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From tapestry-...@jakarta.apache.org
Subject [Jakarta Tapestry Wiki] Updated: MoreFrequentlyAskedQuestions
Date Thu, 18 Nov 2004 03:12:30 GMT
   Date: 2004-11-17T19:12:30
   Editor: JohnStudarus <john@jhlconsulting.com>
   Wiki: Jakarta Tapestry Wiki
   Page: MoreFrequentlyAskedQuestions
   URL: http://wiki.apache.org/jakarta-tapestry/MoreFrequentlyAskedQuestions

   no comment

Change Log:

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-
-<p class=MsoToc3 style='tab-stops:right dotted 431.5pt'><span
-class=MsoHyperlink><a href="#_Toc88480229">How do I pass information from page
-to page?</a></span><o:p></o:p></p>
-
-<p class=MsoToc3 style='tab-stops:right dotted 431.5pt'><span
-class=MsoHyperlink><a href="#_Toc88480230">I just created a new page and now I
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-
-<p class=MsoToc3 style='tab-stops:right dotted 431.5pt'><span
-class=MsoHyperlink><a href="#_Toc88480231">How can I share data across two
-Tapestry applications?</a></span><o:p></o:p></p>
-
-<p class=MsoToc3 style='tab-stops:right dotted 431.5pt'><span
-class=MsoHyperlink><a href="#_Toc88480232">What is Spindle?</a></span><o:p></o:p></p>
-
-<p class=MsoToc3 style='tab-stops:right dotted 431.5pt'><span
-class=MsoHyperlink><a href="#_Toc88480233">What are the jwcid=$content$ tags
-that Spindle places into my HTML files?</a></span><o:p></o:p></p>
-
-<p class=MsoToc3 style='tab-stops:right dotted 431.5pt'><span
-class=MsoHyperlink><a href="#_Toc88480234">When would I use the $remove$ tag?</a></span><o:p></o:p></p>
-
-<p class=MsoToc3 style='tab-stops:right dotted 431.5pt'><span
-class=MsoHyperlink><a href="#_Toc88480235">Why is my Visit object always null
-or throws NoClassDefFound?</a></span><o:p></o:p></p>
-
-<p class=MsoToc3 style='tab-stops:right dotted 431.5pt'><span
-class=MsoHyperlink><a href="#_Toc88480236">How do I make a property in a
-Component persistent?</a></span><o:p></o:p></p>
-
-<p class=MsoNormal><!--[if supportFields]><span style='mso-element:field-end'></span><![endif]--><![if
!supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<h3><a name="_Toc88480213"></a><a name="_Toc88480225"><span style='mso-bookmark:
-_Toc88480213'>Where is the (some random HTML) component? (i.e. TD)</span></a></h3>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<p class=MsoNormal>Any component that does not have a direct Tapestry component
-can be represented with the Tapestry ANY component.<span style="mso-spacerun:
-yes">  </span>For example, say you want to have Tapestry generate the
-background color for your table using a TD component you could use &lt;td
-jwcid=”@Any” bgcolor=”ognl:backgroundColor”&gt;&lt;/td&gt;.</p>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<h3><a name="_Toc88480214"></a><a name="_Toc88480226"><span style='mso-bookmark:
-_Toc88480214'>Why isn’t Initialize setting my variables when the page is
-created?</span></a> </h3>
-
-<p class=MsoNormal>Don’t worry; you aren’t the first person to make this
-mistake.<span style="mso-spacerun: yes">  </span>Initialize isn’t called when
a
-page is created – it is called when a page is returned to the pool to be
-reused.<span style="mso-spacerun: yes">  </span>Initialize is not to be used
to
-setup a page but instead return it to a pristine state so it can be recycled in
-the pool of available pages.<span style="mso-spacerun: yes">  </span>See the
-pageRenderListener interface if you want to setup state before a page is used.</p>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<h3><a name="_Toc88480215"></a><a name="_Toc88480227"><span style='mso-bookmark:
-_Toc88480215'>Where do I “initialize” values for a page?</span></a></h3>
-
-<p class=MsoNormal>You’ll probably want to use the pageRenderListener class to
-perform any work you need when the page is accessed.<span style="mso-spacerun:
-yes">  </span>Alternatively you can do some lazy initialization where objects
-are created the first time they are used.<span style="mso-spacerun: yes"> 
-</span>This isn’t as clean as using Tapestry properties but it should
-work.<span style="mso-spacerun: yes">  </span>For example:</p>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<p class=MsoNormal>AppointmentPage:</p>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<p class=MsoNormal>Protected Date date = null;</p>
