最简单的UDP程序

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.util.Scanner;

public class SendDemo {
    public static void main(String[] args) throws IOException {
        while (true) {
            System.out.print("Please input data:");
            byte[] say = new Scanner(System.in).nextLine().getBytes();
            DatagramSocket ds = new DatagramSocket();
            DatagramPacket dp = new DatagramPacket(say, say.length,
                    InetAddress.getByName("127.0.0.1"), 1357);
            ds.send(dp);
        }
    }
}

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;

public class ReceiveDemo {
    public static void main(String[] args) throws IOException {
        DatagramSocket ds = new DatagramSocket(1357);
        while (true) {
            byte[] buf = new byte[2048];
            DatagramPacket dp = new DatagramPacket(buf, buf.length);
            ds.receive(dp);
            System.out.println("from:" + dp.getAddress().getHostName()
                    + " message:"
                    + new String(dp.getData(), 0, dp.getData().length));
        }
    }
}