Salut ^^

Envoie d'un paquet en UDP :

InetAddress address = InetAddress.getByName("hostName");
int port = 4321;

String ch = "Le message à envoyer";
int chl = ch.length;

byte[] message = new byte[chl];
ch.getBytes(0, chl, message, 0);

DatagramPacket p = new DatagramPacket(message, chl, address, port);
datagramSocket s = new DatagramSocket();

s.send(p);

Reception du paquet :

byte[] buffer = new byte[1024];
String ch;

DatagramPacket p = new DatagramPacket(buffer, buffer.length);
datagramSocket s = new DatagramSocket(4321);

while(true) {
s.receive(p);
ch = new String(buffer, 0, 0, p.getLength());

System.out.println("Paquet recu : message = " + ch +
" - envoyeur = " +
p.getAddress.getHostName() +
" - port = " + p.getPort());
}