how to create multiple clients with single server in java socket programming?

Question

I am trying to follow the Java socket programming. My goal is to create multiple client threads, which post their state and all those are listened by the same server.

something like this 1. Server Started 2. Client A started 3. Client B started 4. Client A said "Hi" to Client B 5. Client B said "Hi" to Client A 6. Client A said "Hi2" to Client B 7. Client B said "Hi2" to Client A 8. Client A said "Hi3" to Client B 9. Client B said "Hi3" to Client A 10. Client A completed 11. Client B completed

what I have tried so far is :

1. MyServer.java

import java.net.*;
import java.io.*;

class MyServer
{
    public static void main(String args[]) throws Exception
    {
        ServerSocket server_socket = new ServerSocket(3333);
        Socket client_socket = server_socket.accept();
        DataInputStream din = new DataInputStream(client_socket.getInputStream());
        DataOutputStream dout = new DataOutputStream(client_socket.getOutputStream());
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        String str = "", str2 = "";
        int counter = 0;
        while (!str.equals("stop") && counter < 10)
        {
            str = din.readUTF();
            System.out.println("client says: " + str);
            //str2 = br.readLine();
            str2 = str +"server response ";
            dout.writeUTF(str2);
            dout.flush();
            counter ++;
        }

        din.close();
        client_socket.close();
        server_socket.close();
    }
}

2. MyClient.java

import java.util.stream.IntStream;

public class ClientThread implements Runnable
{
String client_name;

public ClientThread(String client_name)
{
    this.setClient_name(client_name);
}

public void run()
{
    for(int i=0;i<5;i++)
    {
        System.out.println(this.getClient_name()+" : "+i);
        new ClientHelper().sendMessageToServer(this.getClient_name(),i);
        try
        {
            Thread.sleep(1000);
        } catch (InterruptedException e)
        {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

public String getClient_name()
{
    return client_name;
}

private void setClient_name(String client_name)
{
    this.client_name = client_name;
}

}

3 . ClientHelper.java

import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.Socket;
import java.net.UnknownHostException;

public class ClientHelper
{
    Socket socket;
    DataInputStream din ;
    DataOutputStream dout ;

    public void sendMessageToServer(String player_name, int i)
    {
        try
        {
            socket = new Socket("localhost", 3333);
            din = new DataInputStream(this.getSocket().getInputStream());
            dout = new DataOutputStream(this.getSocket().getOutputStream());
            // BufferedReader br = new BufferedReader(new
            // InputStreamReader(System.in));
            dout.writeUTF(player_name + " : says hi :" + i);
            dout.flush();
            socket.close();
        } catch (UnknownHostException e )
        {
            e.printStackTrace();
        } catch (IOException e)
        {
            e.printStackTrace();
        } finally
        {
        }

    }

    private Socket getSocket()
    {
        return socket;
    }

    private void setSocket(Socket socket)
    {
        this.socket = socket;
    }
}

4. App.java

public class App 
{

    public static void main( String[] args )
    {
        new Thread(new ClientThread("A")).start();
        //new Thread(new ClientThread("B")).start();
        /*try
        {

            DataInputStream dataInputStream;
            DataOutputStream dataOutputStream;
            BufferedReader bufferedReader; 
            Socket socket = new Socket("localhost", 12345);
            dataInputStream = new DataInputStream(socket.getInputStream());
            dataOutputStream = new DataOutputStream(socket.getOutputStream());
            bufferedReader = new BufferedReader(new InputStreamReader(System.in));

            Player p1 = new Player("p1", dataInputStream, dataOutputStream, bufferedReader);
            Player p2 = new Player("p2", dataInputStream, dataOutputStream, bufferedReader);
            p1.move();
            p2.move();
        } catch (UnknownHostException e)
        {
            e.printStackTrace();
        } catch (IOException e)
        {
            e.printStackTrace();
        }*/

    }
}

It connects one client, but second client does not connect.

Answer 1

Your MyServer is wrong. It accepts just one client.

    try (ServerSocket s = new ServerSocket(...);) {
        while (true) {
            Socket conn = s.accept();
            conn.getInetAddress().getHostName() + " : " + conn.getPort());
            new ServerConnection(conn).start();
        }
    }
    catch(IOException e) {
        e.printStackTrace();
    }

}

and for each client something like this

public class ServerConnection extends Thread {

    private Socket client_socket;

    public ServerConnection( Socket client_socket) {
        this.client_socket = client_socket;
    }

    public void run() {
        DataInputStream din = new DataInputStream(client_socket.getInputStream());
        DataOutputStream dout = new DataOutputStream(client_socket.getOutputStream());
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        String str = "", str2 = "";
        int counter = 0;
        while (!str.equals("stop") && counter < 10)
        {
            str = din.readUTF();
            System.out.println("client says: " + str);
            //str2 = br.readLine();
            str2 = str +"server response ";
            dout.writeUTF(str2);
            dout.flush();
            counter ++;
        }

        din.close();
    }
}