266. Writing a UDP multicast server/client application

In Problem 263, we developed a UDP server/client application. So, based on that experience, we can go further and highlight the main aspects that can transform a classical UDP-based application into a multicast one.

For instance, let’s assume that we want to write a multicast server that sends to the group (to all members interested in receiving datagrams from this server) a datagram that encapsulates the current date-time on the server. This datagram is sent every 10 seconds.

Writing a UDP multicast server

Writing a UDP multicast server starts with a new DatagramChannel instance obtained via the open() method. Next, we set the IP_MULTICAST_IF option (used to indicate the multicast network interface) and the SO_REUSEADDR option (used to allow multiple members to bind to the same address – this should be done before binding the socket):

private static final String 
  MULTICAST_NI_NAME = "ethernet_32775...