package cn.edu.buaa.multicast;

 import java.io.IOException;

 import java.net.DatagramPacket;

 import java.net.DatagramSocket;

 import java.net.InetAddress;

 import java.net.UnknownHostException;

 /**

  * One thing that we need to take into consideration here, is that there are

  * specific addresses that allow us to use a MulticastSocket are limited,

  * specifically in the range of 224.0.0.0 to 239.255.255.255. Some of them are

  * reserved, like 224.0.0.0. The address that we are using, 224.0.0.3, can be

  * used safely.

  */

 public class MulticastSocketServer {

     final static String INET_ADDR = "224.0.0.3";

     final static int PORT = 8888;

     public static void main(String[] args) throws UnknownHostException, InterruptedException {

         // Get the address that we are going to connect to.

         InetAddress addr = InetAddress.getByName(INET_ADDR);

         // Open a new DatagramSocket, which will be used to send the data.

         try (DatagramSocket serverSocket = new DatagramSocket()) {

             for (int i = 0; i < 5; i++) {

                 String msg = "Sent message no " + i;

                 // Create a packet that will contain the data

                 // (in the form of bytes) and send it.

                 DatagramPacket msgPacket = new DatagramPacket(msg.getBytes(), msg.getBytes().length, addr, PORT);

                 serverSocket.send(msgPacket);

                 System.out.println("Server sent packet with msg: " + msg);

                 Thread.sleep(500);

             }

         } catch (IOException ex) {

             ex.printStackTrace();

         }

     }

 }

 package cn.edu.buaa.multicast;

 import java.io.IOException;

 import java.net.DatagramPacket;

 import java.net.InetAddress;

 import java.net.MulticastSocket;

 import java.net.UnknownHostException;

 public class MulticastSocketClient {

     final static String INET_ADDR = "224.0.0.3";

     final static int PORT = 8888;

     public static void main(String[] args) throws UnknownHostException {

         // Get the address that we are going to connect to.

         InetAddress address = InetAddress.getByName(INET_ADDR);

         // Create a buffer of bytes, which will be used to store

         // the incoming bytes containing the information from the server.

         // Since the message is small here, 256 bytes should be enough.

         byte[] buf = new byte[256];

         // Create a new Multicast socket (that will allow other sockets/programs

         // to join it as well.

         try (MulticastSocket clientSocket = new MulticastSocket(PORT)) {

             // Joint the Multicast group.

             clientSocket.joinGroup(address);

             while (true) {

                 // Receive the information and print it.

                 DatagramPacket msgPacket = new DatagramPacket(buf, buf.length);

                 clientSocket.receive(msgPacket);

                 String msg = new String(buf, 0, buf.length);

                 System.out.println("Socket 1 received msg: " + msg);

             }

         } catch (IOException ex) {

             ex.printStackTrace();

         }

     }

 }