运行客户端程序将创建一个客户端套接字，并与指定的服务器建立连接，接收了服务端发来的消息后关闭连接。服务端启动后会循环接收客户端连接，在接收到连接后，向该客户端发送 “Hello World!”.
实现在同一局域网下的一次简单的单向通信。
服务端Server.java：
package cs;import java.io.IOException;import java.io.OutputStream;import .InetAddress;import .ServerSocket;import .Socket;import java.nio.charset.StandardCharsets;public class Server {public void start(int port, int num, String ipAddress) {try {ServerSocket serverSocket = new ServerSocket(port, num, InetAddress.getByName(ipAddress));System.out.println("Server started on " + ipAddress + ":" + port);//服务端循环接收客户端连接，在接收到连接后，向该客户端发送"Hello World!"while (true) {Socket client = serverSocket.accept();System.out.println("Client " + client.getInetAddress() + " connected.");//向当前客户端发送消息OutputStream out = client.getOutputStream();out.write("Hello World!".getBytes(StandardCharsets.UTF_8));out.flush(); //作用是强制将缓冲区的数据输出到目的地,确保数据能够及时发送//进入死循环，保持连接不断开。持续监听当前客户端发送的消息，并在接收到消息时输出消息内容while (true) {//接收客户端发送的消息byte[] buf = new byte[1024];int len = client.getInputStream().read(buf);//若客户端断开连接if (len == -1) {System.out.println("Client " + client.getInetAddress() + " disconnected.");break;}//用于接收客户端发送的消息，注释掉是因为还未在客户端中写入发送消息的功能//else {// String str = new String(buf, 0, len, StandardCharsets.UTF_8);// System.out.println("Received message from client " + client.getInetAddress() + ": " + str);//}}}} catch (IOException e) {e.printStackTrace();}}public static void main(String[] args) {Server server = new Server();server.start(8888, 10, "192.168.202.31");//服务端在IP地址192.168.202.31 上启动，并设置端口号为8888//在ServerSocket这个函数中，第二个参数为backlog：指定连接请求队列的长度，如果连接请求队列已满，将拒绝新的连接请求。}}
客户端 Client.java：
package cs;import java.io.IOException;import java.io.InputStream;import .Socket;import java.nio.charset.StandardCharsets;public class Client {public void start(String serverIp, int serverPort) {try {Socket socket = new Socket(serverIp, serverPort);System.out.println("Connect to the server " + socket.getRemoteSocketAddress());//接收服务端发送的消息InputStream in = socket.getInputStream();byte[] buf = new byte[1024];int len = in.read(buf);String str = new String(buf, 0, len, StandardCharsets.UTF_8);System.out.println("Received message from the server: " + str);//关闭连接socket.close();} catch (IOException e) {e.printStackTrace();}}public static void main(String[] args) {Client client = new Client();client.start("192.168.202.31", 8888); //监听IP地址192.168.202.31 的8888端口}}
