<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;
        }
    }