Access database query resultset in java scriptlet

Question

Question:
1) I am Creating a web page and plotting points on the page:
2) Database query results in decimal values dec_latitude and dec_longiitude.
3) Perform calculations on lati. & long. in a java scriptlet to create a plot position (xpos, ypos).
4) Send the xpos and ypos back to the java server page
5) Use <IMG and absolute positioning to plot the point at position xpos, and ypos.
6) Repeat until all rows in the query result set have been plotted.
I don't know how to pass the dec_latitude and dec_longitude to the java scriptlet.
After the java scriptlet calculation translates the latitude and longitude
into xpos and ypos, I need to pass the xpos and ypos back to the java server page so that a data point is plotted on a map at position xpos, ypos.
I tried many ways of doing it but am just guessing as
to how to pass the data.
Thanks in Advance. - John
Here is what I am trying so far .... see snippet below:
The code below results in a runtime error.
Am I supposed to create a java object and access that in the java scriptlet? Can the java scriptlet access the latvar and longvar created during the "<c:set var="latvar"... ?
If not, what mechanisum do I use to access the resulting colums: dec_latitude and dec_longitude? I need the java scriptlet to convert the
dec_latitude and dec_longitude into a display position based on the number of pixels from the TOP and LEFT (xpos, ypos). Then plot of the data point using the IMG and (xpos, ypos). This will overlay a map whose z-index is lower than the plotted data point.
*** Query the database ***
<sql:query var="qryBio">
SELECT
DEC_LATITUDE,
DEC_LONGITUDE,
ENTRY_TIMESTAMP
FROM app.biosurvey where
</sql:query>
*** for each row retreived from the database ***
<c:forEach var="row" items="${qryBio.rows}">
<c:set var="latvar" value="${row.dec_latitude}" scope="page"/>
<c:set var="longvar" value="${row.dec_longitude} "scope="page" />
*** java code scriptlet - ***
*** convert latitude and longitude to xpos and ypos for display ***
<%
latitude = (Float)pageContext.getAttribute("latvar"); <--- runtime error !!!!
longitude = (Float)pageContext.getAttribute("longvar");
xpos = (int)Math.round(latitude);
ypos = (int)Math.round(longitude);
xpos = 1082 - xpos;
ypos = 700 + ypos;
pageContext.setAttribute("xpos", xpos);
pageContext.setAttribute("ypos", ypos);
%>
*** plot a point on the display html page overlaying the map ***
<IMG ID="Row" SRC="smallredbox.jpg" ALT="red box"
STYLE="position:absolute;
top:<%=xpos%> px;
left:<%=ypos%> px;
z-index:2">
</c:forEach>

