【从零学javase 第六天】网络编程（+多线程）

Java 网络编程实战教程：从零基础到群聊

本文适合刚会 Java 的同学，带你从零基础学 Java 网络编程，最终实现多客户端群聊。

一、网络编程基础概念

网络编程就是用程序让两台电脑互相传递信息。

IP 地址 ：电脑的网络位置，例如 127.0.0.1（本机）
端口号 ：程序监听的"门牌号"，例如 8888
客户端（Client）：发送消息
服务器（Server）：接收消息

TCP（可靠通信）与 UDP（快速通信）：

TCP：保证顺序、保证不丢包，适合聊天、文件传输
UDP：不保证顺序、可能丢包，适合视频、语音、游戏

本文先用 TCP 实现基础聊天程序，然后扩展到多客户端和群聊。

二、单客户端聊天（客户端 + 服务器）

服务器端（Server.java）

java 复制代码

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

public class Server {
    public static void main(String[] args) throws Exception {
        ServerSocket server = new ServerSocket(8888);
        System.out.println("服务器启动，等待客户端连接...");

        Socket socket = server.accept();
        System.out.println("客户端已连接");

        BufferedReader reader = new BufferedReader(
            new InputStreamReader(socket.getInputStream()));
        PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);

        String msg;
        while ((msg = reader.readLine()) != null) {
            System.out.println("客户端说：" + msg);
            writer.println("收到：" + msg);
            if (msg.equalsIgnoreCase("bye")) break;
        }

        socket.close();
        server.close();
    }
}

客户端（Client.java)

java 复制代码

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

public class Client {
    public static void main(String[] args) throws Exception {
        Socket socket = new Socket("127.0.0.1", 8888);
        System.out.println("已连接服务器");

        BufferedReader console = new BufferedReader(new InputStreamReader(System.in));
        BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);

        String msg;
        while (true) {
            System.out.print("发送给服务器：");
            msg = console.readLine();
            writer.println(msg);
            if (msg.equalsIgnoreCase("bye")) break;
            String reply = reader.readLine();
            System.out.println("服务器说：" + reply);
        }

        socket.close();
    }
}

三、多线程服务器（同时服务多个客户端）

java 复制代码

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

public class MultiServer {
    public static void main(String[] args) throws Exception {
        ServerSocket server = new ServerSocket(8888);
        System.out.println("多线程服务器启动...");

        while (true) {
            Socket socket = server.accept();
            new Thread(() -> handleClient(socket)).start();
        }
    }

    private static void handleClient(Socket socket) {
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);

            String msg;
            while ((msg = reader.readLine()) != null) {
                System.out.println("客户端说：" + msg);
                writer.println("收到：" + msg);
                if (msg.equalsIgnoreCase("bye")) break;
            }

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

四、群聊功能实现

java 复制代码

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

public class ChatServer {
    private static List<PrintWriter> clients = new ArrayList<>();

    public static void main(String[] args) throws Exception {
        ServerSocket server = new ServerSocket(8888);
        System.out.println("群聊服务器启动...");

        while (true) {
            Socket socket = server.accept();
            new Thread(() -> handleClient(socket)).start();
        }
    }

    private static void handleClient(Socket socket) {
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);

            synchronized (clients) { clients.add(writer); }

            String msg;
            while ((msg = reader.readLine()) != null) {
                System.out.println("收到：" + msg);
                broadcast(msg);
                if (msg.equalsIgnoreCase("bye")) break;
            }

            synchronized (clients) { clients.remove(writer); }
            socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static void broadcast(String msg) {
        synchronized (clients) {
            for (PrintWriter out : clients) {
                out.println(msg);
            }
        }
    }
}