傳送方：Demo002Send.java

package com.shsxt.day09.udp;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.InetSocketAddress;

/*
 * 傳送方：
 * 1、準備一個數據報  傳送工具   DatagramSocket
 * 2、準備資料
 * 3、準備資料報包     （資料+ 地址（ip+埠號））
 * 4、傳送 （使用資料報傳送出資料報包）
 * 5、釋放資源
 */
 

public class Demo002Send {
    public static void main(String[] args)throws Exception {

        DatagramSocket socket = new DatagramSocket(2626);

        //byte[] msg = "hello".getBytes();
        // 輸入資料傳送
        /*Scanner sc = new Scanner(System.in);
        String m = sc.nextLine();
        byte[] msg = m.getBytes();*/
 

        // System.in   -> 標準輸入流
        BufferedReader bis = new BufferedReader(new InputStreamReader(System.in));
        byte[] msg = bis.readLine().getBytes();


        InetAddress address = InetAddress.getByName("127.0.0.1");
        InetSocketAddress socketAddress = new InetSocketAddress(address, 3535
 
);

        DatagramPacket p = new DatagramPacket(msg, msg.length,socketAddress);

        socket.send(p);
        socket.close();


        DatagramSocket socket1 = new DatagramSocket(5454);
        byte[] ms = new byte[1024];
        DatagramPacket dp = new DatagramPacket(ms,ms.length);
        socket1.receive(dp);
        int len = dp.getLength();
        System.out.println(new String(ms,0,len));

        socket1.close();


    }
}

接收方：Demo002Receive

package com.shsxt.day09.udp;

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.InetSocketAddress;

/*
 * 1、準備一個數據報  接收資料的工具    指定自己在哪個埠接收
 * 2、準備接收資料的容器 
 * 3、準備一個空的資料報包
 * 4、接收
 * 5、釋放資源
 */
public class Demo002Receive {
    public static void main(String[] args) throws Exception {
        DatagramSocket socket = new DatagramSocket(3535);

        byte[] msg = new byte[1024];
        DatagramPacket packet = new DatagramPacket(msg,msg.length);
        //    阻塞在此等待資料
        socket.receive(packet);

        int len = packet.getLength();

        String str = new String(msg,0,len);
        System.out.println(str);


        // 獲取傳送方資訊， 準備回覆資訊
        InetAddress address = packet.getAddress();
        InetSocketAddress socketAddress = new InetSocketAddress(address, 5454);

        String ms = "來自對方回覆：" + str;

        DatagramPacket dp = new DatagramPacket(ms.getBytes(),ms.getBytes().length,socketAddress);
        socket.send(dp);

        socket.close();



    }
}