How to populate the combo boxes that are created dynamically in jsp

Question

Hi,
I am using JSP.
I am creating combo boxes dynamically (based on the num selected by the user). These dynamically created combo boxes need to have A-Z as options (each box) . Now, when the user chooses the option A in any of the combo-boxes,the rest should not have this option. so on..
how do i achieve this.Kindly help.

Answer 1

You'll need to use JavaScript...I have a complicated example and a simple example, however, I cannot really understand the complex example but I know how it works. The looping is too complex for me.
First you'll need to populate a server side variable...depending on how often the data is updated you may want this to run each time a new session is created...this example is run each time Tomcat is started and the application context is initialized:
package kms.web;
// Servlet imports
import javax.servlet.ServletContextListener;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContext;
// utility imports
import java.util.Map;
// domain imports
import kms.domain.LocationService;
import kms.domain.DeptService;
import kms.domain.PatentService;
* This listenter is used to initialize
* the Maps of Locations, Patents & Depts used to populate
* pulldown lists in JSPs
public class InitializeData implements ServletContextListener {
    * This method creates the Maps.
   public void contextInitialized(ServletContextEvent sce) {
      ServletContext context = sce.getServletContext();
      LocationService lServ = new LocationService();
      // Create the Maps
      Map campuses = lServ.getCampuses();
      Map buildings = lServ.getBuildings();
      Map floors = lServ.getFloors();
      Map locs = lServ.getLocations();
      // And store them in the "context" (application) scope
      context.setAttribute("campuses", campuses);
      context.setAttribute("buildings", buildings);
      context.setAttribute("floors", floors);
      context.setAttribute("locs", locs);
      DeptService dServ = new DeptService();
      Map depts = dServ.getDepts();
      context.setAttribute("depts", depts);
      PatentService pServ = new PatentService();
      Map patents = pServ.getPatents();
      context.setAttribute("patents", patents);
      //I did this one myself
/*    CodeService cServ = new CodeService();
      Map masterMks = cServ.getCodes();
      context.setAttribute("masterMks", masterMks);
    * This method is necessary for interface.
   public void contextDestroyed(ServletContextEvent sce) {
   // I have no clue what the heck this is for???
   // Let me know if you do!
}So now we travel into the PatentService method called 'getPatents();' which in turn calls a PatentDAO method
Map patents = pServ.getPatents();
Below is the code for the PatentService object:
package kms.domain;
import kms.util.ObjectNotFoundException;
import java.util.*;
* This object performs a variety of dept services, like retrieving
* a dept object from the database, or creating a new dept object.
public class PatentService {
   * The internal Data Access Object used for database CRUD operations.
  private PatentDAO patentDAO;
   * This constructor creates a Dept Service object.
  public PatentService() {
    patentDAO = new PatentDAO();
public Map getPatents() {
      Map patents = null;
      try {
        patents = patentDAO.retrieveAll();
      // If the dept object does not exist, simply return null
      } catch (ObjectNotFoundException onfe) {
        patents = null;
      return patents;
}It may be useful for you to see the code of the Patent class:
package kms.domain;
/*** This domain object represents a dept.
public class Patent implements java.io.Serializable {
  private int codeGgm;
  private String name = "";
  private String description = "";
  private int creator;
  private String creationDate = "";
  private int used;
   * This is the full constructor.
  public Patent(int codeGgm, String name, String desc, int creator, String creationDate, int used) {
    this.codeGgm = codeGgm;
    this.name = name;
    this.description = desc;
    this.creator = creator;
    this.creationDate = creationDate;
    this.used = used;
  public Patent() { }
  public int getCodeGgm() {
      return codeGgm;
  public void setCodeGgm(int codeGgm) {
       this.codeGgm = codeGgm;
  public String getName() {
    return name;
  public void setName(String name) {
      this.name = name;
  public String getDesc() {
    return description;
  public void setDesc(String desc) {
      this.description = desc;
  public int getCreator() {
      return creator;
  public void setCreator(int creator) {
         this.creator = creator;
  public String getCreationDate() {
      return creationDate;
  public void setCreationDate(String creationDate) {
         this.creationDate = creationDate;
  public int getUsed() {
       return used;
  public void setUsed(int used){
       this.used = used;
}And here is the Database table which stores the Patents:
DESC PATENT:
CODE_GGM NUMBER(3)
NAME VARCHAR2(15)
DESCRIPTION VARCHAR2(250)
CREATOR NUMBER(10)
CREATION_DATE DATE
USED NUMBER(1)
So, we then travel into the code of the PatentDAO to see how the DAO object executes the DB query to get all of the Data we need for the select list:
package kms.domain;
import javax.naming.*;
import javax.sql.*;
import java.util.*;
import java.sql.*;
import kms.util.*;
* This Data Access Object performs database operations on Patent objects.
class PatentDAO {
   * This constructor creates a Patent DAO object.
