In this post, a group chat application using MulticastSocket (Java Platform SE 7) class is discussed. A MulticastSocket is a (UDP) DatagramSocket, with additional capabilities for joining “groups” of other multicast hosts on the internet.
import java.net.*;
import java.io.*;
import java.util.*;
public class GroupChat
{
private static final String TERMINATE = "Exit";
static String name;
static volatile boolean finished = false;
public static void main(String[] args)
{
if (args.length != 2)
System.out.println("Two arguments required: <multicast-host> <port-number>");
else
{
try
{
InetAddress group = InetAddress.getByName(args[0]);
int port = Integer.parseInt(args[1]);
Scanner sc = new Scanner(System.in);
System.out.print("Enter your name: ");
name = sc.nextLine();
MulticastSocket socket = new MulticastSocket(port);
// Since we are deploying
socket.setTimeToLive(0);
//this on localhost only (For a subnet set it as 1)
socket.joinGroup(group);
Thread t = new Thread(new
ReadThread(socket,group,port));
// Spawn a thread for reading messages
t.start();
// sent to the current group
System.out.println("Start typing messages...\n");
while(true)
{
String message;
message = sc.nextLine();
if(message.equalsIgnoreCase(GroupChat.TERMINATE))
{
finished = true;
socket.leaveGroup(group);
socket.close();
break;
}
message = name + ": " + message;
byte[] buffer = message.getBytes();
DatagramPacket datagram = new
DatagramPacket(buffer,buffer.length,group,port);
socket.send(datagram);
}
}
catch(SocketException se)
{
System.out.println("Error creating socket");
se.printStackTrace();
}
catch(IOException ie)
{
System.out.println("Error reading/writing from/to socket");
ie.printStackTrace();
}
}
}
}
class ReadThread implements Runnable
{
private MulticastSocket socket;
private InetAddress group;
private int port;
private static final int MAX_LEN = 1000;
ReadThread(MulticastSocket socket,InetAddress group,int port)
{
this.socket = socket;
this.group = group;
this.port = port;
}
@Override
public void run()
{
while(!GroupChat.finished)
{
byte[] buffer = new byte[ReadThread.MAX_LEN];
DatagramPacket datagram = new
DatagramPacket(buffer,buffer.length,group,port);
String message;
try
{
socket.receive(datagram);
message = new
String(buffer,0,datagram.getLength(),"UTF-8");
if(!message.startsWith(GroupChat.name))
System.out.println(message);
}
catch(IOException e)
{
System.out.println("Socket closed!");
}
}
}
}