Prototype of session timeout warning dialog

PushBased.java

package org.vaadin.vaadin.sb.example.views;

import com.vaadin.flow.component.AttachEvent;
import com.vaadin.flow.component.DetachEvent;
import com.vaadin.flow.component.UI;
import com.vaadin.flow.component.button.Button;
import com.vaadin.flow.component.html.Paragraph;
import com.vaadin.flow.component.html.Span;
import com.vaadin.flow.component.orderedlayout.VerticalLayout;
import com.vaadin.flow.router.Route;
import com.vaadin.flow.server.VaadinSession;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import java.util.logging.Level;
import java.util.logging.Logger;

@Route
public class PushBased extends VerticalLayout {

    private static ScheduledExecutorService ses = Executors.newScheduledThreadPool(1);

    private Span currentTimeout;
    private int sessionInSeconds;

    public PushBased() {
        Button button = new Button("Click me",
                event -> add(new Paragraph("Clicked!")));

        add(button);

    }

    @Override
    protected void onAttach(AttachEvent attachEvent) {
        super.onAttach(attachEvent);

        Logger.getLogger(getClass().getSimpleName()).info("Attached MainView");

        UI ui = attachEvent.getUI();
        sessionInSeconds = VaadinSession.getCurrent().getSession().getMaxInactiveInterval();

        ses.scheduleAtFixedRate(() -> {

            Logger.getLogger(getClass().getSimpleName()).log(Level.INFO, "Scheduler check request for UI {0} in session {1}", new Object[]{ui.getUIId(), ui.getSession().getSession().getId()});

            try {

                if (!ui.isAttached()) {
                    Logger.getLogger(getClass().getSimpleName()).log(Level.INFO, "UI {0}, is not attached!", new Object[]{ui.getUIId()});
                    throw new RuntimeException("Stop this task...");
                }

                ui.access(() -> {
                    long lastAccessedTime = ui.getSession().getLastRequestTimestamp();
                    Logger.getLogger(getClass().getSimpleName()).log(Level.INFO, "UI {0}, last access: {1}", new Object[]{ui.getUIId(), lastAccessedTime});

                    long now = System.currentTimeMillis();
                    // use f (float) for better handling of seconds
                    float secondsSinceLastAction = (now - ui.getSession().getLastRequestTimestamp()) / 1000f;
                    // use round to allow 0.7 to be 1 and 1.7 to be 2
                    int secondsToLogout = (sessionInSeconds - Math.round(secondsSinceLastAction));

                    updateCurrentTimeout(secondsToLogout);

                    if (secondsToLogout > 2) {
                        return; // 'auto save should only happen if minutesTilLogout == 1'
                    }

                    if (secondsToLogout == 2) {

                    }

                    if (secondsToLogout <= 1) {

                    }
                });
            } catch (Exception e) {
                Logger.getLogger(getClass().getSimpleName()).log(Level.INFO, "ERROR", e);
                throw e;
            }

        }, 1, 1, TimeUnit.SECONDS);

    }

    @Override
    protected void onDetach(DetachEvent detachEvent) {
        super.onDetach(detachEvent);
        Logger.getLogger(getClass().getSimpleName()).info("Detached MainView");
    }

    private void updateCurrentTimeout(int minutesTilLogout) {
        var text = minutesTilLogout + " seconds of session remaining";
        if (null == currentTimeout) {
            add(currentTimeout = new Span(text));
        } else {
            currentTimeout.setText(text);
        }
    }

}