import java.io.IOException;

import java.net.DatagramPacket;

import java.net.DatagramSocket;

import java.net.InetAddress;

public class server {

    public static void main(String[] args) throws IOException {

        DatagramSocket socket = new DatagramSocket(8080);

        byte[] data = new byte[1024];

        DatagramPacket packet = new DatagramPacket(data, data.length);

        socket.receive(packet);

        String info = new String(data, 0, packet.getLength());

        System.out.println("client：" + info);

        InetAddress address = packet.getAddress();

        int port = packet.getPort();

        byte[] data2 = "Hello Client!".getBytes();

        DatagramPacket packet2 = new DatagramPacket(data2, data2.length, address, port);

        socket.send(packet2);

        socket.close();

    }

}

import java.io.IOException;

import java.net.DatagramPacket;

import java.net.DatagramSocket;

import java.net.InetAddress;

public class client {

    public static void main(String[] args) throws IOException {

        InetAddress address = InetAddress.getByName("127.0.0.1");

        int port = 8080;

        byte[] data = "Hello Server!".getBytes();

        DatagramPacket packetSend = new DatagramPacket(data, data.length, address, port);

        DatagramSocket socket = new DatagramSocket(8888);

        socket.send(packetSend);

        byte[] dataRecv = new byte[1024];

        DatagramPacket packetRecv = new DatagramPacket(dataRecv, dataRecv.length);

        socket.receive(packetRecv);

        String reply = new String(dataRecv, 0, packetRecv.getLength());

        System.out.println("server：" + reply);

        socket.close();

    }

}