IP Multicast - Java Network Programming - page 457

Leaving groups and closing the connection
Call the leaveGroup() method when you no longer want to receive datagrams from the
specified multicast group, on either all or a specified network interface:
public void leaveGroup ( InetAddress address ) throws IOException
public void leaveGroup ( SocketAddress multicastAddress ,
NetworkInterface interface )
throws IOException
It signals the local multicast router, telling it to stop sending you datagrams. If the
address you try to leave is not a multicast address (if it is not between 224.0.0.0 and
239.255.255.255), the method throws an IOException . However, no exception occurs
if you leave a multicast group you never joined.
Pretty much all the methods in MulticastSocket can throw an IOException , so you'll
usually wrap all this in a try block. In Java 7, DatagramSocket implements
Autocloseable so you can use try-with-resources:
try ( MulticastSocket socket = new MulticastSocket ()) {
// connect to the server...
} catch ( IOException ex ) {
ex . printStackTrace ();
}
In Java 6 and earlier, you'll want to explicitly close the socket in a finally block to
release resources the socket holds:
MulticastSocket socket = null ;
try {
socket = new MulticastSocket ();
// connect to the server...
} catch ( IOException ex ) {
ex . printStackTrace ();
} finally {
if ( socket != null ) {
try {
socket . close ();
} catch ( IOException ex ) {
// ignore
}
}
}
Sending multicast data
Sending data with a MulticastSocket is similar to sending data with a DatagramSock
et . Stuff your data into a DatagramPacket object and send it off using the send() method
inherited from DatagramSocket . The data is sent to every host that belongs to the mul‐
ticast group to which the packet is addressed. For example: