SpringMVC拦截器实现监听session是否过期详解

<mvc:interceptors>
  <mvc:interceptor>
    <mvc:mapping path="/**"/>
    <mvc:exclude-mapping path="/user/login"/>  <!-- 不拦截登录请求 -->
    <mvc:exclude-mapping path="/user/logout"/>  <!-- 不拦截注销请求 -->
    <mvc:exclude-mapping path="*.jsp"/>
    <mvc:exclude-mapping path="*.html"/>
    <mvc:exclude-mapping path="*.js"/>
    <mvc:exclude-mapping path="*.css"/>
    <bean class="org.huaxin.interceptor.AccessInterceptor"></bean>
  </mvc:interceptor>
</mvc:interceptors>

public boolean preHandle(HttpServletRequest request, HttpServletResponse response,
      Object obj) throws Exception {
    System.out.println("[AccessInterceptor]:preHandle执行");
    HttpSession session = request.getSession();
    ServletContext application = session.getServletContext();
    if(application.getAttribute(session.getId()) == null){  //未登录
      PrintWriter out = response.getWriter();
      StringBuffer sb = new StringBuffer("<script type=\"text/javascript\" charset=\"UTF-8\">");
      sb.append("alert(\"你的账号被挤掉，或者没有登录，或者页面已经过期，请重新登录\")");
      sb.append("window.location.href='/user/logout';");
      sb.append("</script>");
      out.print(sb.toString());
      out.close();
      return false;
    }else{  //已经登录
      return true;
    }
  }