@Override public boolean synchronizedHandleRequest(VaadinSession session, VaadinRequest request, VaadinResponse response) throws IOException { // Find UI class Class<? extends UI> uiClass = getUIClass(request); BootstrapContext context = createAndInitUI(uiClass, request, response, session); ServletHelper.setResponseNoCacheHeaders(response::setHeader, response::setDateHeader); Document document = getBootstrapPage(context); writeBootstrapPage(response, document.outerHtml()); return true; }