Answer 1

Thanks
I still get a runtime error: I translated the code you gave to code below .... which I think is equivalent. See Below: I'm still learning about this stuff so I may not have not translated this properly. Do
you see what I am doing wrong?
Best Regards,
- John
%@ page language="java" contentType="text/html;
charset=ISO-8859-1"%>
<%@ taglib prefix="sql" uri="http://java.sun.com/jsp/jstl/sql"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<%@ page import="java.lang.Math"%>
<sql:setDataSource dataSource="jdbc/SampleDB" />
<c:set var="genus_name" value="${param.genus_name}" />
<c:set var="species_name" value="${param.species_name}" />
<c:set var="species_common_name" value="${param.species_common_name}" />
<c:set var="dd_sighted" value="${param.dd_sighted}" />
<c:set var="mm_sighted" value="${param.mm_sighted}" />
<c:set var="yyyy_sighted" value="${param.yyyy_sighted}" />
<c:set var="species_state" value="${param.species_state}" />
<c:set var="species_county" value="${param.species_county}" />
<c:set var="species_country" value="${param.species_country}" />
<c:set var="dec_latitude" value="${param.dec_latitude}" />
<c:set var="dec_longitude" value="${param.dec_longitude}" />
<c:set var="notes" value="${param.notes}" />
<c:set var="person_first_name" value="${param.person_first_name}" />
<c:set var="person_last_name" value="${param.person_last_name}" />
<c:set var="person_street" value="${param.person_street}" />
<c:set var="person_city" value="${param.person_city}" />
<c:set var="person_state" value="${param.person_state}" />
<c:set var="person_zip" value="${param.person_zip}" />
<c:set var="person_country" value="${param.person_country}" />
<c:set var="person_email" value="${param.person_email}" />
<h2>Species Sightings:</h2>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Breckenridge Citizen Bio-Survey Selective Output Page</title>
</head>
<body>
Izaak Walton League of America
<h1>Breckenridge Citizen Bio-Survey Selective Output</h1>
<HR>
<c:if test="${param.action == 'Submit'}">
<%int xpos = 0;
     int ypos = 0;
     float latitude = 0.0F;
     float longitude = 0.0F;
     float latitudeMpls = 45.06F;
     float longitudeMpls = -93.14F;                    int xposMpls = 1205 - (int) Math.round(latitudeMpls);
     int yposMpls = 735 + (int) Math.round(longitudeMpls);
%>
<IMG SRC="minnesota_1990.jpg" ALT="minesota map" style="z-index:1;"> <----- THIS WORKS FINE
<IMG ID="Row" SRC="smallredbox.jpg" ALT="red box"
STYLE="position:absolute;
top:<%=xposMpls%> px;
left:<%=yposMpls%> px;
z-index:2"> <----- THIS WORKS FINE FOR HARDCODED MPLS XPOS AND YPOS
<sql:query var="qryBio">
SELECT
PERSON_FIRST_NAME,
PERSON_LAST_NAME,
GENUS_NAME,
SPECIES_NAME,
SPECIES_COMMON_NAME,
SPECIES_COUNTY,
SPECIES_STATE,
SPECIES_COUNTRY,
DD_SIGHTED,
MM_SIGHTED,
YYYY_SIGHTED,
DEC_LATITUDE,
DEC_LONGITUDE,
NOTES,
ENTRY_TIMESTAMP
FROM app.biosurvey where
genus_name like rtrim(upper('${genus_name}')) AND
species_name like rtrim(upper('${species_name}')) AND
species_common_name like rtrim(upper
('${species_common_name}')) AND
species_state like rtrim(upper('${species_state}')) AND
species_county like rtrim(upper('${species_county}')) AND
species_country like rtrim(upper('${species_country}')) AND
person_first_name like rtrim(upper('${person_first_name}')) AND
person_last_name like rtrim(upper('${person_last_name}')) AND
person_email like rtrim(upper('${person_email}'))
</sql:query>
<c:forEach var="row" items="${qryBio.rows}">
<--- THE LINE ABOVE WORKS FINE --->
<c:set var="latvar" value="${row.dec_latitude}" scope="page" />
<c:set var="longvar" value="${row.dec_longitude} " scope="page" />
<%
latitude =
Float.parseFloat((String)pageContext.getAttribute("latvar"));
<--- RUNTIME ERROR OCCURS HERE --- SEE LINE ABOVE --->
longitude =
Float.parseFloat((String)pageContext.getAttribute("longvar"));
xpos = (int) Math.round(latitude);
ypos = (int) Math.round(longitude);
xpos = 1082 - xpos;
ypos = 700 + ypos;
request.setAttribute("xpos",new Integer(xpos));
request.setAttribute("ypos",new Integer(ypos));
%>
IIMG ID="Row" SRC="smallredbox.jpg" ALT="red box"
STYLE="position:absolute;
top:<%=xpos%> px;
left:<%=ypos%> px;
z-index:2">
<--- THIS (ABOVE) WORKS FINE WITH CORRECT VALUES FOR XPOS AND YPOS WHEN RUNTIME ERROR DOES NOT OCCUR --->
</c:forEach>
</c:if>