Question

I’ve followed a tutorial to create the socket server below which allows multiple users to connect and if they send some data to it then it returns it back to them.

   import java.awt.Color;
    import java.awt.BorderLayout;
    import java.awt.event.*;
    import javax.swing.*;

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

    class ClientWorker implements Runnable {
      private Socket client;
      private JTextArea textArea;

      ClientWorker(Socket client, JTextArea textArea) {
       this.client = client;
       this.textArea = textArea;   
      }

      public void run(){
        String line;
        BufferedReader in = null;
        PrintWriter out = null;
        try{
          in = new BufferedReader(new InputStreamReader(client.getInputStream()));
          out = new PrintWriter(client.getOutputStream(), true);
        } catch (IOException e) {
          System.out.println("in or out failed");
          System.exit(-1);
        }

        while(true){
          try{
            line = in.readLine();
    //Send data back to client
             out.println(line);
             textArea.append(line);
           } catch (IOException e) {
             System.out.println("Read failed");
             System.exit(-1);
           }
        }
      }
    }



----------


    class SocketThrdServer extends JFrame{

       JLabel label = new JLabel("Text received over socket:");
       JPanel panel;
       JTextArea textArea = new JTextArea();
       ServerSocket server = null;

       SocketThrdServer(){ //Begin Constructor
         panel = new JPanel();
         panel.setLayout(new BorderLayout());
         panel.setBackground(Color.white);
         getContentPane().add(panel);
         panel.add("North", label);
         panel.add("Center", textArea);
       } //End Constructor

      public void listenSocket(){
        try{
          server = new ServerSocket(4444); 
        } catch (IOException e) {
          System.out.println("Could not listen on port 4444");
          System.exit(-1);
        }
        while(true){
          ClientWorker w;
          try{
            w = new ClientWorker(server.accept(), textArea);
            Thread t = new Thread(w);
            t.start();
          } catch (IOException e) {
            System.out.println("Accept failed: 4444");
            System.exit(-1);
          }
        }
      }

      protected void finalize(){
    //Objects created in run method are finalized when 
    //program terminates and thread exits
         try{
            server.close();
        } catch (IOException e) {
            System.out.println("Could not close socket");
            System.exit(-1);
        }
      }

      public static void main(String[] args){
            SocketThrdServer frame = new SocketThrdServer();
        frame.setTitle("Server Program");
            WindowListener l = new WindowAdapter() {
                    public void windowClosing(WindowEvent e) {
                            System.exit(0);
                    }
            };
            frame.addWindowListener(l);
            frame.pack();
            frame.setVisible(true);
            frame.listenSocket();
      }
    }

However I need it so if data is sent to the server rather than simply returning it, it sends it to everyone who is connected to the server. If someone helps me sort this out then ill be forever thankful! It means ill be able to finish my School project!

Thanks in advance 🙂

Answer 1

This is your problem:

//Send data back to client
out.println(line);

As the others have said, use a List to keep track of all your clients.
Specifically, you want a List of ClientWorkers.

I use a simple Singleton class that keeps the List. This is so that when a new client connects it will add itself to the list and the other clients don’t need to do anything to see that there is a new client. And add a method like writeString(String) to the ClientWorker class to make it easier to write something out to each client.

You should have a really basic loop like this in ClientWorker:

String line = in.readLine();
LinkedList<ClientWorkers> clients = SingletonClients.getClients();
for(int = 0; i < clients.size(); i++) {
    ClientWorker c = clients.get(i);
    //The client doesn't need to get it's own data back.
    if(c == this)
        continue;

    c.writeString(line);
}

writeString will just be:

public void writeString(String s) {
    try {
        out.println(s);
    } catch(IOException ex) {
    }
}