Client / Server / Client Communication via sockets

Question

I have 3 devices which are connected via a bluetooth PAN network.

• Device 1: Server - The Server is in my case an EV3 LEGO Brick == a ROBOT!
• Device 2: Remote - The second device (Android APP) should be used to control the actions of the Device 1
• Device 3: Frontend - The third device should display the chosen actions (Android)

The possible communication method is bluetooth and a socket connection in JAVA. I can already control DEVICE 1 from DEVICE 2 - but the commands are not relayed to DEVICE 3. This is the code which I am using for my server:

Main

        try {
        serverSocket = new ServerSocket( 1111 );
    } catch (IOException e) {
        e.printStackTrace();

    }
    while (true) {
        try {
            socket = serverSocket.accept();
        } catch (IOException e) {
            System.out.println("I/O error: " + e);
        }
        // new thread for a client
        new RelayThread(socket).start();
    }

RelayThread THREAD

public class RelayThread extends Thread {
protected Socket socket;
BufferedReader bufferedReader;

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

public void run() {
    Singleton motors = Singleton.getInstance();
    InputStream inp = null;
    BufferedReader brinp = null;
    DataOutputStream out = null;
    try {
        inp = socket.getInputStream();
        InputStreamReader isr = new InputStreamReader(inp, "UTF-8");
        bufferedReader = new BufferedReader(isr);           

        out = new DataOutputStream(socket.getOutputStream());
    } catch (IOException e) {
        return;
    }
    while (true) {
        try {
            String command= bufferedReader.readLine();
            if ((command== null) || command.equalsIgnoreCase("QUIT")) {
                socket.close();
                return;
            } 
            else {
              // do ROBOT actions

                /*
                 * SERVER ACTIONS
                 */
                    // notify the other client of the delivered LINE
                    out.writeBytes(command);
                    out.flush();
                }
            } catch (IOException e) {
                e.printStackTrace();
                return;
            }
        }
    }
}

I'm using TCP-Client as my DEVICE 3 right now - but it doesn't show any text when I send commands via DEVICE 2. How could I realize my project - and what am I doing wrong?

Answer 1

this is for your server. Creating a list of all connections

List<RelayThread> clients = new ArrayList<RelayThread>();
while (true) {
        try {
            socket = serverSocket.accept();
        } catch (IOException e) {
            System.out.println("I/O error: " + e);
        }
        // new thread for a client
        RelayThread relay = new RelayThread(socket,this);
        relay.start();
        clients.add(relay); 
   }

and a method to send message to other clients

public void sendCommand(String command, RelayThread source){
  for (int i=0;i<clients.size();i++){
     if (clients.get(i) != source) {
        clients.get(i).sendCommand(command);
     }
  }
}

and, constructor of RelayThread to keep Main

Main main;
public RelayThread (Socket clientSocket,Main main) {
    this.socket = clientSocket;
    this.main = main;
}

and, a sender message in RelayThread

public void sendCommand(String command){
    out.writeBytes((command+"\r\n").getBytes()); // I suggest you add a parser charachter, like \r\n. then client can understand message ends
}