网页后退过期的实现
加入以下代码即可：

        <META http-equiv="Expires" content="0"/><META http-equiv="Cache-Control" content="no-store, no-cache, must-revalidate"/>  <META http-equiv="Pragma" content="no-cache"/> <%response.setHeader("Pragma","no-cache"); response.setHeader("Cache-Control","no-store, no-cache, must-revalidate"); response.setDateHeader("Expires", 0);%>