java怎么编写简单聊天室

要用Java编写一个简单的聊天室，你可以使用套接字编程（Socket Programming）。这里是一个基本的聊天室实现教程：

1. 创建服务器端（Server）代码：

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

public class ChatServer {
    private static final int PORT = 12345;
    private static Socket socket;

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

        while (true) {
            socket = serverSocket.accept();
            System.out.println("客户端已连接：" + socket.getInetAddress());

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

            String userInput;
            while ((userInput = in.readLine()) != null) {
                System.out.println("收到消息：" + userInput);
                broadcastMessage(out, userInput);
            }

            socket.close();
        }
    }

    private static void broadcastMessage(PrintWriter out, String message) {
        for (Socket client : new ArrayList(clients)) {
            if (client != socket) {
                try {
                    out.println(message);
                } catch (IOException e) {
                    e.printStackTrace();
                    clients.remove(client);
                    try {
                        client.close();
                    } catch (IOException e1) {
                        e1.printStackTrace();
                    }
                }
            }
        }
    }
}

2. 创建客户端（Client）代码：

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

public class ChatClient {
    private static final String SERVER_ADDRESS = "localhost";
    private static final int PORT = 12345;
    private static Socket socket;
    private static BufferedReader in;
    private static PrintWriter out;

    public static void main(String[] args) throws IOException {
        socket = new Socket(SERVER_ADDRESS, PORT);
        System.out.println("已连接到服务器：" + SERVER_ADDRESS + ":" + PORT);

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

        BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
        String userInput;

        while (true) {
            System.out.print("请输入消息：");
            userInput = stdIn.readLine();
            if (userInput.equalsIgnoreCase("exit")) {
                break;
            }
            out.println(userInput);
            System.out.println("服务器回复：" + in.readLine());
        }

        socket.close();
    }
}

3. 分别运行服务器端和客户端代码。首先启动服务器端，然后启动一个或多个客户端。现在可以在客户端输入消息并查看服务器的回复。

注意：这个示例仅适用于单个服务器和客户端。要实现多个客户端之间的通信，可以将客户端添加到clients列表中，并在broadcastMessage方法中遍历该列表以向所有客户端发送消息。同时，为了简化代码，这里没有处理异常。在实际应用中，应该对异常进行适当的处理。