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<td><font size="+2"><b>contrib:FormTable</b></font></td>
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<tr>
<td>
<A href="../api/org/apache/tapestry/contrib/table/components/FormTable.html">org.apache.tapestry.contrib.table.components.FormTable</a>
</td>
</tr>
</table>
</td>
<td>
<table align="right" valign="middle" bgcolor="#c0c0c0" cellpadding="8">
<tr>
<td>Visual Component</td>
</tr>
</table>
</td>
</tr>
<tr valign="center">
<td colspan="2">&nbsp;</td>
</tr>
<tr>
<td colspan="2">
<b>Description</b>
<br>
A version of the <A HREF="contrib.Table.html"><CODE>Table</CODE></A> component
designed for use in a form. Like Table, this component allows you to present a sortable and pagable table
simply and easily. It also stores the items it dispays in hidden fields in the form,
so that they are identical during the rewind cycle when the form is submitted,
and generates links that submit the form, so that any other form information is preserved.
<p>
The differences between FormTable and Table are the following:
<ul>
<li> It uses TableFormRows instead of TableRows
which stores the rendered items in hidden form fields
<li> It uses TableFormPages instead of TablePages
which generates links that submit the form besides changing the page
<li> If the columns are defined using a string in the <code>columns</code> parameter,
it ensures that the headers of the generated columns contain links that also submit the form.
</ul>
<p>
The FormTable component allows you to manipulate its appearance by allowing you
to define the 'class' attributes of its internal elements. If you want to change
the structure of the table, however, you can instead build your own using the
lower level components
<A HREF="contrib.TableView.html"><CODE>TableView</CODE></A>,
<A HREF="contrib.TablePages.html"><CODE>TablePages</CODE></A>,
<A HREF="contrib.TableFormPages.html"><CODE>TableFormPages</CODE></A>,
<A HREF="contrib.TableColumns.html"><CODE>TableColumns</CODE></A>,
<A HREF="contrib.TableRows.html"><CODE>TableRows</CODE></A>,
<A HREF="contrib.TableFormRows.html"><CODE>TableFormRows</CODE></A>,
and
<A HREF="contrib.TableValues.html"><CODE>TableValues</CODE></A>.
<p>
The FormTable component delegates the handling of the table model and related
activities to the <A HREF="contrib.TableView.html"><CODE>TableView</CODE></A>,
and more detailed information about the process can be found in the
documentation of that class.
</td>
</tr>
<tr>
<td colspan="2">
<b>Providing the data</b>
<p>
There are many ways to provide the component with the data it has to render,
but here are the three major ones:
<ol>
<li> The data is passed to the <code>source</code> parameter in the form of an array,
a collection, or an iterator, and the table columns are defined using the
<code>columns</code> parameter (see further for details).
Both of these parameters will be evaluated at every request by default,
so changes in the data or the table columns will be displayed immediately.
<p>
This is the easiest and most straightforward approach. It has one performance limitation,
however - if the table is sorting the data according to a given column,
the sorting will be performed at every request.
The next methods provide ways to resolve this possible performance issue.
<p></p>
<li> The data is passed to the <code>source</code> parameter via an object that
implements the <A HREF="../api/org/apache/tapestry/contrib/table/model/IBasicTableModel.html"><CODE>IBasicTableModel</CODE></A>
interface. Through that interface you are given the sorting column (if any) and
the numbers of the items that will be displayed on the current page.
You then need to provide the component with the corresponding data.
<p>
This method allows you to perform the sorting in the database and load only the data
that will be displayed on the current page
(e.g. by using the ORDER BY, LIMIT, and OFFSET clauses in SQL)
and hence it could be far more efficient.
<p></p>
<li> All of the information (data, columns, state) is packaged in an
<A HREF="../api/org/apache/tapestry/contrib/table/model/ITableModel.html"><CODE>ITableModel</CODE></A>
and is passed to the <code>tableModel</code> parameter.
<p>
This approach allows greatest flexibility, but is recommended only for advanced users of the Table components.
</ol>
<p></p>
</td>
</tr>
<tr>
<td colspan="2">
<b>Defining the columns</b>
<p>
If you define the table columns using the <code>columns</code> parameter, you can either
provide a list of <A HREF="../api/org/apache/tapestry/contrib/table/model/ITableColumn.html"><code>ITableColumn</code></A>
objects, each defining a column in the table, or you can define the columns using
a string that describes each column.
