//需求2：客户端发送信息给服务端，服务端接收信息，然后服务端发送信息回给客户端 //需求3：循环执行客户端和服务端交流【Scanner】

这是一个简单的客户端-服务端通信的代码示例，需要使用 Java 的 Socket 编程实现：

服务端代码：

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

public class Server {
    public static void main(String[] args) {
        try {
            ServerSocket serverSocket = new ServerSocket(8888);
            System.out.println("Server started.");
            Socket socket = serverSocket.accept();
            System.out.println("Client connected.");

            BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            PrintWriter out = new PrintWriter(socket.getOutputStream(), true);

            String inputLine;
            while ((inputLine = in.readLine()) != null) {
                System.out.println("Client: " + inputLine);
                out.println("Server: " + inputLine);
            }

            socket.close();
            serverSocket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

客户端代码：

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

public class Client {
    public static void main(String[] args) {
        try {
            Socket socket = new Socket("localhost", 8888);
            System.out.println("Connected to server.");

            BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            PrintWriter out = new PrintWriter(socket.getOutputStream(), true);

            Scanner scanner = new Scanner(System.in);
            String inputLine;
            while (true) {
                System.out.print("Client: ");
                inputLine = scanner.nextLine();
                out.println(inputLine);
                System.out.println("Server: " + in.readLine());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

这里使用了 Scanner 来循环执行客户端和服务端的交流。