SiteVaadinServlet.java

package org.bubblecloud.ilves.site;

import com.vaadin.server.*;
import org.jsoup.nodes.Attributes;
import org.jsoup.nodes.Element;
import org.jsoup.parser.Tag;

import javax.servlet.ServletException;

public class SiteVaadinServlet extends VaadinServlet {
    @Override
    protected void servletInitialized() throws ServletException {
        getService().addSessionInitListener(new SessionInitListener() {
            @Override
            public void sessionInit(final SessionInitEvent event) {
                event.getSession().addBootstrapListener(
                        new BootstrapListener() {

                            @Override
                            public void modifyBootstrapPage(
                                    BootstrapPageResponse response) {

                                // Add viewport meta tag
                                Attributes attr = new Attributes();
                                attr.put("name", "viewport");
                                attr.put("content",
                                        "width=device-width, initial-scale=1");
                                response.getDocument()
                                        .head()
                                        .appendChild(
                                                new Element(
                                                        Tag.valueOf("meta"),
                                                        "", attr));

                            }

                            @Override
                            public void modifyBootstrapFragment(
                                    BootstrapFragmentResponse response) {
                            }
                        });
            }
        });
        super.servletInitialized();
    }
}