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:8898ServerSocket server = new ServerSocket(8898);while (true) {Socket socket = server.accept();//monitor port:8898System.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 contentfor (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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