<p>
The string describing the columns must be formatted in the following way:
<ul>
<li>The column definitions in the string are separated by commas
<p>
<li>Each column definition must be of one of the following types:<p>
<dl>
<dd>id</dd>
<dd>id:expression</dd>
<dd>id:description:expression</dd>
</dl>
<br>
Here the <b>id</b> defines the identification of the column, the <b>expression</b> is an
OGNL expression that extracts the column value from the row object, and <b>description</b>
is the title of the column if it is not defined otherwise.
<p>
Each column definition may be prefixed by the <b>!</b> character,
which identifies the column as non-sortable.
<p>
If defined, a Block with a name that is starts with the column id and
ends with <i>ColumnValue</i> will be used to render the column values.
Similarly, a Block with a name that starts with the column id and
ends with <i>ColumnHeader</i> will be used to render the column headers.
<p>
Finally, the title of the column will be taken from translation strings of the component
by using the column id as a key.
<p>
Please see the <SPAN class=code>LocaleSelection</SPAN> component for examples.
<p>
<li>A column definition may also be of the type
<p>
<dl>
<dd>=expression</dd>
</dl>
<br>
in which case it identifies an OGNL expression that returns an
<A HREF="../api/org/apache/tapestry/contrib/table/model/ITableColumn.html"><code>ITableColumn</code></A>
object defining the column.
<p>
<li>The full description string may be prefixed by the <b>*</b> character,
which means that the table is to be rendered within a form, and the
column headers must submit the form if they are clickable (i.e. if the column is sortable).
</ul>
<p>
Here is an example of the use of a description string to define columns:
<pre>
columns="locale:toString(), =currencyColumn, verbosity:Verbosity:currentRowVerbosity, !delete"
</pre>
<p></p>
</td>
</tr>
<tr>
<td colspan="2">
<b>See Also</b>
<br>
<A href="contrib.TableColumns.html">TableColumns</a>,
<A href="contrib.TablePages.html">TablePages</a>,
<A href="contrib.TableRows.html">TableRows</a>,
<A href="contrib.TableValues.html">TableValues</a>,
<A href="contrib.TableView.html">TableView</a>
</td>
</tr>
<tr>
<td colspan="2">
<b>Parameters</b>
<br>
<table border="1" cellpadding="4" cellspacing="4" class="parameters">
<tr>
<th>Name</th>
<th>Type</th>
<th>Direction</th>
<th>Required</th>
<th>Default</th>
<th>Description</th>
</tr>
<tr>
<td>source</td>
<td><code><A HREF="http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Object.html">Object</A>[]</code><br>
<code><A HREF="http://java.sun.com/j2se/1.4.2/docs/api/java/util/Collection.html">Collection</A></code><br>
<code><A HREF="http://java.sun.com/j2se/1.4.2/docs/api/java/util/Iterator.html">Iterator</A></code><br>
<A HREF="../api/org/apache/tapestry/contrib/table/model/IBasicTableModel.html"><CODE>IBasicTableModel</CODE></A>
</td>
<td>in</td>
<td rowspan="3">You must provide either both <code>source</code> and <code>columns</code> parameters
or the <code>tableModel</code> parameter</td>
<td>&nbsp;</td>
<td align="left">
The data to be displayed by the component. This parameter must be used
in combination with the <code>columns</code> parameter.
The parameter must be an array of values, a collection, an iterator,
or an object implementing the IBasicTableModel interface.
</td>
</tr>
<tr>
<td>columns</td>
<td>
<code><A HREF="http://java.sun.com/j2se/1.4.2/docs/api/java/lang/String.html">String</A></code><br>
<A HREF="../api/org/apache/tapestry/contrib/table/model/ITableColumnModel.html"><code>ITableColumnModel</code></A><br>
<A HREF="../api/org/apache/tapestry/contrib/table/model/ITableColumn.html"><code>ITableColumn[]</code></A><br>
<code><A HREF="http://java.sun.com/j2se/1.4.2/docs/api/java/util/List.html">List</A></code><br>
<code><A HREF="http://java.sun.com/j2se/1.4.2/docs/api/java/util/Iterator.html">Iterator</A></code>
</td>
<td>in</td>
<td>&nbsp;</td>
<td align="left">
The table columns to be displayed.
The parameter must be an array, a list, or an Iterator of ITableColumn objects,
an ITableColumnModel, or a String describing the columns (see documentation).
