上下文问题(很简单的)

ServletContext context = getServletContext();       //这容器有什么用
        Integer count = (Integer) context.getAttribute("counter");  //counter哪来的
        if(count==null)
        {
            count = new Integer(1);
        }else{
            count = new Integer(count.intValue()+1);
        }
        context.setAttribute("counter", count);                     //设置counter的属性是什么意思