网络编程也有趣的，Java中有对系统网络IO操作的封装包：Socket。现在我们在本地电脑（网络）用它来模拟一个简单的群聊功能，以便能更好地对网络编程进行深刻的理解。

"Client"去连接"Host",可同时多有多个"Client"去连接"Host"；

在IDEA中，要多开一个程序(重复运行一个程序)，可能需要关闭配置的"single instance only"，或者打开"Allow parallel run"。

即可实现应用多开（并行运行）。

这是一个服务主机端的模拟代码：

/**
 * @ Annotation:模拟服务器，实现群聊(群发)
 */
public class Host {
    public static void main(String[] args) {
        try {
            System.out.println("Host start");
            List<Socket> onlineSocket = new ArrayList<>();
            //assign port:8898
            ServerSocket server = new ServerSocket(8898);
            while (true) {
                Socket socket = server.accept();//monitor port:8898
                System.out.println("a client:" + socket.getRemoteSocketAddress() + " online");
                new Thread(() -> {
                    System.out.println("current thread id of host for new client is:" + Thread.currentThread().getId());
                    try {
                        InputStream is = socket.getInputStream();
                        DataInputStream dis = new DataInputStream(is);
                        while (true) {
                            try {
                                String content = dis.readUTF(dis);
                                System.out.println(content);
                                //static content
                                for (Socket oc : onlineSocket) {
                                    OutputStream os = oc.getOutputStream();
                                    DataOutputStream dos = new DataOutputStream(os);
                                    dos.writeUTF(content);
                                    dos.flush();
                                }
                            } catch (Exception e) {
                                System.out.println("a client:" + socket.getRemoteSocketAddress() + "offline");
                                onlineSocket.remove(socket);
                                dis.close();
                                socket.close();
                                break;
                            }

                        }
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }).start();
                onlineSocket.add(socket);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

这是一个客户端的模拟代码： 

/**
 * @ Author Jam·Li
 * @ Date 2024/9/8 19:13
 * @ version 1.0.0
 * @ Annotation:模拟客户端，可多开
 */
public class Client {
    public static void main(String[] args) {
        try {
            //Socket client = new Socket(InetAddress.getLocalHost(), 8898);
            Socket client = new Socket("127.0.0.1", 8898);
            new Thread(()->{
                try {
                    InputStream is = client.getInputStream();
                    DataInputStream dis = new DataInputStream(is);
                    while (true){
                        try {
                            String msg = dis.readUTF(dis);
                            System.out.println(msg);
                        } catch (Exception e) {
                            dis.close();
                            client.close();
                            System.out.println("I offline: "+client.getRemoteSocketAddress()+" now.");
                            break;
                        }
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }).start();
            OutputStream os = client.getOutputStream();
            DataOutputStream dos = new DataOutputStream(os);
            Scanner scanner = new Scanner(System.in);
            while (true){
                System.out.println("Input Content Please");
                String msg = scanner.nextLine();
                dos.writeUTF(msg);
                dos.flush();
                System.out.println("Sent.");
                if (msg.equals("Bye")){
                    client.close();
                    dos.close();
                    System.out.println("See you~");
                    break;
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

 先打开服务主机端：

再打开客户端：

 

多开客户端： 

 

 

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