数据库需求分析：
class(一级栏目信息）：classId(自动编号），className（栏目名称）
Nclass（二级栏目信息）：NclassId（自动编号），NclassName(栏目名称），parentId（一级栏目id，与class表中的classId关联）
<%@ page contentType="text/html; charset=GB2312" language="java" errorPage="../error.jsp" %>
<%@ include file="../conn.jsp"%>
<%@ include file="../ds.jsp"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/sql" prefix="sql" %>
<%request.setCharacterEncoding("gb2312"); %>
<HTML><HEAD>
<META http-equiv="Content-Type" content="text/html; charset=gb2312">
<TITLE>级联菜单</TITLE>
<LINK rel="stylesheet" type="text/css" href="style.css">
</HEAD>
<!--从数据库中得到二级栏目信息-->
<%String sql="select * from Nclass order by NclassId asc";
ResultSet rs=stmt.executeQuery(sql);
%>
<!--将二级栏目信息保存到数组subcat中-->
<script type="text/javascript">
var onecount;
onecount=0;
subcat = new Array();
<%
int count = 0;
while(rs.next()){
%>
subcat[<%=count%>] = new Array("<%=rs.getString("NclassName")%>","<%=rs.getString("NclassId")%>","<%=rs.getString("parentId")%>");
<%
count++;
}
rs.close();
%>
onecount=<%=count%>;
<!--决定select显示的函数-->
function changelocation(locationid)
{
document.myform.NclassId.length = 0;
var locationid=locationid;
var i;
for (i=0;i < onecount; i++)
{
if (subcat[i][2] == locationid)
{
document.myform.NclassId.options[document.myform.NclassId.length] = new Option(subcat[i][0], subcat[i][1]);
}
}
}
</script>
<FORM method="POST" name="myform" action="adminsave.jsp?action=add">
<TABLE>
<TR>
<TD>一级分类</TD>
<TD>
<SELECT name="classId" onChange="changelocation(document.myform.classId.options[document.myform.classId.selectedIndex].value)" size="1">
<OPTION selected value>==请选一级分类==</OPTION>
<sql:query var="query" dataSource="${bookdev}">
SELECT * FROM class
</sql:query>
<c:forEach var="row" items="${query.rows}">
<option value="${row.classId}">${row.className}</option>
</c:forEach>
</select>
</TD>
<TD>选择二级分类</TD>
<TD>
<SELECT name="NclassId">
<OPTION selected value>==请选二级分类==</OPTION>
</SELECT>
</TD>
</TR>
</TABLE>
</FORM>
</BODY>
</HTML>