UDP Unicast Communication between three servers using java

Question

I want to make three servers communicate using java UDP. If a particular method which exists for all the three servers is called on the first server instance the other two servers should also communicate the result for those methods to the first servers using UDP. Should I be using multicast ? I tried using Unicast but its not working out.

UDPDataExchangeclass

import java.io.BufferedReader;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.SocketTimeoutException;
import java.net.UnknownHostException;

public class UDPDataExchange {

    String              Hostname;
    static InetAddress  IPAddress;

    UDPDataExchange() {
        Hostname = new String("127.0.0.1");
        try {
            IPAddress = InetAddress.getByName(Hostname);
        }
        catch (UnknownHostException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public void requestData(int portNumber, String data) {
        try {
            DatagramSocket clientSocket = new DatagramSocket();
            byte[] receiveData = new byte[1024];
            DatagramPacket receivePacket = new DatagramPacket(receiveData,
                    receiveData.length);
            byte[] sendData = new byte[1024];
            sendData = data.getBytes();
            System.out.print("Ready to send data ");
            DatagramPacket sendPacket = new DatagramPacket(sendData,
                    sendData.length, IPAddress, portNumber);
            clientSocket.send(sendPacket);
            clientSocket.setSoTimeout(10000);
            try {
                clientSocket.receive(receivePacket);
                String modifiedSentence = new String(receivePacket.getData());

                InetAddress returnIPAddress = receivePacket.getAddress();

                int port = receivePacket.getPort();

                System.out.println("From server at: " + returnIPAddress + ":"
                        + port);
                System.out.println("Message: " + modifiedSentence);

            }
            catch (SocketTimeoutException ste) {
                System.out.println("Timeout Occurred: Packet assumed lost");
            }
            //clientSocket.close();

        }
        catch (SocketException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

    public void responseData(int portNumber) {
            try {

                DatagramSocket serverSocket = new DatagramSocket(portNumber);
                byte[] receiveData = new byte[1024];
                byte[] sendData = new byte[1024];

                while (true) {

                    receiveData = new byte[1024];

                    DatagramPacket receivePacket = new DatagramPacket(receiveData,
                            receiveData.length);

                    System.out.println("Waiting for datagram packet");

                    serverSocket.receive(receivePacket);

                    String sentence = new String(receivePacket.getData());

                    InetAddress IPAddress = receivePacket.getAddress();

                    int port = receivePacket.getPort();

                    System.out.println("From: " + IPAddress + ":" + port);
                    System.out.println("Message: " + sentence);

                    String capitalizedSentence = sentence.toUpperCase();

                    sendData = capitalizedSentence.getBytes();

                    DatagramPacket sendPacket = new DatagramPacket(sendData,
                            sendData.length, IPAddress, port);

                    serverSocket.send(sendPacket);

                }

            }
            catch (SocketException ex) {
                System.out.println("UDP Port 9876 is occupied.");
                System.exit(1);
            }
            catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

    }


}

UDPTest

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

class UDPTest extends UDPDataExchange {

    public static void main(String args[]) throws Exception {
        int UDPClientConcordiaPortNumber = 9876;
        int UDPClientMcgillPortNumber=9890;
        int UDPClientDawsonPortNumber=9891;
        UDPTest McgillServer=new UDPTest();
        UDPTest DawsonServer=new UDPTest();
        McgillServer.responseData(UDPClientConcordiaPortNumber);
        DawsonServer.responseData(UDPClientDawsonPortNumber);

        UDPTest concordiaTest = new UDPTest();

        System.out.println("Attemping to connect to " + IPAddress
                + ") via UDP port" + UDPClientConcordiaPortNumber);

        String concordiaData = "Hello from concordia";
        System.out.println("Sending data  " + concordiaData.length()
                + " bytes to server.");

        concordiaTest.requestData(UDPClientConcordiaPortNumber, concordiaData);

    }
}

In the UDPDataExchange I've defined two methods to send and receive data. In the UDPTest class I am trying to create two server instances namely mcgill and dawson server who would listen to concordia's port for data sent. Once they receive it they send a response back to Concordia

Answer 1

Try this, I´m not sure if it is exactly what you want.