</td>
</tr>
<tr>
<td>tableModel</td>
<td><A HREF="../api/org/apache/tapestry/contrib/table/model/ITableModel.html"><CODE>ITableModel</CODE></A></td>
<td>in</td>
<td>&nbsp;</td>
<td align="left">The <A HREF="../api/org/apache/tapestry/contrib/table/model/ITableModel.html"><CODE>ITableModel</CODE></A> to be used to render the table.
The model contains all of the information needed to render the table and gives greatest flexibility,
but it may be harder to implement than simply using the <code>source</code> and <code>columns</code> parameters.
</td>
</tr>
<tr>
<td>tableSessionStateManager</td>
<td><A HREF="../api/org/apache/tapestry/contrib/table/model/ITableSessionStateManager.html"><CODE>ITableSessionStateManager</CODE></A></td>
<td>in</td>
<td>no</td>
<td>A custom session state manager that reloads the data at each request if it is provided
via the <code>source</code> and <code>columns</code> parameters or stores all
of it in the session if it is provided via the <code>tableModel</code> parameter</td>
<td align="left">This is the session state manager that will control what part of the
table model will be saved in the session state.
It is then used to recreate the table model by
using what was saved in the session.
<p> You can use one of the stock implementations of
<A HREF="../api/org/apache/tapestry/contrib/table/model/ITableSessionStateManager.html"><CODE>ITableSessionStateManager</CODE></A>
to determine the session state behaviour, or you can define your own.
</td>
</tr>
<tr>
<td>tableSessionStoreManager</td>
<td><A HREF="../api/org/apache/tapestry/contrib/table/model/ITableSessionStoreManager.html"><CODE>ITableSessionStoreManager</CODE></A></td>
<td>in</td>
<td>no</td>
<td>null</td>
<td align="left">Determines how the session state (returned by the session state manager)
will be saved in the session. If this parameter is null, then the state
will be saved as a persistent property. If it is not null, then the methods
of the interface will be used to save and load the state.
</td>
</tr>
<tr>
<td>convertor</td>
<td><A HREF="../api/org/apache/tapestry/contrib/table/model/IPrimaryKeyConvertor.html"><CODE>IPrimaryKeyConvertor</CODE></A></td>
<td>in</td>
<td>no</td>
<td>&nbsp;</td>
<td align="left">An interface defining how the items iterated upon by this component
will be stored in the form as Hidden values.
This interface allows only the primary key of the items to be stored, rather than
the whole item.</td>
</tr>
<tr>
<td>row</td>
<td>Object</td>
<td>out</td>
<td>no</td>
<td>&nbsp;</td>
<td align="left">The value object of the current row being rendered.</td>
</tr>
<tr>
<td>column</td>
<td><A HREF="../api/org/apache/tapestry/contrib/table/model/ITableColumn.html"><CODE>ITableColumn</CODE></A></td>
<td>out</td>
<td>no</td>
<td>&nbsp;</td>
<td align="left">The object representing the current column being rendered.</td>
</tr>
<tr>
<td>pageSize</td>
<td>
<code>int</code>
</td>
<td>in</td>
<td>no</td>
<td>10</td>
<td align="left">
The number of records displayed per page.
<p>
This parameter is only used with the <code>source</code> and <code>columns</code> parameters.
</td>
</tr>
<tr>
<td>initialSortColumn</td>
<td>
<code><A HREF="http://java.sun.com/j2se/1.4.2/docs/api/java/lang/String.html">String</A></code>
</td>
<td>in</td>
<td>no</td>
<td>null</td>
<td align="left">
The id of the column to initially sort the table by.
A value of <code>null</code> indicates no sorting.
<p>
This parameter is only used with the <code>source</code> and <code>columns</code> parameters.
</td>
</tr>
<tr>
<td>initialSortOrder</td>
<td>
<code>boolean</code>
</td>
<td>in</td>
<td>no</td>
<td>false</td>
<td align="left">
The order of the initial sorting.
Set this parameter to <code>false</code> to sort in an ascending order
and to <code>true</code> to sort in a descending one.
<p>
This parameter is only used with the <code>source</code> and <code>columns</code> parameters.
</td>
</tr>
<tr>
<td>pagesDisplayed</td>
<td>int</td>
<td>in</td>
<td>no</td>
<td>7</td>
<td align="left">Determines the maximum number of pages to be displayed in the page list
when the table has more than one page.
