import com.vaadin.annotations.PreserveOnRefresh; //导入依赖的package包/类
@Override
public void modifyBootstrapPage(BootstrapPageResponse response) {
    Document document = response.getDocument();

    Element head = document.getElementsByTag("head").get(0);

    Element element;

    if (isWebAppCapable()) {
        element = document.createElement("meta");
        element.attr("name", "apple-mobile-web-app-capable");
        element.attr("content", "yes");
        head.appendChild(element);
    }

    if (getStatusBarStyle() != null) {
        element = document.createElement("meta");
        element.attr("name", "apple-mobile-web-app-status-bar-style");
        element.attr("content", getStatusBarStyle());
        head.appendChild(element);
    }

    if (getStartupImage() != null) {
        element = document.createElement("link");
        element.attr("rel", "apple-touch-startup-image");
        element.attr("href", getStartupImage());
        head.appendChild(element);
    }

    /*
     * Ensure window has "stable name", in case PreserveOnRefresh is used.
     * This is to fool vaadinBootstrap.js so that for example applications
     * used as ios "home screen webapps", can preserve their state among app
     * switches, like following links (with browser) and then returning back
     * to app.
     */
    if (response.getUiClass().getAnnotation(PreserveOnRefresh.class) != null) {
        element = document.createElement("script");
        element.attr("type", "text/javascript");
        element.appendText("\nwindow.name = '"
                + response.getUiClass().hashCode() + "';\n");
        head.appendChild(element);
    }
}
 

import com.vaadin.annotations.PreserveOnRefresh; //导入依赖的package包/类
/**
 * Vaadin uses the servlet's session mechanism to track users. With its
 * default settings, all sessions will be discarded when the browser
 * application closes. For mobile web applications (such as web apps that
 * are added to the home screen in iOS) this might not be the desired
 * solution.
 * <p>
 * The persistent session cookie is on by default if the UI uses the
 * {@link PreserveOnRefresh} annotation.
 * 
 * @return true if the session cookie will be made persistent when closing
 *         the browser application
 */
public boolean isPersistentSessionCookie() {
    if (persistentSessionCookie != null) {
        return persistentSessionCookie;
    } else {
        UI ui = getUI();
        if (ui != null
                && ui.getClass().getAnnotation(PreserveOnRefresh.class) != null) {
            return true;
        }
    }
    return false;
}