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http://jira.codehaus.org/browse/DISPL-14?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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[EMAIL PROTECTED] deleted DISPL-14:
-----------------------------------
> Smart Paging
> ------------
>
> Key: DISPL-14
> URL: http://jira.codehaus.org/browse/DISPL-14
> Project: DisplayTag
> Issue Type: Improvement
> Reporter: fabrizio giustina
> Assignee: fabrizio giustina
>
> ====
> 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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