The following comment has been added to this issue:
Author: fabrizio giustina
Created: Sat, 16 Oct 2004 5:44 AM
Body:
I tested james implementation, many details are not taken into account:
- the "export full list" doesn't work anymore, list is always splitted
- listIndex/viewIndex in tableDecorator are now wrong
- optimization is only done when the underlining object is a list, is there any way to
make it more generic (using commons-collections utils)?
Some more tests needed for:
- are offset/length attributes considered in smart paging?
- when offset is set, column body for rows < offset should not be executed
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View this comment:
http://jira.codehaus.org/browse/DISPL-14?page=comments#action_25463
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View the issue:
http://jira.codehaus.org/browse/DISPL-14
Here is an overview of the issue:
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Key: DISPL-14
Summary: Smart Paging
Type: Improvement
Status: Unassigned
Priority: Major
Original Estimate: Unknown
Time Spent: Unknown
Remaining: Unknown
Project: DisplayTag
Components:
Tag Library
Versions:
1.0 RC2
Assignee:
Reporter: fabrizio giustina
Created: Sat, 25 Sep 2004 4:39 AM
Updated: Sat, 16 Oct 2004 5:44 AM
Description:
====
imported from sf tracker
id 1026408
submitted by Ivan Markov - ivan_markov
http://sourceforge.net/tracker/index.php?func=detail&group_id=73068&atid=536613&aid=1026408
====
Smart Paging
------------
Smart paging refers to the ability of DT to deal with large lists of data. The problem
with the current DT approach is that:
a) The whole (potentially large) list of data has to be created for the DT tag,
occupying lots of memory.
b) If the list contains 1000s of records, populated with data from a SQL Server (99%
of the cases, I would say), you have huge network traffic between the webapp and the
server. Our code is especially useful for servers like Oracle & MySQL which have
built-in means to return only a subset of DB cursor's content.
There's one solution + one enhancement on the forums already (issue #1013526), so why
a third one?
We didn't like in the earlier proposal that it deals with intercepting DT's request
and parsing DT's request parameters, which seems a bit hacky. Also, we avoid the
complications of parsing parameters when there is > 1 table tag on the page. Not to
mention that the older proposal does not deal with full list sorting, or does it?
Instead, we introduced a new interface, DataProvider. It has two methods:
- List getData(int unsortedOffset, int unsortedLength, int recordOffset, int pageSize,
String sortedColumnName, boolean sortOrderAscending);
- int getDataCount();
The first two parameters unsortedOffset & unsortedLength are only needed for
supporting DT's setOffset()/setLength() features.
In our patch, DataProvider is used as a "callback" into user's code. The user is
supposed to implement the two methods of this interface.
The code in TableTag and its supporting classes is changed in a way that, for each
response where DT is rendered,
a) One call is issued to DataProvider.getDataCount(), which retrieves the total number
of rows in the data set (needed for DT to calculate the number of pages).
b) One call is issued to DataProvider.getData(), with the current page, page size &
sorting info.
A sample implementation of user-supplied JDBC DataProvider follows, in pseudocode.
Some JDBC exception handling stuff omitted.
<%
request.setAttribute("list", new DataProvider() {
List getData(int unsortedOffset, int unsortedLength, int recordOffset, int
pageSize, String sortedColumnName, boolean sortOrderAscending) {
Connection con = <app-specific way to get connection>;
PreparedStatement ps = con.prepareStatement("SELECT * FROM MyTable ORDER BY ?
LIMIT ?, ?"):
ps.setString(1, sortedColumnName);
ps.setInt(2, recordOffset);
ps.setInt(3, pageSize);
//etc..
ResultSet rs = con.execute();
return <app-specific way of getting List from ResultSet; Maybe use RowSet
instead of List?>;
}
int getDataCount() {
Connection con = <app-specific way to get connection>;
PreparedStatement ps = con.prepareStatement("SELECT count(*) FROM
MyTable"):
ResultSet rs = con.execute();
rs.next();
return rs.getInt(1);
}
});
%>
(DataProvider implementation code can be moved to Struts Controller/Action, depending
on the MVC framework used, in order not to polute the JSP code with Java scriptlets.)
Smart Paging Compatibility
--------------------------
We tried to change DT's code so that all older code to continue to work.
If user has provided an old-style List containing all the data, DT will automatically
wrap it with a ListDataProvider.
Current DT functionality (full-list sorting, decorations, multiple tables per page,
etc.) is supported, except for these two cases:
a) Full list(not page) sorting by a decorated column - sorting is done without
regarding the decorator.
b) Full list sorting by a column with no "property" attribute (static or implicit
object call via servlet) - no sorting is performed at all.
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