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

/**
 * @author 興趣使然黃小黃
 * @version 1.0
 * 接收端A
 */
public class UDPReceiverA {
    public static void main(String[] args) throws IOException {
        //1.創(chuàng)建一個(gè)DatagramSocket對(duì)象，準(zhǔn)備在9999接收數(shù)據(jù)
        DatagramSocket socket = new DatagramSocket(9999);
        //2.構(gòu)建一個(gè)DatagramPacket對(duì)象，準(zhǔn)備接收數(shù)據(jù)
        byte[] buf = new byte[1024];
        DatagramPacket packet = new DatagramPacket(buf, buf.length);
        //3.調(diào)用接收方法,將通過網(wǎng)絡(luò)傳輸?shù)?DatagramPacket對(duì)象 填充到 packet對(duì)象
        System.out.println("接收端A 等待接收數(shù)據(jù)...");
        socket.receive(packet);
        //4.把packet進(jìn)行拆包，取出數(shù)據(jù)
        int length = packet.getLength();//實(shí)際數(shù)據(jù)字節(jié)長(zhǎng)度
        byte[] data = packet.getData();//實(shí)際接收的數(shù)據(jù)
        String s = new String(data, 0, length);
        System.out.println(s);

        //回復(fù)信息給B端
        data = "你好！發(fā)送端".getBytes();
        packet = new DatagramPacket(data, 0, data.length,
                InetAddress.getLocalHost(), 9998);
        socket.send(packet);
        //5.關(guān)閉資源
        socket.close();
    }
}

import java.io.IOException;
import java.net.*;

/**
 * @author 興趣使然黃小黃
 * @version 1.0
 * 發(fā)送端B
 */
public class UDPSenderB {
    public static void main(String[] args) throws IOException {
        //1.創(chuàng)建 DatagramSocket 對(duì)象，準(zhǔn)備在9998發(fā)送和接收數(shù)據(jù)
        DatagramSocket socket = new DatagramSocket(9998);
        //2.將需要發(fā)送的數(shù)據(jù)，封裝到 DatagramPacket 中
        byte[] data = "你好！接收端".getBytes();
        DatagramPacket datagramPacket =
                new DatagramPacket(data, 0, data.length,
                        InetAddress.getLocalHost(), 9999);
        socket.send(datagramPacket);

        //接收A消息
        socket.receive(datagramPacket);
        int length = datagramPacket.getLength();//實(shí)際數(shù)據(jù)字節(jié)長(zhǎng)度
        data = datagramPacket.getData();//實(shí)際接收的數(shù)據(jù)
        String s = new String(data, 0, length);
        System.out.println(s);
        //關(guān)閉資源
        socket.close();
    }
}