   * Keep this package-private, so no other classes have access
PatentDAO() {
* This method returns a Map of all the Dept names
* The key is the Dept id
Map retrieveAll()
       throws ObjectNotFoundException {
      Connection connection = null;
      ResultSet results = null;
      // Create the query statement
      PreparedStatement query_stmt = null;
      try {
        // Get a database connection
      Context initContext = new InitialContext();
       DataSource ds = (DataSource)initContext.lookup("java:/comp/env/jdbc/keymanOracle");
       connection = ds.getConnection();
        // Create SQL SELECT statement
        query_stmt = connection.prepareStatement(RETRIEVE_ALL_NAMES);
        results = query_stmt.executeQuery();
        int num_of_rows = 0;
      Map patents = new TreeMap();
         // Iterator over the query results
        while ( results.next() ) {
            patents.put(new Integer(results.getInt("code_ggm")), results.getString("name"));
         if ( patents != null ) {
                  return patents;
                } else {
                  throw new ObjectNotFoundException("patent");
       // Handle any SQL errors
     } catch (SQLException se) {
        se.printStackTrace();
       throw new RuntimeException("A database error occured. " + se.getMessage());
    } catch (NamingException se) {
      throw new RuntimeException("A JNDI error occured. " + se.getMessage());
      // Clean up JDBC resources
      } finally {
        if ( results != null ) {
          try { results.close(); }
          catch (SQLException se) { se.printStackTrace(System.err); }
        if ( query_stmt != null ) {
          try { query_stmt.close(); }
          catch (SQLException se) { se.printStackTrace(System.err); }
        if ( connection != null ) {
          try { connection.close(); }
          catch (Exception e) { e.printStackTrace(System.err); }
private static final String RETRIEVE_ALL_NAMES
      = "SELECT code_ggm, name FROM patent ";
}Now when you wish to use the 'combo box' (also called select lists), you insert this code into your jsp:
<TR>
<%@ include file="../incl/patent.jsp" %>
</TR>
depending on how your files on your server are organized, the "../incl/patent.jsp"
tells the container to look up one directory from where the main jsp is to find the 'patent.jsp' file in the 'incl' directory.
I need some help creating multi-level select lists with JavaScript:
Can anyone explain this code:
<%@ page import="java.util.*,kms.domain.*" %>
<jsp:useBean id="campuses" scope="application" class="java.util.Map" />
<TR><TD ALIGN='right'>Campus: </TD>
<TD>
<select name="campus" size="1" onChange="redirect(this.options.selectedIndex)">
<option value="0" selected>No Campus</option>
<% LocationService ls = new LocationService();
   Iterator c = campuses.keySet().iterator();
   Map[] bm = new Map[campuses.size()];
   Map[][] fm = new Map[campuses.size()][0];
   Map[][][] lm = new Map[campuses.size()][0][0];
   int i2 = 0;
   int j2 = 0;
   int k2 = 0;
   int jj = 0;
   int kk = 0;
   while (c.hasNext()) {
      Integer i = (Integer)c.next();
      out.print("<OPTION ");
      out.print("VALUE='" + i.intValue()+ "'>");
      out.print( (String) campuses.get(i) );
      out.print("</OPTION>");
      bm[i2] =  ls.getBuildingsByCampus(i.intValue());
      fm[i2] = new Map[bm[i2].size()];
      lm[i2] = new Map[bm[i2].size()][];
      Iterator b = bm[i2].keySet().iterator();
      j2 = 0;
      while (b.hasNext()) {
        Integer j = (Integer)b.next();
        fm[i2][j2] = ls.getFloorsByBuilding(j.intValue());
        lm[i2][j2] = new Map[fm[i2][j2].size()];
