There are two methods:
Suppose, the name of this session is adminAccount
1. EL expression
<script type="text/javascript">
if($.trim("${sessionScope.adminAccount}") == "")
{
top.location.href="admin.jsp";
}
</script>
2. java code
<%
if(session.getAttribute("adminAccount")==null || session.getAttribute("adminAccount")=="")
{
String path = request.getContextPath();
String basePath = request.getScheme() + "://"+ request.getServerName() + ":" + request.getServerPort()+ path + "/";
response.sendRedirect(basePath+"admin.jsp");
}
%>