Java 实现UDP打洞,该如何处理

//服务器端import java.io.IOException;import java.net.DatagramPacket;import java.net.DatagramSocket;public class TestServer {    public static void main(String[] args) throws IOException     {        DatagramSocket chatUDPSocket = new DatagramSocket(8888);        while(true)        {            byte[] recvBuf = new byte[100];            DatagramPacket recvPacket = new DatagramPacket(recvBuf , recvBuf.length);            chatUDPSocket.receive(recvPacket);            System.out.println(recvPacket.getSocketAddress().toString());        }    }}

import java.io.IOException;import java.net.DatagramPacket;import java.net.DatagramSocket;import java.net.InetAddress;import java.util.Scanner;public class TestClient {    public static void main(String[] args) throws IOException     {        DatagramSocket clienttoclient = new DatagramSocket();        String sendStr = "hello";        byte[] sendBuf = sendStr.getBytes();        InetAddress addr = InetAddress.getByName("125.34.69.243");        int port = 8888;        DatagramPacket sendPacket             = new DatagramPacket(sendBuf ,sendBuf.length , addr , port);        clienttoclient.send(sendPacket);                new ReceiveMessages(clienttoclient);                System.out.println("输入要联系的IP地址");        Scanner in = new Scanner(System.in);        String userIP = in.next();        System.out.println("输入要联系的端口号");        int userPort = in.nextInt();                byte[] chatsendBuf = "hello".getBytes();        InetAddress chatAddr = InetAddress.getByName(userIP);        DatagramPacket chatsendPacket = new DatagramPacket(chatsendBuf,chatsendBuf.length,chatAddr,userPort);        clienttoclient.send(chatsendPacket);        System.out.println("test");    }}class ReceiveMessages extends Thread{    private DatagramSocket clienttoclient;    public ReceiveMessages(DatagramSocket clienttoclient)    {        this.clienttoclient = clienttoclient;        this.start();    }    public void run()    {        System.out.println("启动监听客户端接收客户端发送的消息");        byte[] recvBuf = new byte[100];        DatagramPacket recvPacket            = new DatagramPacket(recvBuf , recvBuf.length);        try {            clienttoclient.receive(recvPacket);        } catch (IOException e) {            e.printStackTrace();        }        String recvStr = new String(recvPacket.getData() , 0 ,recvPacket.getLength());        System.out.println("收到:" + recvStr);    }}