SasalaMulticastSender.java

import java.io.*;
import java.net.*;
import java.time.LocalDateTime;

/**
 * Looks a lot like a UDP sender.
 * 
 * @author mcgredo
 */
public class SasalaMulticastSender {

    public static final String MULTICAST_ADDRESS = "239.1.2.15";
    public static final int DESTINATION_PORT = 1717;
    /** How many routers can be crossed */
    public static final int TTL = 10; 
    
    public static void main(String[] args) 
    {
        try
        {
            // This is a java/IPv6 problem. You should also add it to the
            // arguments used to start the app, eg -Djava.net.preferIPv4Stack=true
            // set in the "run" section of preferences. Also, typically
            // netbeans must be restarted after these settings.
            // https://stackoverflow.com/questions/18747134/getting-cant-assign-requested-address-java-net-socketexception-using-ehcache
            System.setProperty("java.net.preferIPv4Stack", "true");
            
            
            MulticastSocket multicastSocket = new MulticastSocket(1718);
            multicastSocket.setTimeToLive(TTL);
            InetAddress multicastAddress = InetAddress.getByName(MULTICAST_ADDRESS);
            System.out.println(multicastAddress);            
            // Join group useful on receiving side
            multicastSocket.joinGroup(multicastAddress);
            // You can join multiple groups here
            
            // Put together a message with binary content. "ByteArrayOutputStream"
            // is a java.io utility that lets us put together an array of binary
            // data, which we put into the UDP packet.
            
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            DataOutputStream dos = new DataOutputStream(baos);
            
            for(int idx = 0; idx < 100; idx++)
            {
                double temperature = 100 * Math.random();
                LocalDateTime LDT =  LocalDateTime.now();
                String time = LDT.toString();
            
                dos.writeFloat((float) temperature);
                dos.writeChars(time);
            
                // Put together a packet to send
                // muticast group we are sending to--not a single host
                byte[] buffer = baos.toByteArray();
                DatagramPacket packet = new DatagramPacket(buffer, buffer.length, multicastAddress, DESTINATION_PORT);
                
                multicastSocket.send(packet);
                Thread.sleep(1000); // Send 100, one per second
                System.out.println("Sent multicast packet " + idx + " of 100");
                
                baos.reset();
            }
        }
        catch(Exception e)
        {
            System.out.println(e);
        }
    }
    
}