How to fix "no communication between server and client"

Question

This is code provided to me for a class. I am trying trying to fix a connection problem between the client and server. Even when both are started they do not connect.

This is for a Java based game of Battleship that will allow two users on separate devices to play one another. I'm not sure why the two do not connect and even the debugger has not been much help in directing me to the problem.

public class GameClient
{
    private Socket clientSocket;
    private PrintWriter out;
    private BufferedReader in;

    public void openConnection(String ip, int port)
    {
        try
        {
            clientSocket = new Socket(ip, port);
            out = new PrintWriter(clientSocket.getOutputStream(), true);
            in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

        }
        catch (Exception e)
        {
            System.out.println("Error opening client socket");
        }
    }

    public String sendMessage(String msg)
    {
        String resp = "";
        try
        {
            out.println(msg);
            resp = in.readLine();
        }
        catch (Exception e)
        {
            System.out.println("Error sending message from Client");
        }

        return resp;
    }

    public void stop()
    {
        try
        {
            in.close();
            out.close();
            clientSocket.close();
        }
        catch (Exception e)
        {
            System.out.println("Error stopping client");
        }
    }

    public static void main(String[] args)
    {
        GameClient client = new GameClient();

        client.openConnection("10.7.232.200", 3333);
        String response = client.sendMessage("1,2");
        System.out.println(response);
        client.stop();
    }
}

public class GameServer
{
    private ServerSocket serverSocket;
    private Socket clientSocket;
    private PrintWriter out;
    private BufferedReader in;

    public void start(int port)
    {
        try
        {
            serverSocket = new ServerSocket(port);
            clientSocket = serverSocket.accept();
            out = new PrintWriter(clientSocket.getOutputStream(), true);
            in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

            String move = in.readLine();

            System.out.println(move);

            out.println("6,1");

        }
        catch (Exception e)
        {
            System.out.println("Socket opening error");
        }

    }

    public void stop()
    {
        try
        {
            in.close();
            out.close();
            clientSocket.close();
            serverSocket.close();
        }
        catch (Exception e)
        {
            System.out.println("Error closing sockets");
        }
    }


    public static void main(String [] args)
    {
        GameServer server = new GameServer();
        server.start(3333);
        server.stop();
    }
}

public class PlayBattleship
{
    public static void main(String[] args)
    {
        GameClient client = new GameClient();

        client.openConnection("10.7.232.200", 3333);

        //System.out.println(response);


        BattleshipGame game = new BattleshipGame();

        while (!game.checkEndgame())
        {
            game.getGuess(client);
        }

        client.stop();
    }
}

The client and server should connect and stay connected till the game has reached completion EDIT: I have thoroughly read the API documentation but still cannot understand the problem.

Answer 1

The Server in your code isn't waiting for the incoming requests, it only serves a single incoming request and then kills itself due to the nature of the main method which starts it.

You need to have the server wait for the requests and do not die. Check the code snippet below to understand the logic.

Plus, always try to throw the exceptions if you can't do anything meaningful with it within the method it is caught in. In your code the main method of the server will anyway execute even if there is an exception caught in the start method

public class GameServer {
    private ServerSocket serverSocket;
    private Socket clientSocket;
    private PrintWriter out;
    private BufferedReader in;

    public ServerSocket start(int port) throws IOException {
        serverSocket = new ServerSocket(port);
        return serverSocket;
    }

    public void stop() throws IOException {
        in.close();
        out.close();
        clientSocket.close();
        serverSocket.close();
    }

    // This method accepts and serves the incoming requests
    public void acceptConnection(ServerSocket serverSocket) throws IOException {
        clientSocket = serverSocket.accept();
        out = new PrintWriter(clientSocket.getOutputStream(), true);
        in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

        String move = in.readLine();

        System.out.println(move);

        out.println("6,1");
    }

    public static void main(String[] args) throws IOException {
        GameServer server = new GameServer();
        ServerSocket serverSocket = server.start(3333);
        System.out.println("Server Started");

        // The effective change you need to make
        // Loop through the incoming requests
        while(true) {
            server.acceptConnection(serverSocket);
        }
    }
}


public class GameClient {
    private Socket clientSocket;
    private PrintWriter out;
    private BufferedReader in;

    public void openConnection(String ip, int port) throws IOException {
        clientSocket = new Socket(ip, port);
        out = new PrintWriter(clientSocket.getOutputStream(), true);
        in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
    }

    public String sendMessage(String msg) throws IOException {
        String resp = "";
        out.println(msg);
        resp = in.readLine();

        return resp;
    }

    public void stop() throws IOException {
        in.close();
        out.close();
        clientSocket.close();
    }

    public static void main(String[] args) throws IOException {
        GameClient client = new GameClient();

        client.openConnection("10.7.232.200", 3333);
        String response = client.sendMessage("1,2");
        System.out.println(response);
        client.stop();
    }
}