Changing favicon dynamically

Hello,
  I would like to change favicon dynamically. Following solution works from Eclipse, but doesn't work, when application is in war file:

class CheckFavicon implements Runnable {

        private final static String faviconScript = "var link = document.createElement('link');\n"
                + "link.type = 'image/x-icon';\n"
                + "link.rel = 'shortcut icon';\n"
                + "link.href = './../VAADIN/themes/PSETheme/%s';\n"
                + "document.getElementsByTagName('head')[0].appendChild(link);";
        
        @Override
        public void run() {
            for (Component component : tabSheet) {
                if (StringUtils.contains(tabSheet.getTab(component).getStyleName(), "alert")) {
                    UI.getCurrent().access(() -> {
                        Page.getCurrent().getJavaScript().execute(String.format(faviconScript, "favicon-red.ico"));
                    });
                    return;
                }
            }
            UI.getCurrent().access(() -> {
                Page.getCurrent().getJavaScript().execute(String.format(faviconScript, "favicon.ico"));
            });
        }
        
    }

Does it exist a way to change it from war file?