playing to ArrayList< EchoThread >. This way your Server class is tracking each client object themselves instead of just their names. When you instantiate your EchoThread objects, I would pass the local server object to each EchoThread that way each object knows about the server that instantiated them.

Server Class

import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;

public class Server {
    public ArrayList<EchoThread> waiting = new ArrayList<EchoThread>();
    public ArrayList<EchoThread> playing = new ArrayList<EchoThread>();
    public ArrayList<Integer> score = new ArrayList<Integer>();

    public static void main(String[] args) {
        try {
            // Instantiate a single server object that you can pass into your connected clients
            Server myServer = new Server();
            ServerSocket server = new ServerSocket(4321);
            while (true) {
                try {
                    Socket socket = server.accept();
                    // Pass myServer into Echo Thread 
                    new EchoThread(myServer, socket).start();
                } catch (Exception exc) {
                    exc.printStackTrace();
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // Have to synchronize this since multiple clients could be adding to this list at the same time
    public synchronized void addClient(EchoThread client) {
        waiting.add(client);
    }

    public int getNumClients() {
        return waiting.size();
    }

    public String getClientName(int i) {
        return waiting.get(i).getCName();
    }

    public void play() {
        int scr = 0;
        for (int i = 0; i < 4; i++) {
            EchoThread clientBeingMovedToPlaying = waiting.get(0);
            playing.add(clientBeingMovedToPlaying);
            score.add(scr);
            waiting.remove(0);

            // This will be a new method in your EchoThread class
            clientBeingMovedToPlaying.SendServerPlayingMessage();
        }
    }

    public boolean checkIfPlaying(String name) {
        boolean isPlaying = false;
        for(EchoThread client : playing) {
            if (client.getName().contentEquals(name)) {
                isPlaying = true;
                break;
            }
        }
        return isPlaying;
    }
}

For your Echo Thread class, I would make your variables in your run method class variables so they can be used throughout the class

EchoThread Class

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.Socket;

public class EchoThread extends Thread {
    protected Socket socket;
    protected Server s;
    protected DataInputStream in;
    protected DataOutputStream out;
    protected String line;
    protected String clientName;

    // This way, each EchoThread object knows about the server
    public EchoThread(Server theServer, Socket clientSocket) {
        this.s = theServer;
        this.socket = clientSocket;
    }

    public void run() {
        try {
            in = new DataInputStream(socket.getInputStream());
            out = new DataOutputStream(socket.getOutputStream());
        } catch (IOException e) {
            return;
        }

        while (true) {
            try {
                line = in.readLine();
                String[] prot = line.split(":");

                if (prot[0].equals("/login")) {
                    // Original code
                    //s.addClient(prot[1]);

                    // New code
                    clientName = prot[1];
                    s.addClient(this);
                } else if (prot[0].equals("/waiting")) {
                    if (s.checkIfPlaying(prot[1])) {
                        out.writeBytes("Playing" + "\r\n");
                    } else {
                        // You don't want multiple clients firing the play method, so you need to synchronize your server object
                        synchronized (s) {
                            if (s.getNumClients() >= 4) {
                                s.play();
                                out.writeBytes("Playing" + "\r\n");
                            } else {
                                out.writeBytes(s.getNumClients() + "\r\n");
                            }
                        }
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
                return;
            }
        }
    }

    public String getCName() {
        return clientName;
    }

    public void SendServerPlayingMessage() {
        if (out != null) {
            // Send whatever message you want
        }
    }
}

I think this'll get you what your wanting... Forgive any syntax or logical errors, I don't have an IDE right in front of me at the moment.