Network Programming Multicast Socket (NPMS)

Instructional Objectives

After participating in this practicum, students are expected to be able to:

1. Understanding about multicast Socket.
2. Able to create simple programs.

1. Multicast Socket

Multicasting is broader than unicast, multicasting sends data from one host to a different host, but not to everyone, the data only goes to clients who have stated to join a particular multicast group.

In Java, data multicasting uses the java.net.MulticastSocket class, a subclass of java.net.DatagramSocket. MulticastSocket's behavior is very similar to DatagramSocket's. You put your data in a DatagramPacket object that you send and receive with MulticastSocket. The constructor throws a SocketException if the Socket cannot be created. For example:

try {  
    MulticastSocket ms = new MulticastSocket( );
 // send some datagrams... 
 } catch (SocketException se) { 
     System.err.println(se);
 } 

2. Example Program

MulticastSniffer.java

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

 public class MulticastSniffer {

    public static void main(String[] args) {
        InetAddress group = null;
        int port = 0;
        try {
            group = InetAddress.getByName(args[0]);
            port = Integer.parseInt(args[1]);
        } catch (Exception ex) {
            System.err.println( "Usage: java MulticastSniffer multicast_address port");
            System.exit(1);
        } 
        
        MulticastSocket ms = null;
 
        try {
            ms = new MulticastSocket(port);
            ms.joinGroup(group);
            byte[] buffer = new byte[8192];
            while (true) {
                DatagramPacket dp = new DatagramPacket(buffer, buffer.length);
                ms.receive(dp);
                String s = new String(dp.getData( ));
                System.out.println(s);
            } 
        } catch (IOException ex) {
            System.err.println(ex);
        } finally {
            if (ms != null) {
        try {
            ms.leaveGroup(group);
            ms.close( );
        } catch (IOException ex) {
        } 
    } 
    } 
    } 
    
}

MulticastSender.java

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

public class MulticastSender {

 public static void main(String[] args) {
    InetAddress ia = null;
    int port = 0;
    byte ttl = (byte) 1;

    try {
        ia = InetAddress.getByName(args[0]);
        port = Integer.parseInt(args[1]);
        if (args.length > 2) ttl = (byte) Integer.parseInt(args[2]);
    } catch (Exception ex) {
        System.err.println(ex);
        System.err.println( "Usage: java MulticastSender multicast_address port ttl");
        System.exit(1);
    } 
    
    byte[] data = "Here's some multicast data\r\n".getBytes( );
    DatagramPacket dp = new DatagramPacket(data, data.length, ia, port);

    try {
        MulticastSocket ms = new MulticastSocket( );
        ms.joinGroup(ia);
        for (int i = 1; i < 10; i++) {
            ms.send(dp, ttl);
        } 

    ms.leaveGroup(ia);
    ms.close( );

    } catch (SocketException ex) {
        System.err.println(ex);
    } catch (IOException ex) {
        System.err.println(ex);
    } 
   } 
}