Dynamic Drop-Down Menu Solution

Question

Hi All,
After spending a lot of time trying to find a good solution for a dynamic drop-down menu, I end up writing my own.
The solution is for a list of items, having ITEM as the primary key of the table and ITEMDESCRIPTION as the list of options for the user to select.
The steps are:
1) JavaBean to return a ResultSet;
2) A custom tag to build a HTML SELECT;
3) A .tld file to declare the custom tag;
4) web.xml where the custom tag mapping resides;
4) A JSP to illustrate how to call the custom tag;
Hoping this will save lots of time to others
Cheers
Trajano Roberto
1) Custom tag
package com.amstras.maintenance.customtags;
* Title: erp
* Description:
* Copyright: Copyright (c) 2001
* Company: amstras
* @author Trajano Roberto
* @version 1.0
import javax.servlet.jsp.tagext.*;
import javax.servlet.jsp.*;
import java.sql.*;
import com.amstras.maintenance.javabeans.*;
public class listitemmaster extends TagSupport {
private itemmaster itemmaster = new itemmaster();
private ResultSet rs = null;
private String parametername = null;
public int doStartTag() throws JspException {
try {
itemmaster.connect();
rs = itemmaster.listitemmaster();
pageContext.getOut().print( "<select name = \"" + parametername + "\">" );
catch ( Exception e ) {
throw new JspTagException( e.getMessage() );
finally {
return EVAL_BODY_INCLUDE;
public int doAfterBody() throws JspException {
try {
if( rs.next() ) {
pageContext.getOut().print( "<option value = \"" + rs.getString( "ITEM" ) + "\">" + rs.getString( "ITEM" ) + "&nbsp&nbsp&nbsp" + rs.getString( "ITEMDESCRIPTION" ) + "</option>" );
return EVAL_BODY_AGAIN;
else {
pageContext.getOut().print( "</select>");
itemmaster.disconnect();
return SKIP_BODY;
catch ( Exception e ) {
throw new JspTagException( e.getMessage() );
public void setParametername( String sPARAMETERNAME ) {
parametername = sPARAMETERNAME;
2) JavaBeam where the method to return the ResultSet resides
public ResultSet listitemmaster() throws SQLException, Exception {
if( con != null ) {
try {
String sSQL = null;
sSQL = " SELECT ITEM, ITEMDESCRIPTION FROM ITEMMASTER ORDER BY ITEM ";
ps = con.prepareStatement( sSQL );
rs = ps.executeQuery();
catch( SQLException sqle ) {
error = "SQLException: list item master failed possible record does not exist. ";
error += sqle.toString();
throw new SQLException( error );
catch( Exception e ) {
error = "An exception occured while listing item master record. ";
error += e.toString();
throw new Exception( error );
finally {
return rs;
else {
error = "Exception: Connection to database was lost.";
throw new Exception( error );
3) extract from the .tld file where the custom tag is declared
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE taglib PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN"
"http://java.sun.com/dtd/web-jsptaglibrary_1_2.dtd">
<taglib>
<tlib-version>1.0</tlib-version>
<jsp-version>1.2</jsp-version>
<short-name>itemmaster</short-name>
<description>item master</description>
<tag>
<name>viewitemmaster</name>
<tag-class>com.amstras.maintenance.customtags.viewitemmaster</tag-class>
<attribute>
<name>item</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
<description>item</description>
</attribute>
</tag>
<tag>
<name>listitemmaster</name>
<tag-class>com.amstras.maintenance.customtags.listitemmaster</tag-class>
<attribute>
<name>parametername</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
<description>parameter name</description>
</attribute>
</tag>
</taglib>
4) web.xml mapping for the custom tag
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.2//EN" "http://java.sun.com/j2ee/dtds/web-app_2_2.dtd">
<web-app>
<servlet>
<servlet-name>debugjsp</servlet-name>
<servlet-class>org.apache.jasper.servlet.JspServlet</servlet-class>
<init-param>
<param-name>jspCompilerPlugin</param-name>
<param-value>com.borland.jbuilder.webserverglue.tomcat.jsp.JasperSunJavaCompiler</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>debugjsp</servlet-name>
<url-pattern>*.jsp</url-pattern>
</servlet-mapping>
<taglib>
<taglib-uri>erp/maintenance/itemmaster</taglib-uri>
<taglib-location>/WEB-INF/itemmaster.tld</taglib-location>
</taglib>
</web-app>
5) JSP call to the custom tag
<%@ page errorPage="billofmaterialErrorPage.jsp" %>
<%@ taglib prefix = "im" uri = "erp/maintenance/itemmaster" %>
<html>
<head>
<title>CSI - ERP - add bill of material</title>
<link rel = "stylesheet" href = "/erp/erpstyle.css">
</head>
<body>
<h1>Add Bill of Material</h1>
<form action = "billofmaterialcontroller.jsp" method="post">
<table>
<tr>
<td align = "LEFT"><font color = blue>Parent Item:</font></td>
<td><im:listitemmaster parametername = "parameter1" /></td>
</tr>
<tr>
<td align = "LEFT"><font color = blue>Child Item:</font></td>
<td><im:listitemmaster parametername = "parameter2" /></td>
</tr>
<tr>
<td align = "LEFT"><font color = green>Qty Per:</font></td>
<td><input type = "text" name = "parameter3" size = "5" maxlength = "5" /></td>
</tr>
</table>
<p>
<input type="submit" name="submit" value="Add">
<input type="reset" value="Reset">
</p>
<input type = "hidden" name = "Action" value = "Add">
</form>
Click <a href = "billofmaterial.jsp">here</a> to go back.
</body>
</html>

Answer 1

This is a very helpful execellent sample code.
However, If I'm using Model-View-Control approach, then what's the way of applying these codes
to each indivisual file? Say, I have 20 files and only 4 of the 20 need to be treated as they like
to have drop down menu in particular column(s)??? How could the custom tag be applied as the
controller tells the view to present these special treat? or it is not possible (I have to treat each
file, filtered by controller -- one by one as it encounters the special need)?
Thx, Tzae