Page by Page Iterator

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Page by Page Iterator

Page by Page Iterator

2003-11-21 - By Kancharlapalli,Sridhar

Back

Reply: 1 2 3 4 5 6

Hi,

Let me try to elaborate some of my observations and solutions I applied in the
projects I have done.

We had similar problem as you mentioned, Large queries can be really be
expensive as they deal with large data,this makes the ValueListHandler pattern
hard to implement. And more over requering might induct or remove some of the
previous results which might not be acceptable in all business process.

Best way to do it is to get the initial results from DAO layer and cache them
at the client and use a simple Iterator pattern for page navigation. To
optimize the results you can retrieve only the key elements from DAO and cache
them at client. And you would do a complete query for only those set of records
that are to be displayed in the page.

-Sridhar Kancharlapalli.

Hi all,

Some questions regarding the page by page iterator pattern.

I learnt how this patterns works looking at the petstore application. Then I
tried to search on google a full description of this pattern, but I found only
one document in spanish.

First question. Can anyone of you send me a link with a full description of
this pattern?

Second question.

I have a DAO layer which perform a specific JDBC query Q that returns a set of
data of
type T.
Now I want display this result page by page. If I use the Page by Page Iterator
pattern, the query Q will be executed each time the user switch from a page to
another (each time the
start point of the cursor in the Resultset will change). But this is not
acceptable if the query is very expansive.

I read a thread on theserverside.com but I do not understand what to do in this
case.
I think that the Page by Page Iterator is not appropriate in this case.

Third Question. Is it possible combine the Page by Page solution with another
pattern that is more appropriate for complex queries? In this way the client
know that the result is paged
but it do not know how this paging is implemented (Page by Page or other
patterns).

Thanks in advance for any help. ===============================================
===================== Companion Site: http://www.corej2eepatterns.com J2EE
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====================================================================
Companion Site: http://www.corej2eepatterns.com
J2EE BluePrints: http://java.sun.com/blueprints/corej2eepatterns
List Archive: http://archives.java.sun.com/archives/j2eepatterns-interest.html
Unsubscribing: email "signoff J2EEPATTERNS-INTEREST" to listserv@(protected)

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859 (See http://iso-8859.ora-code.com)-1">
<TITLE></TITLE>

<META content="MSHTML 5.00.3502.5390" name=GENERATOR></HEAD>
<BODY bgColor=#ffffff text=#000000>
<BLOCKQUOTE>
<DIV align=left class=OutlookMessageHeader dir=ltr>Hi,</DIV>
<DIV align=left class=OutlookMessageHeader dir=ltr> </DIV>
<DIV align=left class=OutlookMessageHeader dir=ltr>Let me try to
elaborate some of my observations and solutions I applied in the projects I
have done.</DIV>
<DIV align=left class=OutlookMessageHeader dir=ltr> </DIV>
<DIV align=left class=OutlookMessageHeader dir=ltr>We had similar problem as you
mentioned, Large queries can be really be expensive as they deal with
large data,this makes the ValueListHandler pattern hard to implement. And
more
over requering might induct or remove some of the previous results which
might
not be acceptable in all business process.</DIV>
<DIV align=left class=OutlookMessageHeader dir=ltr> </DIV>
<DIV align=left class=OutlookMessageHeader dir=ltr>Best way to do
it is to get the initial results from DAO layer and cache them at the client
and use a simple Iterator pattern for page navigation. To optimize the
results
you can retrieve only the key elements from DAO and cache them at client
.
And you would do a complete query for only those set of records that are
to be displayed in the page.</DIV>
<DIV align=left class=OutlookMessageHeader dir=ltr> </DIV>
<DIV align=left class=OutlookMessageHeader dir=ltr>-Sridhar
Kancharlapalli.</DIV>
<DIV align=left class=OutlookMessageHeader dir=ltr> </DIV>
<DIV align=left class=OutlookMessageHeader dir=ltr> Hi all, Some questions
regarding the page by page iterator pattern. I learnt how this
patterns
works looking at the petstore application. Then I tried to search on google a
full description of this pattern, but I found only one document in
spanish. First question. Can anyone of you send me a link with
a
full description of this pattern? Second question. I
have
a DAO layer which perform a specific JDBC query Q that returns a set of data
of type T. Now I want display this result page by page. If I use the
Page by Page Iterator pattern, the query Q will be executed each time the
user
switch from a page to another (each time the start point of the cursor in
the Resultset will change). But this is not acceptable if the query is very
expansive. I read a thread on theserverside.com but I do not
understand
what to do in this case. I think that the Page by Page Iterator is not
appropriate in this case. Third Question. Is it possible
combine
the Page by Page solution with another pattern that is more appropriate for
complex queries? In this way the client know that the result is paged but
it do not know how this paging is implemented (Page by Page or other
patterns). Thanks in advance for any help.
====================================================================
Companion
Site: http://www.corej2eepatterns.com J2EE BluePrints:
http://java.sun.com/blueprints/corej2eepatterns List Archive:
http://archives.java.sun.com/archives/j2eepatterns-interest.html
Unsubscribing: email "signoff J2EEPATTERNS-INTEREST" to listserv@(protected)
</DIV></BLOCKQUOTE></BODY></HTML>
====================================================================
Companion Site: http://www.corej2eepatterns.com
J2EE BluePrints: http://java.sun.com/blueprints/corej2eepatterns
List Archive: http://archives.java.sun.com/archives/j2eepatterns-interest.html
Unsubscribing: email "signoff J2EEPATTERNS-INTEREST" to listserv@(protected)