Failed to load the bootstrap javascript: ./VAADIN/vaadinBootstrap.js

Vaadin 6 / 7 / 8
39

I have got the following error after adding this add-on to my project.

<dependency>
            <groupId>org.vaadin</groupId>
            <artifactId>countdownclock</artifactId>
            <version>2.0.3</version>
        </dependency>

import java.util.Calendar;
import java.util.Date;

import javax.servlet.annotation.WebServlet;

import org.vaadin.kim.countdownclock.CountdownClock;
import org.vaadin.kim.countdownclock.CountdownClock.EndEventListener;

import com.vaadin.annotations.VaadinServletConfiguration;
import com.vaadin.server.VaadinRequest;
import com.vaadin.server.VaadinServlet;
import com.vaadin.ui.Button;
import com.vaadin.ui.Button.ClickEvent;
import com.vaadin.ui.Button.ClickListener;
import com.vaadin.ui.Label;
import com.vaadin.ui.Notification;
import com.vaadin.ui.UI;
import com.vaadin.ui.VerticalLayout;

public class DemoUI extends UI {

    private static final long serialVersionUID = -2474563921376269949L;

    @WebServlet(value = "demoui", asyncSupported = true)
    @VaadinServletConfiguration(productionMode = false, ui = DemoUI.class)
    public static class Servlet extends VaadinServlet {}

    @Override
    protected void init(VaadinRequest request) {
        final VerticalLayout layout = new VerticalLayout();
        setContent(layout);


        Label label = new Label(
                "Just specify the format of the count down and "
                        + "the date to which to count and you're set to go! "
                        + "Here is an example:");
        layout.addComponent(label);

        layout.addComponent(new Label("One example:"));
        CountdownClock clock2 = new CountdownClock();
        Calendar cal = Calendar.getInstance();
        cal.add(Calendar.SECOND, 10);
        cal.add(Calendar.DAY_OF_MONTH, 2);
        clock2.setDate(cal.getTime());
        clock2.setNeglectHigherUnits(true);
        clock2.setFormat("%s");
        layout.addComponent(clock2);

        layout.addComponent(new Label("...or two.. :"));

        CountdownClock clock1 = new CountdownClock();
        Calendar c = Calendar.getInstance();
        c.set(c.get(Calendar.YEAR) + 1, 0, 1, 0, 0, 0);
        clock1.setDate(c.getTime());
        clock1.setFormat("<span style='font: bold 13px Arial; margin: 10px'>"
                + "Time until new year: %d days, %h hours, %m minutes and %s seconds</span>");
        clock1.setHeight("40px");

        layout.addComponent(clock1);



        final CountdownClock clock = new CountdownClock();
        Button button = new Button("Don't click on me", new ClickListener() {
            private static final long serialVersionUID = -3301865196296699922L;

            public void buttonClick(ClickEvent event) {
                event.getButton().setEnabled(false);
                Calendar c = Calendar.getInstance();
                c.add(Calendar.SECOND, 10);
                clock.setDate(c.getTime());
                clock.setFormat("<span style='font: bold 25px Arial; margin: 10px'>"
                        + "This page will self-destruct in %s.%ts seconds.</span>");

                clock.addEndEventListener(new EndEventListener() {
                    public void countDownEnded(CountdownClock clock) {
                        Notification
                                .show("Ok, implementing the page destruction was"
                                        + " kinda hard, so could you please just imagine"
                                        + " it happening?", Notification.Type.ERROR_MESSAGE);
                    }
                });
                layout.addComponent(clock);
            }
        });
        layout.addComponent(button);
    }
}

i use Vaadin 14.

Failed to load the bootstrap javascript: ./VAADIN/vaadinBootstrap.js?v=8.9.4