<p>For example, if the table has 20 pages, and 10 is the current page,
pages from 7 to 13 in the page list will be shown if this parameter has
a value of 7.
</td>
</tr>
<tr>
<td>arrowUpAsset</td>
<td><A HREF="../api/org/apache/tapestry/IAsset.html"><CODE>IAsset</CODE></A></td>
<td>in</td>
<td>no</td>
<td>&nbsp;</td>
<td align="left">The image to use to describe a column sorted in an ascending order.</td>
</tr>
<tr>
<td>arrowDownAsset</td>
<td><A HREF="../api/org/apache/tapestry/IAsset.html"><CODE>IAsset</CODE></A></td>
<td>in</td>
<td>no</td>
<td>&nbsp;</td>
<td align="left">The image to use to describe a column sorted in a descending order.</td>
</tr>
<tr>
<td>pagesClass</td>
<td>String</td>
<td>in</td>
<td>no</td>
<td>&nbsp;</td>
<td align="left">The CSS class of the table pages.</td>
</tr>
<tr>
<td>columnsClass</td>
<td>String</td>
<td>in</td>
<td>no</td>
<td>&nbsp;</td>
<td align="left">The CSS class of the table columns.</td>
</tr>
<tr>
<td>rowsClass</td>
<td>String</td>
<td>in</td>
<td>no</td>
<td>&nbsp;</td>
<td align="left">The CSS class of the table rows.</td>
</tr>
<tr>
<td>valuesClass</td>
<td>String</td>
<td>in</td>
<td>no</td>
<td>&nbsp;</td>
<td align="left">The CSS class of the table values.</td>
</tr>
</table>
<P>
Body: <STRONG>ignored</STRONG><BR>
Informal parameters: <STRONG>allowed</STRONG><br>
Reserved parameters: none
</P>
</td>
</tr>
<tr>
<td colspan="2">
<b>Examples</b>
<p>
You can find examples in the Tutorial
as part of the Workbench application under the "Table" tab.
<P>That page consists of two components -- the <SPAN
class=code>LocaleList</SPAN> component and the <SPAN
class=code>LocaleSelection</SPAN> component. </P>
<P>The <SPAN class=code>LocaleList</SPAN> component allows you to view all
Locales in a table (similar to the example above), as well as to choose Locales
from the table and add them to your "selection". </P>
<P>The <SPAN class=code>LocaleSelection</SPAN> component displays the selected
Locales and provides additional information about them. It also allows Locales
to be removed from the selection. </P>
<P>Even though the two components utilizing the Table are placed on a single
page, they can operate without any interference from each other with no effort
at all on part of the developer -- each table can be sorted independently, for
example. This is a good illustration of the power of Tapestry's component
approach. </P>
<p></p>
</td>
</tr>
<tr>
<td colspan="2">
<hr>
<H2>Table Internals Guide</H2>
This section is for advanced uses of the Table components only.
<P>
There are two important elements that comprise the Table
functionality -- the table model and the table components.
<P>The <STRONG>table model</STRONG> classes and interfaces provide the Table
with the ability to display and manipulate data from various different sources.
Using them in various combinations and customizing them allows the developer to
modify the behaviour of the table according to his needs. </P>
<P>The <STRONG>table components</STRONG> are responsible for displaying the data
provided by the table model, and working with them allows the developer to
radically change the appearance of the table if necessary. </P>
<H3>1. The Model </H3>
<P>This section will discuss the table model and how it can be used and modified
to satisfy the needs of the developer. The next section will then concentrate on
how the table components can be used to customize the appearance of the table as
much as possible. </P>
<H4>1.1. The Table Model Family of Classes </H4>Even though using a table model
can be very simple, as shown in the first example, behind the curtains it may
consist of many different interfaces and classes that work together to allow you
to modify different aspects of the table data representation and manipulation
without a lot of effort.
<P>Below you can see a UML Class diagram of the interfaces and classes in the
Table Model family. The rest of this section will discuss how they can be used
and modified as needed. </P>
<P><IMG alt="Table Model Class Diagram"
src="images/tableModel.gif"> </P>
<H4>1.2. The Table Model </H4>The table model provides the information needed by
the view to render the table. For example, the Table component may use its <SPAN
class=code>tableModel</SPAN> parameter to determine what to display.
