Thread: Client and server socket conection - how to send IDs to clients

it looks like the code player_number = Integer.parseInt(inputLine); is called too soon and the server doesn't send the ID by the time, and that's why it freezes i guess. I put output1.println("1"); in a while(true) loop and it worked

Can you make a small, complete program that compiles, executes and shows the problem?

How small? Because there's pretty much nothing left except imports, definitions and constructors plus the code I already posted.

Client:

 import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.net.*;
import java.util.*;
 
import javax.swing.*;
 
public class Client extends JFrame implements ActionListener{
        private static Socket conn;
        private static JTextArea TA;
        private static JTextField TF;
        private JPanel panel1;
        private final static int port = 1234;
        private ArrayList<Ship> myShips = new ArrayList();
        static PrintWriter out;
        static BufferedReader in;
        static int player_number = 1;
 
        public Client() {
                super("Client");
                setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                setSize(new Dimension(400, 300));
                Container c = getContentPane();
                c.setBackground(Color.BLACK);
                TA = new JTextArea();
                TA.setEditable(false);
                TA.setBackground(Color.BLACK);
                TA.setForeground(Color.WHITE);
                c.add(new JScrollPane(TA));
                TF = new JTextField();
                TF.setEditable(true);
                TF.setBackground(Color.BLACK);
                TF.setForeground(Color.WHITE);
                c.add(TF, BorderLayout.SOUTH);
                setVisible(true);
                TF.addActionListener(this);
                TA.append("Client started.\n");
        }
 
        public static void main(String[] args) {
 
                new Client();
                try {
                        connect();
 
                } catch (IOException e) {
                        e.printStackTrace();
                }// catch
 
        }
 
        private static void connect() throws IOException {
                conn = new Socket("192.168.0.25", port);
                TA.append("Socket created.\n");
                out = new PrintWriter(conn.getOutputStream(), true);
                in = new BufferedReader(new InputStreamReader(conn.getInputStream()));
                TA.append("Streams created.\n");
                String inputLine;
                inputLine = in.readLine();
                if(inputLine == null)
                        System.out.println("null");
                player_number = Integer.parseInt(inputLine);
                TA.append("Your ID is " + player_number + " .");
        }
 
        public void actionPerformed(ActionEvent evt) {
                String text = TF.getText();
                TA.append("Me: " + text + "\n");
                TF.selectAll();
                TA.setCaretPosition(TA.getDocument().getLength());
                if (player_number == 2)
                        try {
                                TA.append("Player 1: " + in.readLine());
                        } catch (IOException e1) {
                                e1.printStackTrace();
                        }
                out.println(text);
                if (player_number == 1)
                        try {
                                TA.append("Player 2: " + in.readLine());
                        } catch (IOException e1) {
                                e1.printStackTrace();
                        }
 
        }
 
}

Server:

import java.awt.*;
import java.io.*;
import java.net.*;
import java.util.ArrayList;
 
import javax.swing.*;
 
public class Server extends JFrame {
        private ServerSocket server;
        private Socket conn1;
        private Socket conn2;
        private JTextArea TA;
        private JPanel panel1;
        private int port = 1234;
        PrintWriter output1;
        BufferedReader input1;
        PrintWriter output2;
        BufferedReader input2;
 
 
        public Server() {
                super("Server");
                setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                setSize(new Dimension(400, 300));
                Container c = getContentPane();
                c.setBackground(Color.BLACK);
                TA = new JTextArea();
                TA.setEditable(true);
                TA.setBackground(Color.BLACK);
                TA.setForeground(Color.GREEN);
                c.add(new JScrollPane(TA));
                setVisible(true);
                TA.append("Server started.\n");
        }
 
        public void start() {
                try {
 
                        connect();
                } catch (IOException ioe) {
                        System.out.println(ioe);
                } catch (InterruptedException e) {
                        e.printStackTrace();
                }
        }
 
        public void log(final JTextArea txt, final String message) {
                SwingUtilities.invokeLater(new Runnable() {
                        public void run() {
                                txt.append(message);
                        }
                });
        }
 
        public void connect() throws IOException, InterruptedException {
                log(TA, "ServerSocket created. \nListering for connections...\n");
                server = new ServerSocket(port, 2);
 
                conn1 = server.accept();
                output1 = new PrintWriter(conn1.getOutputStream());
                input1 = new BufferedReader(new InputStreamReader(
                                conn1.getInputStream()));
                log(TA, "User " + 1 + " connected.\n");
                Thread.sleep(10000);
                        output1.println("1");
 
 
                conn2 = server.accept();
                output2 = new PrintWriter(conn2.getOutputStream());
                input2 = new BufferedReader(new InputStreamReader(
                                conn2.getInputStream()));
                log(TA, "User " + 2 + " connected.\n");
                output2.println("2");
                while (true) {
                        String text = input1.readLine();
 
