Vaadin 7.3.2中没有会话过期通知

Question

我在OSGI中使用Vaadin 7.3.2，所有vaadin包都是活动的。当服务器关闭时，页面中没有会话过期通知。你能帮帮我吗...

<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    id="vaadin-portal" version="2.5">
    <display-name>Vaadin Web Application</display-name>
    <context-param>
        <description>Vaadin production mode</description>
        <param-name>productionMode</param-name>
        <param-value>false</param-value>
    </context-param>
    <servlet>
        <servlet-name>Portal Vaadin App</servlet-name>
        <servlet-class>com.vaadin.server.VaadinServlet</servlet-class>
        <init-param>
            <description>Vaadin UI</description>
            <param-name>UI</param-name>
            <param-value>com.example.MainUI</param-value>
        </init-param>
        <async-supported>true</async-supported>
    </servlet>
    <servlet-mapping>
        <servlet-name>Portal Vaadin App</servlet-name>
        <url-pattern>/*</url-pattern>
    </servlet-mapping>
</web-app>