Shawn Bayern wrote:
On Sun, 3 Nov 2002, Stefan wrote:
I am looking for information how the JSTL ResultObject deals with
caching of resultsets derived from a Javabean method that returned a
JDBC's rowset. When is the resultObject removed from memory, and/or
how (if it is cached), can it be controlled?
There are really questions for the JVM, not for application developers.
The object is eligible for removal once no references point to it; its
space can be recovered as soon as a page that created it in page scope
goes out of scope, for instance (or when a session expires, if it's stored
in session scope -- and so forth).
In a situation where I have a resultset that is displayed in a jsp
using the JSTL <c:forEach> tag how can I set it up so that the
resultsObject persist for say 1 minute so that when the page is loaded
we don't have to go back to the database every time?
This is a broader question; it's not the responsibility of the Result
object to "cache" results in this fashion. (It simply stores and "caches"
results with a lifecycle associated with that of the object.)
You can use the Jakarta Taglibs "Cache Taglib" -- or other projects'
alternatives -- if you want open-ended, time-based caching.
Adding another alternative, assuming you do the SQL query in the JSP
page. This is a simple caching technique I describe in my book, using
only JSTL and standard actions:
<!-- Set the chache period to one minute -->
<c:set var="cachePeriod" value="${1 * 60 * 1000}" />
<jsp:useBean id="now" class="java.util.Date" />
<c:if test="${(now.time - cacheTime) > cachePeriod}">
<sql:query var="result" scope="session" sql="..." />
<c:set var="cacheTime" value="${now.time}" scope="session" />
</c:if>
This snippet makes sure you only access the database for a request
received at least one minute after the last time you processed the
query.
If you access the database in a servlet or a bean instead, you
can translate this logic into Java code.
Hans
--
Hans Bergsten [EMAIL PROTECTED]
Gefion Software http://www.gefionsoftware.com
JavaServer Pages http://TheJSPBook.com
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