<P>The Tapestry components access the table model via the relatively simple
<B><SPAN class=code>ITableModel</SPAN></B> interface, which is the facade of the
table model hierarchy. A variety of implementations of this interface can be
created to target different cases. </P>
<P>The contrib library currently defines only one rudimentary implementation
that can be used in the majority of situations -- the <B><SPAN
class=code>SimpleTableModel</SPAN></B>. While versatile, however, this
implementation may not be suitable for all cases, and hence you may create your
own whenever necessary. </P>
<P>Using the <SPAN class=code>SimpleTableModel</SPAN> is very easy -- you just
need to provide it with the data to be displayed and the columns that the table
will have: </P><PRE> Object[] data = ...;
ITableColumn[] columns = ...;
ITableModel model = new SimpleTableModel(data, columns);
</PRE>
<P>This model can then be passed to the Table component, and it will display the
data using the given columns. <BR></P>
<H4>1.3. The Data Model </H4>The <SPAN class=code>SimpleTableModel</SPAN> can
also obtain its data via the <SPAN class=code>ITableDataModel</SPAN> interface.
This allows the source of data to be abstracted.
<P>The contrib library provides two standard implementations of this interface.
The <SPAN class=code>SimpleListTableDataModel</SPAN> and the <SPAN
class=code>SimpleSetTableDataModel</SPAN>. As the names indicate, the former
provides the table data from Lists and arrays, while the latter provides the
data from Sets and other unordered Collections. Using the data models is very
simple as well: </P><PRE> ArrayList data = ...;
ITableDataModel dataModel = new SimpleListTableDataModel(data);
ITableModel model = new SimpleTableModel(dataModel, ...);
</PRE>
<P>An example of using <SPAN class=code>SimpleSetTableDataModel</SPAN> can be
found in the <SPAN class=code>LocaleSelection</SPAN> component in the Workbench.
The storage of the selected locales there is implemented precisely using that
table data model.</P>
<H4>1.4. The Column Model </H4>
<P>A column in the table model is defined using the <STRONG><SPAN
class=code>ITableColumn</SPAN></STRONG> interface. It provides the information
needed to identify the column (the column name), to render the column (the
columnRender that renders the heading, and the valueRenderer that renders each
cell), and to sort the column (whether the column is sortable and what <SPAN
class=code>Comparator</SPAN> should be used for sorting the table). </P>
<P>The basic implementation of <SPAN class=code>ITableColumn</SPAN> provided is
<STRONG><SPAN class=code>SimpleTableColumn</SPAN></STRONG>. It takes care of all
mundane tasks, such as supplying a renderer for the column header, and allows
you to define a column by only providing its name and a way to extract the
column data from the row object by overriding the <SPAN
class=code>getColumnValue()</SPAN> method. This is demonstrated by the example
below that also configures the column to be sortable: </P><PRE> // Create a new sortable column with name and title "Full Name"
ITableColumn fullNameColumn = new SimpleTableColumn("Full Name", true) {
public Object getColumnValue(Object value) {
PersonInfo info = (PersonInfo) value;
return info.getLastName() + ", " + info.getFirstName();
}
};
</PRE>
<P>Other methods can be overridden as well to provide additional features, such
as custom rendering, as it will be shown in the next section. </P>
<P>The above can be achieved in a simpler, but not as flexible manner by using
<SPAN class=code><STRONG>ExpressionTableColumn</STRONG></SPAN>. It inherits
<SPAN class=code>SimpleTableColumn</SPAN>, and allows you to create columns
whose data is obtained via OGNL: </P><PRE> // Create a new sortable column with name and title "Occupation"
ITableColumn occupationColumn = new ExpressionTableColumn("Occupation", "occupation", true);
// Create a new sortable column with name and title "Full Name"
ITableColumn fullNameColumn = new ExpressionTableColumn("Full Name", "lastName + \", \" + firstName", true);
</PRE>
<P>The table columns are supplied to the table model using a <SPAN
class=code>List</SPAN> -like container defined by the <SPAN
class=code><STRONG>ITableColumnModel</STRONG></SPAN> interface. The generic
implementation provided for this interface is<STRONG> <SPAN
class=code>SimpleTableColumnModel</SPAN></STRONG>, which contains an array of
<SPAN class=code>ITableColumn</SPAN> objects of any type. </P>
<P>One more specific implementation available is the<STRONG> <SPAN
class=code>ExpressionTableColumnModel</SPAN> </STRONG>, which contains<SPAN
class=code>ExpressionTableColumn</SPAN> objects. It allows you to define the
columns of your table quickly and easily, by providing a name and an OGNL
expression for each one in a <SPAN class=code>String</SPAN> array: </P><PRE> // Generate a simple sorting column model that uses OGNL to get the column data
ITableColumnModel objColumnModel =
new ExpressionTableColumnModel(new String[] {
"Locale", "toString()",
"Language", "language",
"Country", "country",
"Variant", "variant",
"ISO Language", "ISO3Language",
"ISO Country", "ISO3Country"
}, true);
</PRE>
<H4>1.5. The Table State </H4>
<P>The state of the table model consists of any data that is not related to the
contents of the table, but instead carries information about its presentation.
