Java 多線程 Socket 聊天室：Server/Client 完整可運行代碼

架構概覽

• Server：主線程 ServerSocket.accept() 循環，每新連接啟動一個 ClientHandler 線程，廣播消息給所有在線客戶端。
• Client：兩線程——主線程讀取控制台輸入發送；ReaderThread 循環 socket.getInputStream().read() 打印接收消息。

Server 端

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

public class ChatServer {
    private static final int PORT = 8189;
    private static final List writers = Collections.synchronizedList(new ArrayList<>());

    public static void main(String[] args) throws IOException {
        System.out.println("Chat Server started on port " + PORT);
        try (ServerSocket listener = new ServerSocket(PORT)) {
            while (true) {
                new Handler(listener.accept()).start();
            }
        }
    }

    private static class Handler extends Thread {
        private Socket socket;
        private BufferedReader in;
        private PrintWriter out;

        public Handler(Socket socket) { this.socket = socket; }

        @Override public void run() {
            try {
                in = new BufferedReader(new InputStreamReader(socket.getInputStream(), "UTF-8"));
                out = new PrintWriter(new OutputStreamWriter(socket.getOutputStream(), "UTF-8"), true);
                writers.add(out);

                String msg;
                while ((msg = in.readLine()) != null) {
                    for (PrintWriter writer : writers) {
                        writer.println(msg);
                    }
                }
            } catch (IOException e) {
                System.out.println("Client error: " + e.getMessage());
            } finally {
                if (out != null) writers.remove(out);
                try { socket.close(); } catch (IOException ignored) {}
            }
        }
    }
}

Client 端

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

public class ChatClient {
    private static final String HOST = "localhost";
    private static final int PORT = 8189;

    public static void main(String[] args) throws IOException {
        try (Socket socket = new Socket(HOST, PORT);
             BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream(), "UTF-8"));
             PrintWriter out = new PrintWriter(new OutputStreamWriter(socket.getOutputStream(), "UTF-8"), true);
             Scanner scanner = new Scanner(System.in)) {

            System.out.print("請輸入暱稱: ");
            String nickname = scanner.nextLine();
            out.println("[" + nickname + "] 加入聊天室");

            // 接收線程
            new Thread(() -> {
                try {
                    String line;
                    while ((line = in.readLine()) != null) {
                        System.out.println(line);
                    }
                } catch (IOException ignored) {}
            }).start();

            // 發送循環
            String input;
            while (scanner.hasNextLine()) {
                input = scanner.nextLine();
                if ("/quit".equalsIgnoreCase(input)) break;
                out.println("[" + nickname + "] " + input);
            }
        }
    }
}

運行步驟

1. 編譯：javac ChatServer.java ChatClient.java
2. 啟動服務端：java ChatServer
3. 多終端啟動客戶端：java ChatClient

生產級擴展點

• 用 ExecutorService 替代顯式 new Thread，控制並發上限。
• 引入 Protocol（JSON/Protobuf）區分系統消息、私聊、群聊、心跳。
• Netty 重寫：事件驅動、零拷貝、SSL、WebSocket 支持。
• 持久化離線消息、用戶認證、房間管理。