udp 传输，可解决中文不能正确传输，乱码问题

// join a Multicast group and send the group salutations
...
String msg = "Hello";
InetAddress group = InetAddress.getByName("228.5.6.7");
MulticastSocket s = new MulticastSocket(6789);
s.joinGroup(group);
DatagramPacket hi = new DatagramPacket(msg.getBytes(), msg.length(),
group, 6789);
s.send(hi);
// get their responses!
byte[] buf = new byte[1000];
DatagramPacket recv = new DatagramPacket(buf, buf.length);
s.receive(recv);
...
// OK, I'm done talking - leave the group...
s.leaveGroup(group);

public class MudpSrv {

int port = 6789;

public void sendMessage(String msg,MulticastSocket socket) throws IOException{
ByteArrayOutputStream ostream = new ByteArrayOutputStream();
DataOutputStream dataStream = new DataOutputStream(ostream);
dataStream.writeUTF(msg);
dataStream.close();

byte[] data = ostream.toByteArray();

InetAddress address = InetAddress.getByName("230.3.3.3");
socket.joinGroup(address);
DatagramPacket dp = new DatagramPacket(data, data.length, address,port);
socket.send(dp);
}

public void getMessage(MulticastSocket socket) throws IOException{
byte[] bs = new byte[1000];
DatagramPacket packet = new DatagramPacket(bs, bs.length);
socket.receive(packet);

DataInputStream istream = new DataInputStream(new ByteArrayInputStream(packet.getData(), packet.getOffset(), packet.getLength()));

String msg = istream.readUTF();

System.out.println(msg);
}

public static void main(String args[]) throws IOException{
MudpSrv srv = new MudpSrv();
MulticastSocket socket = new MulticastSocket(srv.port);
srv.sendMessage("萤火虫，皎白月光，游过四季",socket);
srv.getMessage(socket);
}

}