The standard table model supports two states -- the paging state (how many rows
per page; which page we are on) and the sorting state (which column we are
sorting on; in an ascending or a descending order). </P>
<P>The paging state is defined by the <STRONG><SPAN
class=code>ITablePagingState</SPAN></STRONG> interface and is implemented in its
simplest form by <STRONG><SPAN
class=code>SimpleTablePagingState</SPAN></STRONG>. Similarly, the sorting state
is defined by<STRONG> <SPAN class=code>ITableSortingState</SPAN> </STRONG>and is
implemented by<STRONG> <SPAN class=code>SimpleTableSortingState</SPAN></STRONG>.
</P>
<P>The states are typically accessed and modified by the components presenting
the table (e.g. the TablePages component can change the current page based on
the user selection). The user can also modify them, which is often necessary at
initialization: </P><PRE> ITableModel model = new SimpleTableModel(data, columns);
// Set page size to 15 elements and go to page 8
model.getPagingState().setPageSize(15);
model.getPagingState().setCurrentPage(8);
// Sort by column 'price' in an ascending order
model.getSortingState().setSortColumn("price", ITableSortingState.SORT_ASCENDING);
</PRE>
<P>The <SPAN class=code>SimpleTableModel</SPAN> &nbsp;class keeps the two states
together in the<STRONG> <SPAN class=code>SimpleTableState</SPAN>
</STRONG>object, which can be passed via the constructor and obtained at any
time using the <SPAN class=code>getState()</SPAN> method. This is often useful
when storing the state by itself is necessary (see below). </P>
<H4>1.6. The Session State Manager </H4>
<P>In Web interfaces, unlike client-side GUIs, the information about the state
of the presentation must be kept in the session object between requests. What
has to be kept and what can be thrown away and recreated during the next request
differs in each case, however. The policy of what to do typically involves a
tradeoff between memory and CPU power, and hence it depends very much on the
specific situation. </P>
<P>The<STRONG> <SPAN class=code>ITableSessionStateManager</SPAN>
</STRONG>interface is used to define precisely this policy. It defines what part
of the table model has to be saved in the session and can recreate the table
model using the saved information when the next request comes. </P>
<P>The <SPAN class=code>Table</SPAN> and the <SPAN class=code>TableView</SPAN>
components have a <SPAN class=code>tableSessionStateManager</SPAN> binding that
allows such a manager to be supplied. When the table model is needed at the
beginning of a new request, the component use the following procedure to obtain
it: </P>
<OL>
<LI>Load the session state (it will be null initially)
<LI>Invoke <SPAN class=code>recreateTableModel(sessionState)</SPAN> on the
Session State Manager to try to recrate the table model
<LI>If <SPAN class=code>recreateTableMode()</SPAN> returns null, use the <SPAN
class=code>tableModel</SPAN> binding to obtain the table model </LI></OL>
<P>Immediately before rendering, the opposite procedure takes place: </P>
<OL>
<LI>Invoke <SPAN class=code>getSessionState(tableModel)</SPAN> on the Session
State Manager to extract the part of the model to be saved
<LI>Save the session state </LI></OL>
<P>Three standard implementations of the <SPAN
class=code>ITableSessionStateManager</SPAN> interface are provided that address
the common cases that can be implemented without custom code. Each of them
implements a different policy for extracting session state from the model and
hence is suitable for some specific situations: </P>
<TABLE border=1 cellPadding=5 cellSpacing=0 width="100%">
<TBODY>
<TR>
<TH>Session State Manager </TH>
<TH>Description </TH></TR>
<TR>
<TD vAlign=center>
<P align=center><STRONG><SPAN
class=code>FullTableSessionStateManager</SPAN> </STRONG></P></TD>
<TD>
<P><STRONG>Saves the entire table model in the session. This is the
default manager.</STRONG> </P>
