签到2：
签到界面上有时间显示，签到码输入框，开始签到，当倒计时结束，老师端和学生端都会显示签到结果，所以签到结果需要建表：（签到了的学生和未签到的学生，
这次签到的时间和签到码，班级号，）
签到有已签到，未签到
判断是否签的是以前的到就是看有没有结束时间

随机选人:
两遍遍历数据库，第一遍从数据库里把班级里所有学生挑出来，并定义一个变量每挑一个记录变量加1，然后使用redom随机数随机1-n这个范围内的数
第二遍再定义一个变量然后再遍历一遍直到数字等于随机数，然后把名字随机出来

if(receive.equals("Release success")){Alert alert = new Alert(Alert.AlertType.INFORMATION);alert.setTitle("Information Dialog");alert.setHeaderText(null);alert.setContentText("发布签到成功");// 显示提醒框并等待用户关闭alert.showAndWait();initializeTableView_second();tabpane.getSelectionModel().select(Check_in);Socket socket3 = new Socket("127.0.0.1", 10090);String judgment3 = "update_check_in";ObjectOutputStream oos3 = new ObjectOutputStream(socket3.getOutputStream());oos3.writeObject(judgment3);      //传送标志oos3.writeObject(formattedTime);ObjectInputStream ois3 = new ObjectInputStream(socket3.getInputStream());Object obj = ois3.readObject();if (studentsList != null && !studentsList.isEmpty()) {studentsList.clear();}if (obj instanceof ArrayList<?>) {studentsList = (ArrayList<String>) obj;}Map<String, String> studentStatusMap = new HashMap<>();for (String student : studentsList) {studentStatusMap.put(student, "未签到");}socket4 = new Socket("127.0.0.1", 10090);judgment4 = "update_examine_check_in";oos4 = new ObjectOutputStream(socket4.getOutputStream());oos4.writeObject(judgment4);Thread countdownThread = new Thread(() -> {int totalSeconds = Integer.parseInt(minute) * 60 + Integer.parseInt(second_clock);while (totalSeconds > 0) {try {// 将 totalSeconds 转换为分钟和秒钟int minutes = totalSeconds / 60;int seconds = totalSeconds % 60;// 更新界面上的显示（这里使用 Platform.runLater 来在 JavaFX 应用程序线程中更新 UI）Platform.runLater(() -> {minutetext.setText(String.valueOf(minutes));second_clocktext.setText(String.valueOf(seconds));});for (String student : studentsList) {oos4.writeObject(student);oos4.writeObject(formattedTime);// 获取当前签到状态ois4= new ObjectInputStream(socket4.getInputStream());String  status  = (String) ois4.readObject();if (!status.equals(studentStatusMap.get(student))) {// 如果签到状态发生变化，更新 Map，并输出该学生的名字studentStatusMap.put(student, status);if (status.equals("已签到")) {System.out.println(111);success_name=student+" "+success_name;// 在这里执行更新 TableView 的操作Platform.runLater(() -> {updateTableView(check_in_table, "已签到", success_name, formattedTime);initializeTableView_second();initializeTableView_second();System.out.println(23);});}}}// 每隔一秒钟减少一秒Thread.sleep(1000);totalSeconds--;} catch (InterruptedException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();} catch (ClassNotFoundException e) {e.printStackTrace();}}if(totalSeconds <= 0){try {LocalDateTime currentTime2 = LocalDateTime.now();// 格式化当前系统时间，显示年、月、日、时、分和秒DateTimeFormatter formatter2 = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");String formattedTime2 = currentTime2.format(formatter2);oos4.writeObject("111");minutetext.setText("0");second_clocktext.setText("0");Socket socket4 = new Socket("127.0.0.1", 10090);String judgment4 = "teacher_end_check_in";ObjectOutputStream oos4 = new ObjectOutputStream(socket4.getOutputStream());oos4.writeObject(judgment4);      //传送标志oos4.writeObject(formattedTime);oos4.writeObject(formattedTime2);ObjectInputStream ois4 = new ObjectInputStream(socket4.getInputStream());String fail_name = (String) ois4.readObject();Platform.runLater(() -> {updateTableView(check_in_table, "未签到", fail_name, formattedTime2);initializeTableView_second();initializeTableView_second();System.out.println(23);});} catch (IOException e) {e.printStackTrace();} catch (ClassNotFoundException e) {e.printStackTrace();}}// 倒计时结束后执行的逻辑// 这里你可以添加倒计时结束后需要执行的代码});// 启动倒计时线程countdownThread.start();}

签到功能:

随机抽人：