9.UDP

发短信：不用连接，需要知道对方的地址！就像发射导弹，我需要知道轰炸地点，但不需要告诉对方，秘密轰炸，嘿嘿。

需要了解DatagramPacket，DatagramSocket两个类

发送端：

package com.Inet.lesson3;

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

//不需要连接服务器
public class UdpClientDemo01 {
    public static void main(String[] args) throws Exception {
        //1.建立一个Socket
        DatagramSocket socket = new DatagramSocket();

        //2.建个包
        String msg = "你好啊，服务器";

        //发送给谁
        InetAddress localhost = InetAddress.getByName("localhost");
        int port = 9090;
        DatagramPacket packet = new DatagramPacket(msg.getBytes(), 0, msg.getBytes().length, localhost, port);

        //3.发送包
        socket.send(packet);

        //4.关闭流
        socket.close();
    }
}

接收端

package com.Inet.lesson3;

import java.net.DatagramPacket;
import java.net.DatagramSocket;

//还是要等待客户端的链接！
public class UdpServerDemo01 {
    public static void main(String[] args) throws Exception {
        //开放端口
        DatagramSocket socket = new DatagramSocket(9090);

        //接收数据包
        byte[] buffer = new byte[1024];
        DatagramPacket packet = new DatagramPacket(buffer, 0, buffer.length);//接收

        socket.receive(packet);//阻塞接收

        System.out.println(packet.getAddress().getHostAddress());
        System.out.println(new String(packet.getData(), 0, packet.getLength()));

        //关闭连接
        socket.close();
    }
}

//先启动接收端，再启动发送端
结果：
127.0.0.1
你好啊，服务器