<P>This manager is the simplest to use as it brings to a minimum the need
for additional coding. It has a number of disadvantages, however. First,
everything in the table model must be <SPAN class=code>Serializable</SPAN>
since it is stored in the session and may be serialized at one point or
another. Second, depending on the table data, its memory consumption per
session could be quite significant. </P>
<P>For those reasons, it is probably not a good idea to use this manager
if you are displaying large amounts of data, if you have a lot of users,
or if the application needs to be clustered. On the other hand, it is
perfect for quick and dirty work. </P></TD></TR>
<TR>
<TD vAlign=center>
<P align=center><STRONG><SPAN
class=code>SimpleTableSessionStateManager</SPAN> </STRONG></P></TD>
<TD>
<P><STRONG>Saves only the table model state and assumes that the data and
column models are constant.</STRONG> </P>
<P>This manager is designed to work with the <SPAN
class=code>SimpleTableModel</SPAN> . It stores only the model state
(paging and sorting), and recreates the model using the data and column
models that must be supplied via its constructor. As a result, the session
memory consumption is low, but the CPU utilization may be high, since the
data must be resorted at each request. This manager is best used when the
data that needs to be displayed is constant. </P>
<P>An example of the use of the manager can be seen in the <SPAN
class=code>LocaleList</SPAN> component in the Workbench. That component
displays all locales available to the JVM -- information that does not
change and is too much to be stored in the session. </P></TD></TR>
<TR>
<TD vAlign=center>
<P align=center><STRONG><SPAN
class=code>NullTableSessionStateManager</SPAN> </STRONG></P></TD>
<TD>
<P><STRONG>Saves nothing at all and forces the component to always load
the table model from the <SPAN class=code>tableModel</SPAN>
binding.</STRONG> </P>
<P>This manager is typically used when the storing and creation of the
table model needs to be delegated to the parent component.
</P></TD></TR></TBODY></TABLE>
<P>One approach that is a good compromise between memory consumption and CPU
load is to store in the session only the state and the IDs of the objects in the
table. In this way CPU is not loaded, since re-sorting is no longer necessary,
and the memory consumption is not excessive, since the IDs tend not to take a
lot of space. Implementing this approach, however, requires a custom manager,
and possibly a custom <SPAN class=code>TableModel</SPAN> to limit the data
loaded from the database only to the elements that will be displayed on the
current page.</P>
<H4>1.7. The Session Store Manager </H4>
<P>While the Session State Manager determines <EM>what</EM> to store in the
session, the Session Store Manager determines <EM>how</EM> to store data in the
session. Normally the information that needs to be saved is stored using the
Tapestry persistent property mechanism. If a Session Store Manager is provided,
however, it is asked to take care of storing and loading of that information.
</P>
<P>This is typically necessary in two specific cases: </P>
<OL>
<LI>When the same table needs to be displayed on multiple pages. In that case
the persistent property method will not work as desired, and the table state
must be saved in the <SPAN class=code>Visit</SPAN> instead.
<LI>When the table is a part of a <SPAN class=code>Block</SPAN>, and the <SPAN
class=code>Block</SPAN> is used on more than one page. In that case the tables
displayed may be different, but a persistent page property will save their
states at the same location.&nbsp;Hence a custom Session Store Manager is
necessary. </LI></OL>
<P></P>
<P>The Session Store Managers implement the <STRONG><SPAN
class=code>ITableSessionStoreManager</SPAN></STRONG> interface. There are no
default implementations of this interface -- the developer must supply his own.
