编写 UDP版本的 echo server 和 echo client

代码如下

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;
// UDP 的 回显服务器.
public class UdpEchoServer {
    private DatagramSocket socket = null;

    //参数是服务器要绑定的窗口
    public UdpEchoServer(int port) throws SocketException {
        socket = new DatagramSocket(port);
    }

    //使用这个方法启动服务器
    public void start() throws IOException {
        System.out.println("服务器启动!");
        while (true) {
            //反复长期执行针对客户端请求处理的逻辑
            //一个服务器,运行过程中要做的事情主要三个环节
            //1.读取 请求,并解析
            DatagramPacket requestPacket = new DatagramPacket(new byte[4096],4096);
            socket.receive(requestPacket);
            //这样转字符串的前提是,后续客户端发的数据就是一个文本的字符串
            String request = new String(requestPacket.getData(),0, requestPacket.getLength());
            //根据请求,做出响应
            String response = process(request);
            //3.把响应写回客户端
            //此时需告知网卡,要发的内容是啥,要发给谁
            DatagramPacket responsePacket = new DatagramPacket(request.getBytes(), request.getBytes().length,
                    requestPacket.getSocketAddress());
            socket.send(requestPacket);
            //记录日志,方便观察程序执行结果
            System.out.printf("[%s:%d] req: %s, resp: %s\n", requestPacket.getAddress().toString(), requestPacket.getPort(),
                    request, response);;
        }
    }

    //根据请求计算响应,由于是回显程序,响应内容和请求完全一样
    private String process(String request) {
        return request;
    }

    public static void main(String[] args) throws IOException {
        UdpEchoServer server = new UdpEchoServer(9090);
        server.start();
    }
}

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

public class UdpEchoClient {
    private DatagramSocket socket = null;
    private String serverIp;
    private int serverPort;

    //服务器的IP和服务器的端口
    public UdpEchoClient(String ip,int port) throws SocketException {
        serverIp = ip;
        serverPort = port;
        //这个new操作,就不再指定端口了,让系统自动分配一个空闲端口
        socket = new DatagramSocket();
    }

    //让客户端反复的从控制台读取用户输入的内容,把这个内容构造成UDP请求,发给服务器,再读取服务器返回的UDP响应
    //最终显示在用户的屏幕上
    public void start() throws IOException {
        Scanner scanner = new Scanner(System.in);
        System.out.println("客户端启动!");
        while (true) {
            //1.从控制台读取用户输入的内容
            System.out.print("->");
            String request = scanner.next();
            //2.构造请求对象,并发给服务器
            DatagramPacket requestPacket = new DatagramPacket(request.getBytes(),request.getBytes().length,
                    InetAddress.getByName(serverIp),serverPort);
            socket.send(requestPacket);
            //3.读取服务器的响应,并解析出响应内容
            DatagramPacket responsPacket = new DatagramPacket(new byte[4096],4096);
            socket.receive(responsPacket);
            String response = new String(responsPacket.getData(), responsPacket.getData().length);
            //4.显示到屏幕上
            System.out.println(response);
        }
    }

    public static void main(String[] args) throws IOException {
        UdpEchoClient client = new UdpEchoClient("127.0.0.1",9090);
        client.start();
    }
}