udp chatting with multiple client and a server

hi,
I need the code for udp chatting using multicasting with multiple clients and a server.
If clients type and send messages to server,then it should be displayed in server.
If server type and send message, then it should be displayed in all the clients.

I need the code in java. The chatting is done in console i.e., command prompt. not in GUI.

plz help