        Iterator f = fm[i2][j2].keySet().iterator();
        k2 = 0;
        while (f.hasNext()) {
          Integer k = (Integer)f.next();
          lm[i2][j2][k2] = ls.getLocationsByFloor(k.intValue());
          k2++;
          kk++;
        j2++;
        jj++;
      i2++;
   } %>
</select></TD>
</TR>
<TR><TD ALIGN='right'>Building: </TD>
<TD>
<select name="building" size="1" onChange="redirect1(this.options.selectedIndex)">
<option value="0" selected>No Building</option>
</select></TD>
</TR>
<TR><TD ALIGN='right'>Floor: </TD>
<TD>
<select name="floor" size="1" onChange="redirect2(this.options.selectedIndex)">
<option value="0" selected>No Floor</option>
</select></TD>
</TR>
<TR><TD ALIGN='right'>Room: </TD>
<TD>
<select name="location_id" size="1">
<option value="0" selected>No Room</option>
</select></TD>
</TR>
<script>
var cNum = <%=i2%>
var bNum = <%=jj%>
var fNum = <%=kk%>
var cc = 0
var bb = 0
var ff = 0
var temp=document.isc.building
function redirect(x){
cc = x
for (m=temp.options.length-1;m>0;m--)
  temp.options[m]=null
  temp.options[0]=new Option("No Building", "0")
  if (cc!=0) {
    for (i=1;i<=group[cc-1].length;i++){
      temp.options=new Option(group[cc-1][i-1].text,group[cc-1][i-1].value)
temp.options[0].selected=true
redirect1(0)
var group=new Array(cNum)
for (i=0; i<cNum; i++) {
group[i]=new Array()
<% for (int i=0; i< bm.length; i++) {
Iterator bldgs = bm[i].keySet().iterator();
int j = 0;
while (bldgs.hasNext()) {
Integer intJ =(Integer) bldgs.next(); %>
group[<%=i%>][<%=j%>] = new Option("<%=bm[i].get(intJ)%>", "<%=intJ%>");
<% j++;
} %>
var group2=new Array(cNum)
for (i=0; i<cNum; i++) {
group2[i] = new Array()
for (j=0; j<=bNum; j++) {
group2[i][j] = new Array()
<% for (int i=0; i< fm.length; i++) {
for (int j=0; j< fm[i].length; j++) {
Iterator flrs = fm[i][j].keySet().iterator();
int k = 0;
while (flrs.hasNext()) {
Integer intK =(Integer) flrs.next(); %>
group2[<%=i%>][<%=j%>][<%=k%>] = new Option("<%=fm[i][j].get(intK)%>", "<%=intK%>");
<% k++;
} %>
var temp1=document.isc.floor
var camp=document.isc.campus.options.selectedIndex
function redirect1(x){
bb = x
for (m=temp1.options.length-1;m>0;m--)
temp1.options[m]=null
temp1.options[0]=new Option("No Floor", "0")
if (cc!=0 && bb!=0) {
for (i=1;i<=group2[cc-1][bb-1].length;i++){
temp1.options[i]=new Option(group2[cc-1][bb-1][i-1].text,group2[cc-1][bb-1][i-1].value)
temp1.options[0].selected=true
redirect2(0)
var group3=new Array(cNum)
for (i=0; i<cNum; i++) {
group3[i] = new Array()
for (j=0; j<=bNum; j++) {
group3[i][j] = new Array()
for (k=0; k<=fNum; k++) {
group3[i][j][k] = new Array()
<% for (int i=0; i< lm.length; i++) {
for (int j=0; j< lm[i].length; j++) {
for (int k=0; k< lm[i][j].length; k++) {
Iterator locs = lm[i][j][k].keySet().iterator();
int m = 0;
while (locs.hasNext()) {
Integer intM =(Integer) locs.next(); %>
group3[<%=i%>][<%=j%>][<%=k%>][<%=m%>] = new Option("<%=lm[i][j][k].get(intM)%>", "<%=intM%>");
<% m++;
} %>
var temp2=document.isc.location_id
function redirect2(x){
ff = x
for (m=temp2.options.length-1;m>0;m--)
temp2.options[m]=null
temp2.options[0]=new Option("No Room", "0")
if (cc!=0 && bb!=0 && ff!=0) {
for (i=1;i<=group3[cc-1][bb-1][ff-1].length;i++){
temp2.options[i]=new Option(group3[cc-1][bb-1][ff-1][i-1].text,group3[cc-1][bb-1][ff-1][i-1].value)
temp2.options[0].selected=true
</script>
This produces a related select list with 4 related lists by outputting JavaScript to the page being served. It works the same way as the first example that I describe but I don't understand the looping...maybe someone could explain how to go from the single select list to a double and/or triple level drill down?