Java FX输入字段的错误异常处理，请确保该字段只接受正整数

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Alert;
import javafx.scene.control.Alert.AlertType;
import javafx.scene.control.TextField;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class IntegerTextFieldExample extends Application {

    @Override
    public void start(Stage primaryStage) {
        TextField textField = new TextField();
        textField.textProperty().addListener((observable, oldValue, newValue) -> {
            try {
                int value = Integer.parseInt(newValue);
                if (value <= 0) {
                    throw new NumberFormatException();
                }
            } catch (NumberFormatException e) {
                showAlert("错误", "请输入一个正整数！");
                textField.setText(oldValue);
            }
        });

        VBox root = new VBox(textField);
        Scene scene = new Scene(root, 200, 100);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    private void showAlert(String title, String message) {
        Alert alert = new Alert(AlertType.ERROR);
        alert.setTitle(title);
        alert.setHeaderText(null);
        alert.setContentText(message);
        alert.showAndWait();
    }

    public static void main(String[] args) {
        launch(args);
    }
}