Damned MulticastSockets

aidan_walsh

Just doing some playing with MulticastSockets in Java for my own experience, but I'm damned if I can get them to work at all.

Every bit of documentation I can see about them says that all you have to do is create the object, join the group and send the data. Simple enough.

My problem is that though I'm following that, I can't seem to get it working.

InetAddress netAddress = InetAddress.getByName("239.255.255.250");
MulticastSocket mconn = new MulticastSocket(1900);
mconn.setTimeToLive(4);
mconn.joinGroup(netAddress);

String message = "stuff";
DatagramPacket datagram = new DatagramPacket(message.getBytes(), message.length());
mconn.send(datagram);

However, if I run that I'm getting a NullPointerException: null address || null buffer from the MulticastSocket.

Any ideas?

pH

Your current issue seems to be how you're creating the datagram packet:

Change this:

DatagramPacket datagram = new DatagramPacket(message.getBytes(), message.length());

to :

DatagramPacket datagram = new DatagramPacket(message.getBytes(), message.length(), netAddress, port);

aidan_walsh

D'oh, right you are. Cheers.