UDPDataExchange

public class UDPDataExchange {

String Hostname;
static InetAddress IPAddress;

UDPDataExchange() {
    Hostname = new String("127.0.0.1");
    try {
        IPAddress = InetAddress.getLocalHost();
    } catch (final UnknownHostException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

public void requestData(final int portNumber, final String data) {
    try {
        final DatagramSocket clientSocket = new DatagramSocket();
        final byte[] receiveData = new byte[1024];
        final DatagramPacket receivePacket = new DatagramPacket(receiveData,
                receiveData.length);
        byte[] sendData = new byte[1024];
        sendData = data.getBytes();
        System.out.print("Ready to send data ");
        final DatagramPacket sendPacket = new DatagramPacket(sendData,
                sendData.length, IPAddress, portNumber);
        clientSocket.send(sendPacket);
        clientSocket.setSoTimeout(10000);
        try {
            clientSocket.receive(receivePacket);
            final String modifiedSentence = new String(receivePacket.getData());

            final InetAddress returnIPAddress = receivePacket.getAddress();

            final int port = receivePacket.getPort();

            System.out.println("From server at: " + returnIPAddress + ":"
                    + port);
            System.out.println("Message: " + modifiedSentence);

        } catch (final SocketTimeoutException ste) {
            System.out.println("Timeout Occurred: Packet assumed lost");
        }
        // clientSocket.close();

    } catch (final SocketException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (final IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

public void responseData(final int portNumber) {
    try {

        final DatagramSocket serverSocket = new DatagramSocket(portNumber, IPAddress);
        byte[] receiveData = new byte[1024];
        byte[] sendData = new byte[1024];

        while (true) {

            receiveData = new byte[1024];

            final DatagramPacket receivePacket = new DatagramPacket(receiveData,
                    receiveData.length);

            System.out.println("Waiting for datagram packet");

            serverSocket.receive(receivePacket);

            final String sentence = new String(receivePacket.getData());

            final InetAddress IPAddress = receivePacket.getAddress();

            final int port = receivePacket.getPort();

            System.out.println("From: " + IPAddress + ":" + port);
            System.out.println("Message: " + sentence);

            final String capitalizedSentence = sentence.toUpperCase();

            sendData = capitalizedSentence.getBytes();

            final DatagramPacket sendPacket = new DatagramPacket(sendData,
                    sendData.length, IPAddress, port);

            serverSocket.send(sendPacket);

        }

    } catch (final SocketException ex) {
        System.out.println("UDP Port 9876 is occupied.");
        System.exit(1);
    } catch (final IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

}

UDPTest

class UDPTest extends UDPDataExchange {

public static void main(final String args[]) throws Exception {
    final int UDPClientConcordiaPortNumber = 9876;
    final int UDPClientMcgillPortNumber = 9890;
    final int UDPClientDawsonPortNumber = 9891;
    final UDPTest McgillServer = new UDPTest();
    final UDPTest DawsonServer = new UDPTest();
    final Thread t1 = new Thread() {
        @Override
        public void run() {
            McgillServer.responseData(UDPClientMcgillPortNumber);
        }
    };
    t1.setDaemon(true);
    t1.start();
    final Thread t2 = new Thread() {
        @Override
        public void run() {
            DawsonServer.responseData(UDPClientDawsonPortNumber);
        }
    };
    t2.setDaemon(true);
    t2.start();

    final UDPTest concordiaTest = new UDPTest();

    System.out.println("Attemping to connect to " + IPAddress
            + ") via UDP port" + UDPClientConcordiaPortNumber);

    final String concordiaData = "Hello from concordia";
    System.out.println("Sending data  " + concordiaData.length()
            + " bytes to server.");

    concordiaTest.requestData(UDPClientMcgillPortNumber, concordiaData);
    concordiaTest.requestData(UDPClientDawsonPortNumber, concordiaData);

}

}

I´ll explain brielfy what I changed:

UDPDataExchange: I changed the IPAdress to InetAddress.getLocalHost()

UDPTest: Each call to responseData runs in a separate Thread, to avoid blocking the main thread. That threads are daemon to allow exit application. The requestData() invocation has changed to call each server.

Hope to be useful.