</P>
<P> </P>
<P></P>
<H3>2. Changing appearance </H3>
<P>While the table model defines what data should be displayed in the table, it
does not define how that data would look. The appearance is an important element
of the web applications, however, and so the table components provide a number
of ways to the developer to customize their looks. </P>
<H4>2.1. Setting styles </H4>
<P>The simplest way to modify how the table looks is by using CSS. The <SPAN
class=code>Table</SPAN> component provides a number of bindings allowing you to
set the CSS class of all major elements of the table. Please have a look at
<SPAN class=code>Table</SPAN>'s JavaDoc for details. </P>
<P>One interesting use of this approach is to define an <SPAN
class=code>evenOdd</SPAN> bean of type <SPAN
class=code>org.apache.tapestry.bean.EvenOdd</SPAN> and bind the rowsClass parameter
of table to <SPAN class=code>"beans.evenOdd.next"</SPAN>. In this way odd rows
in the table will receive the class "odd", and even rows will receive the class
"even", which allows for different formatting of neighbouring rows. </P>
<H4>2.2. Changing layout </H4>
<P>The <SPAN class=code>Table</SPAN> component is very easy to use, but it may
become a "straight jacket" if a different layout of the table is required. In
such a case, instead of <SPAN class=code>Table</SPAN>, the developer could use
the lower level table components described below: </P>
<TABLE border=1 cellPadding=5 cellSpacing=0>
<TBODY>
<TR>
<TH>Component</TH>
<TH>Wrapped by</TH>
<TH>Description</TH></TR>
<TR>
<TD align=middle><STRONG><SPAN class=code>TableView</SPAN></STRONG></TD>
<TD>&nbsp;</TD>
<TD>Wraps the whole table structure and manages the table model</TD></TR>
<TR>
<TD align=middle><STRONG><SPAN class=code>TablePages</SPAN></STRONG></TD>
<TD align=middle><SPAN class=code>TableView</SPAN></TD>
<TD>Displays the page navigation interface</TD></TR>
<TR>
<TD align=middle><STRONG><SPAN class=code>TableColumns</SPAN></STRONG></TD>
<TD align=middle><SPAN class=code>TableView</SPAN></TD>
<TD>Generates the column headers</TD></TR>
<TR>
<TD align=middle><STRONG><SPAN class=code>TableRows</SPAN></STRONG></TD>
<TD align=middle><SPAN class=code>TableView</SPAN></TD>
<TD>Enumerates all rows on the current page</TD></TR>
<TR>
<TD align=middle><STRONG><SPAN class=code>TableValues</SPAN></STRONG></TD>
<TD align=middle><SPAN class=code>TableRows</SPAN></TD>
<TD>Renders the values for each column of the current
row</TD></TR></TBODY></TABLE>
<P>&nbsp;The <SPAN class=code>Table</SPAN> component itself is based on those
components. Here is its template: </P><PRE> &lt;span jwcid="tableView"&gt;
&lt;span jwcid="condPages"&gt;&lt;span jwcid="tablePages"/&gt;&lt;/span&gt;
&lt;tr&gt;&lt;span jwcid="tableColumns"/&gt;&lt;/tr&gt;
&lt;tr jwcid="tableRows"&gt;&lt;td jwcid="tableValues"/&gt;&lt;/tr&gt;
&lt;/span&gt;
</PRE>
<P>You can use those components in a similar way to create a layout that you
want. You can change the location of the page navigation section, add other
columns in the table manually, or insert custom formatting. You can even build
your own components to replace some of the standard ones.</P>
<P>A good example of this approach is the <SPAN class=code>LocaleList</SPAN>
component in the Workbench. It modifies the layout slightly and adds a separate
column in the table that is not defined the table model.</P>
<H4>2.3. Changing renderers </H4>
<P>Another way to change the appearance of the table is by using the <SPAN
class=code>ITableColumn</SPAN> ability to provide custom renderers for both
column headers and values. By default, <SPAN class=code>SimpleTableColumn</SPAN>
uses <SPAN class=code>RenderString</SPAN> to display values and the <SPAN
class=code>SimpleTableColumnComponent</SPAN> to render the headers. That
component makes the header a link if the column is sortable, handles clicks on
it, and displays an indicator if the column is currently used for sorting. </P>
<P>If is quite possible to use custom components to render the values or the
headers in a different way. This is the approach taken by the <SPAN
class=code>LocaleSelection</SPAN> component in the Workbench. It uses Block
sections in its template to render some columns differently (see the demo). </P>
<P>While using this mechanism is not hard at all, there are a number of common
pitfalls that the developer must avoid. If you would like to go that route,
please see how the <SPAN class=code>SimpleTableColumnComponent</SPAN> and the
<SPAN class=code>LocaleSelection</SPAN> component are implemented and read the
JavaDocs of <SPAN class=code>org.apache.tapestry.components.BlockRenderer</SPAN> and
<SPAN class=code>org.apache.tapestry.ComponentAddress</SPAN> beforehand.</P>
<P>&nbsp;</P>
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