JSP + JavaScript creates a level-2 cascade drop-down menu:
Class (first-level column information): classId (automatic number), className (column name), Nclass (second-level column information), NclassId (automatic number), NclassName (column name ), parentId (first-level column id, associated with classId in the class table)
Reference content is as follows:
<% @ Page contentType = text/html; charset = GB2312 language = java errorPage =.../error. jsp %>
<% @ Include file = ../conn. jsp %>
<% @ Include file = ../ds. jsp %>
& Lt; % @ taglib uri = http://java.sun.com/jsp/jstl/ SQL divfix = SQL % & gt;
<% Request. setCharacterEncoding (gb2312); %>
<HTML> <HEAD>
<META http-equiv = Content-Type content = text/html; charset = gb2312> <TITLE> cascade menu </TITLE>
<LINK rel = stylesheet type = text/css href?style.css>
</HEAD>
<! -- Obtain the second-level column information from the database -->
<% String SQL = select * from Nclass order by NclassId asc;
ResultSet rs1_stmt.exe cuteQuery (SQL );
%>
<! -- Save the second-level column information to the array subcat -->
<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 %>;
<! -- Determines the function displayed by select -->
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> Level 1 Classification </TD>
<TD>
<SELECT name = classId onChange = changelocation (document. myform. classId. options
[Document. myform. classId. selectedIndex]. value) size = 1>
<OPTION selected value >== select a level-1 category ==</OPTION>
<SQL: query var = query dataSource =$>
SELECT * FROM class
</SQL: query>
<C: forEach var = row items = $>
<Option value =$ >$ </option>
</C: forEach>
</Select>
</TD>
<TD> Select secondary category </TD>
<TD>
<SELECT name = NclassId>
<OPTION selected value >== select Level 2 Category ==</OPTION>
</SELECT>
</TD>
</TR>
</TABLE>
</FORM>
</BODY>
</HTML>
<% @ Page contentType = text/html; charset = GB2312 language = java errorPage =.../error. jsp %>
<% @ Include file = ../conn. jsp %>
<% @ Include file = ../ds. jsp %>
& Lt; % @ taglib uri = http://java.sun.com/jsp/jstl/ SQL divfix = SQL % & gt;
<% Request. setCharacterEncoding (gb2312); %>
<HTML> <HEAD>
<META http-equiv = Content-Type content = text/html; charset = gb2312> <TITLE> cascade menu </TITLE>
<LINK rel = stylesheet type = text/css href?style.css>
</HEAD>
<! -- Obtain the second-level column information from the database -->
<% String SQL = select * from Nclass order by NclassId asc;
ResultSet rs1_stmt.exe cuteQuery (SQL );
%>
<! -- Save the second-level column information to the array subcat -->
<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 %>;
<! -- Determines the function displayed by select -->
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> Level 1 Classification </TD>
<TD>
<SELECT name = classId onChange = changelocation (document. myform. classId. options
[Document. myform. classId. selectedIndex]. value) size = 1>
<OPTION selected value >== select a level-1 category ==</OPTION>
<SQL: query var = query dataSource =$>
SELECT * FROM class
</SQL: query>
<C: forEach var = row items = $>
<Option value =$ >$ </option>
</C: forEach>
</Select>
</TD>
<TD> Select secondary category </TD>
<TD>
<SELECT name = NclassId>
<OPTION selected value >== select Level 2 Category ==</OPTION>
</SELECT>
</TD>
</TR>
</TABLE>
</FORM>
</BODY>
</HTML>
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