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Message:

here is the code

Posted by John Isner on February 13, 2002 at 9:53 AM

The code for both sender and the receiver is given below. After posting my question, I made an interesting (and confusing) discovery. If I use the multicast addresses 230.0.0.0 and 230.255.255.255, the receiver behaves correctly.

// -------------------- Sender -------------------------------------------------
import java.net.*;
import java.io.*;

public class Sender{
private static final int DESTINATION_PORT = 2101 /* 2101 */;
private DatagramSocket _socket;

public static void main(String args[]){
new Sender();
}
Sender(){
try{
_socket = new MulticastSocket();
}catch(IOException e){
System.out.println("could not create MulticastSocket");
System.exit(1);
}
InetAddress ballGroup = null;
try{
ballGroup = InetAddress.getByName("230.0.0.0");
}catch(UnknownHostException e){
System.out.println("could not create ballGroup");
System.exit(1);
}
InetAddress statusGroup = null;
try{
statusGroup = InetAddress.getByName("230.0.0.1");
}catch(UnknownHostException e){
System.out.println("could not create statusGroup");
System.exit(1);
}
while(true){
String message = null;
DatagramPacket packet = null;
byte data[] = null;

// send message "O75" to ball group

message = "O75";
data = message.getBytes();
packet = new DatagramPacket(data,data.length,ballGroup,DESTINATION_PORT);
try{
_socket.send(packet);
System.out.println("sent message " + message + " to ball group");
}catch(IOException e){
System.out.println("could not send packet to ballGroup");
System.exit(1);
}
try{
Thread.sleep(1000);
}catch(InterruptedException e){
System.exit(1);
}

// send message "playing" to status group

message = "playing";
data = message.getBytes();
packet = new DatagramPacket(data,data.length,statusGroup,DESTINATION_PORT);
try{
_socket.send(packet);
System.out.println("sent message " + message + " to status group");
}catch(IOException e){
System.out.println("could not send packet to statusGroup");
System.exit(1);
}
try{
Thread.sleep(4000);
}catch(InterruptedException e){
System.exit(1);
}
}
}
}
// ---------------------- Receiver -----------------------------------------
import java.net.*;
import java.io.*;
import java.util.*;

public class Receiver{
private static final int PORT = 2101;
public static void main(String args[]){
new Receiver();
}
private class BallListener implements Runnable{
public void run(){
MulticastSocket ballSocket = null;
try{
ballSocket = new MulticastSocket(PORT);
}catch(IOException e){
System.out.println("could not create ballSocket");
System.exit(1);
}
InetAddress ballGroup = null;
try{
ballGroup = InetAddress.getByName("230.0.0.0");
}catch(UnknownHostException e){
System.out.println("could not create ballGroup");
System.exit(1);
}
try{
ballSocket.joinGroup(ballGroup);
}catch(IOException e){
System.out.println("ballSocket.joinGroup(ballGroup) failed");
System.exit(1);
}
while(true){
byte buf[] = new byte[256];
DatagramPacket packet = new DatagramPacket(buf,256);
try {
ballSocket.receive(packet);
}catch(IOException e) {
System.out.println("ballSocket.receive() failed");
e.printStackTrace();
System.exit(1);
}
byte data[] = packet.getData();
String temp = new String(data);
String message = temp.trim();
System.err.println("BallListener received " + message);
}
}
}
private class StatusListener implements Runnable{
public synchronized void run(){
MulticastSocket statusSocket = null;
try{
statusSocket = new MulticastSocket(PORT);
}catch(IOException e){
System.out.println("could not create statusSocket");
System.exit(1);
}
InetAddress statusGroup = null;
try{
statusGroup = InetAddress.getByName("230.0.0.1");
}catch(UnknownHostException e){
System.out.println("could not create statusGroup");
System.exit(1);
}
try{
statusSocket.joinGroup(statusGroup);
}catch(IOException e){
System.out.println("statusSocket.joinGroup(statusGroup) failed");
e.printStackTrace();
System.exit(1);
}
while(true){
byte buf[] = new byte[256];
DatagramPacket packet = new DatagramPacket(buf,256);
try {
statusSocket.receive(packet);
}catch(IOException e) {
System.out.println("statusSocket.receive() failed");
e.printStackTrace();
System.exit(1);
}
byte data[] = packet.getData();
String temp = new String(data);
String message = temp.trim();
System.err.println("StatusListener received " + message);
}
}
}
Receiver(){
new Thread(new StatusListener()).start();
new Thread(new BallListener()).start();
}
}

> if you could post the sending part, I mean the actual code,
> something like the following:

> InetAddress group = InetAddress.getByName("228.5.6.7");
> MulticastSocket s = new MulticastSocket(port);
> DatagramPacket packet = new DatagramPacket(msg.getBytes(),msg.length(), group, port);
> s.send(packet );

> will be helpful to determine what goes wrong
>