1 package cn.edu.buaa.multicast; 2  3 import java.io.IOException; 4 import java.net.DatagramPacket; 5 import java.net.DatagramSocket; 6 import java.net.InetAddress; 7 import java.net.UnknownHostException; 8  9 /**10  * One thing that we need to take into consideration here, is that there are11  * specific addresses that allow us to use a MulticastSocket are limited,12  * specifically in the range of 224.0.0.0 to 239.255.255.255. Some of them are13  * reserved, like 224.0.0.0. The address that we are using, 224.0.0.3, can be14  * used safely.15  */16 public class MulticastSocketServer {17 18     final static String INET_ADDR = "224.0.0.3";19     final static int PORT = 8888;20 21     public static void main(String[] args) throws UnknownHostException, InterruptedException {22         // Get the address that we are going to connect to.23         InetAddress addr = InetAddress.getByName(INET_ADDR);24 25         // Open a new DatagramSocket, which will be used to send the data.26         try (DatagramSocket serverSocket = new DatagramSocket()) {27             for (int i = 0; i < 5; i++) {28                 String msg = "Sent message no " + i;29 30                 // Create a packet that will contain the data31                 // (in the form of bytes) and send it.32                 DatagramPacket msgPacket = new DatagramPacket(msg.getBytes(), msg.getBytes().length, addr, PORT);33                 serverSocket.send(msgPacket);34 35                 System.out.println("Server sent packet with msg: " + msg);36                 Thread.sleep(500);37             }38         } catch (IOException ex) {39             ex.printStackTrace();40         }41     }42 }

 1 package cn.edu.buaa.multicast; 2  3 import java.io.IOException; 4 import java.net.DatagramPacket; 5 import java.net.InetAddress; 6 import java.net.MulticastSocket; 7 import java.net.UnknownHostException; 8  9 public class MulticastSocketClient {10     final static String INET_ADDR = "224.0.0.3";11     final static int PORT = 8888;12 13     public static void main(String[] args) throws UnknownHostException {14         // Get the address that we are going to connect to.15         InetAddress address = InetAddress.getByName(INET_ADDR);16 17         // Create a buffer of bytes, which will be used to store18         // the incoming bytes containing the information from the server.19         // Since the message is small here, 256 bytes should be enough.20         byte[] buf = new byte[256];21 22         // Create a new Multicast socket (that will allow other sockets/programs23         // to join it as well.24         try (MulticastSocket clientSocket = new MulticastSocket(PORT)) {25             // Joint the Multicast group.26             clientSocket.joinGroup(address);27 28             while (true) {29                 // Receive the information and print it.30                 DatagramPacket msgPacket = new DatagramPacket(buf, buf.length);31                 clientSocket.receive(msgPacket);32 33                 String msg = new String(buf, 0, buf.length);34                 System.out.println("Socket 1 received msg: " + msg);35             }36         } catch (IOException ex) {37             ex.printStackTrace();38         }39     }40 }