                        TA.append("Player 1: " + text + "\n");
                        output2.println("Player 1: " + text);
 
                        text = input2.readLine();
 
                        TA.append("Player 2: " + text + "\n");
                        output1.println("Player 2: " + text);
                }
 
        }
}

and this to run the server:

public class ServerLauncher {
 
	public static void main(String[] args) {
	    Server s = new Server();
	    s.start();
	}
 
}

See my edit above, the code to send ID to 1st client works when I put it in endless loop so i guess it's a synchronization issue between server sending the ID and client trying to read it.

Please post the code here, not as links to other sites.

There are missing class definitions.

How are you debugging the code? I don't see anything printed on the console when the code executes.

One possible problem I see is that there are several if statements that do NOT enclose the following code in {}s. That is dangerous and will create errors when the code is changed.

Try flushing the output after writing to it to push the data out of any buffers.

I debug client server apps by running them in one jvm so all output goes to one console so the order of events is easy to see.
Here is the code I use:

   public static void main(String[] args) {
      Thread t1 = new Thread(new Runnable() {
         public void run() {
   	    Server s = new Server();
	       s.start();
         }
      });
      t1.start();
 
      try{Thread.sleep(100);}catch(Exception x){}
 
      Thread t2 = new Thread(new Runnable() {
         public void run() {
            try{Client.main(new String[]{"127.0.0.1", "8080"});}catch(Exception x){x.printStackTrace();}
         }
      });
      t2.start();
 
      Thread t3 = new Thread(new Runnable() {
         public void run() {
            try{Client.main(new String[]{"127.0.0.1", "8080"});}catch(Exception x){x.printStackTrace();}
         }
      });
      t3.start();
 
      // wait some and exit   in case app freezes
      try{Thread.sleep(30000);}catch(Exception x){}
      System.out.println("Exiting main");
      System.exit(0);
   }

For this to work, all static variables need to be changed to be instance variables.

Thank you, the debug code really helped. I put system messages after every step in debugger, server and client and this is the output:

Debugger: Starting server.
Server: Constructor running.
Server: GUI created.
Server: setting up connections.
Server: serversocket created.
Debugger: Starting client 1..
Client: Constructor running.
Client: connecting to server.
Server: connection 1 accepted.
Client: Socket created.
Server: output1 opened.
Client: output stream opened.
Server: input1 opened.
Server: ID 1 sent.
Client: input stream opened.
Client: Waiting for ID.
Debugger: Starting client 2..
Client: Constructor running.
Client: connecting to server.
Server: connection 2 accepted.
Client: Socket created.
Server: output2 opened.
Client: output stream opened.
Server: input2 opened.
Server: ID 2 sent.
Server: conversation started.
Client: input stream opened.
Client: Waiting for ID.
Exiting main

I have a feeling that clients should start listening for IDs before server sends them, right? How can I change it or delay ID sending on server side?


edit:

to further test this, I ran server side ID sending in a loop

int i = 1;
while(true)
{
output1.println("1");
if(i ==0)
     break;
if(i%1000==0)
     System.out.println(i + " Server: ID 1 sent.");
i++;
}

And from the output on console i see that server sends ID between 5000 and 6000 times before client accepts it.

...
Client: Waiting for ID.
1000 Server: ID 1 sent.
2000 Server: ID 1 sent.
3000 Server: ID 1 sent.
4000 Server: ID 1 sent.
5000 Server: ID 1 sent.
Client: Received ID 1 .              <--
6000 Server: ID 1 sent.
...
73000 Server: ID 1 sent.
Debugger: Starting client 2..
Client: Constructor running.
Client: connecting to server.
Client: Socket created.
Client: output stream opened.
Client: input stream opened.
Client: Waiting for ID.
Exiting main

I tried to do the same for the 2nd ID but it doesn't work, the client doesnt respond with "Received ID 2"

Another problem is doing potentially long running code from a listener. The listener runs on the EDT which is where the JVM executes to update the GUI. The long running code should be done on its own thread.

There is an example of how to use threads in post#12. It starts 3 threads to run the server and clients.
Put the code that does the reading inside a thread