-
-<p class=MsoNormal>Public Date getEvent() {</p>
-
-<p class=MsoNormal><span style="mso-spacerun: yes">  </span>if ( null
== date )
-{</p>
-
-<p class=MsoNormal><span style="mso-spacerun: yes">    </span>date =
new
-Date();</p>
-
-<p class=MsoNormal><span style="mso-spacerun: yes">  </span>}</p>
-
-<p class=MsoNormal><span style="mso-spacerun: yes">  </span>return date;</p>
-
-<p class=MsoNormal>}</p>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<h3><a name="_Toc88480216"></a><a name="_Toc88480228"><span style='mso-bookmark:
-_Toc88480216'>How do I use the pageRenderListener to setup my page before it is
-used?</span></a></h3>
-
-<p class=MsoNormal>Simply implement the PageRenderListener interface and
-override the pageBeginRender() routine.<span style="mso-spacerun: yes"> 
-</span>Often times you can just call initialize() from pageBeginRender() to
-setup the page – your logic in both routines may be the same.</p>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<p class=MsoNormal>public abstract class AppointmentPage extends BasePage
-implements PageRenderListener {</p>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<p class=MsoNormal>private Date date;</p>
-
-<p class=MsoNormal>// this is called by Tapestry when the page is called up</p>
-
-<p class=MsoNormal>public void pageBeginRender(PageEvent event) {</p>
-
-<p class=MsoNormal><span style='mso-tab-count:1'>            </span>//
do all
-your pre page processing here</p>
-
-<p class=MsoNormal><span style='mso-tab-count:1'>            </span>date
= new
-Date();</p>
-
-<p class=MsoNormal>}</p>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<p class=MsoNormal>// this is called by Tapestry before it is return to the
-pool for reuse</p>
-
-<p class=MsoNormal>public void initialize() {</p>
-
-<p class=MsoNormal><span style='mso-tab-count:1'>            </span>date
= new
-Date();</p>
-
-<p class=MsoNormal>}</p>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<h3><a name="_Toc88480217"></a><a name="_Toc88480229"><span style='mso-bookmark:
-_Toc88480217'>How do I pass information from page to page?</span></a></h3>
-
-<p class=MsoNormal>You can use a Visit object to keep state from page to page
-but this is probably overkill and cumbersome if you just want to pass some
-information from one page to the next.<span style="mso-spacerun: yes"> 
-</span>Instead you will want to create an instance of the next page, pass the
-parameter and then call (activate) the next page.<span style="mso-spacerun:
-yes">  </span>Here is some sample code:</p>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<p class=MsoNormal>Calling Page Java:</p>
-
-<p class=MsoNormal>public void submitAction(IRequestCycle cycle) {</p>
-
-<p class=MsoNormal>&nbsp; // The next page we want to go to is the Result page</p>
-
-<p class=MsoNormal><span style="mso-spacerun: yes">  </span>AppointmentPage
-next_page = (AppointmentPage)cycle.getPage(&quot;Appointment&quot;);<br>
-&nbsp; next_page.setDate(new Date());</p>
-
-<p class=MsoNormal><span style="mso-spacerun: yes"> 
-</span>next_page.setEvent(“Birthday Party”);</p>
-
-<p class=MsoNormal><span style="mso-spacerun: yes"> 
-</span>cycle.activate(next_page);</p>
-
-<p class=MsoNormal>}</p>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<p class=MsoNormal>Appointment Page:</p>
-
-<p class=MsoNormal>&lt;property-specification name=&quot;date&quot;
-type=&quot;java.lang.Date&quot; persistent=&quot;yes&quot;/&gt;</p>
-
-<p class=MsoNormal>&lt;property-specification name=&quot;event&quot;
-type=&quot;java.lang.String&quot; persistent=&quot;yes&quot;/&gt;</p>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<p class=MsoNormal>Appointment Page Java:</p>
-
-<p class=MsoNormal>public void setDate(Date date);</p>
-
-<p class=MsoNormal>public void setEvent(String event); </p>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<h3><a name="_Toc88480218"></a><a name="_Toc88480230"><span style='mso-bookmark:
-_Toc88480218'>I just created a new page and now I get a 'class instantiation
-problem'.<span style="mso-spacerun: yes">  </span>Why can’t it instantiate
my
-class?</span></a></h3>
-
-<p class=MsoNormal>Most likely you created your class abstract when it didn’t
-need to be.<span style="mso-spacerun: yes">  </span>Tapestry doesn’t create
an
-enhanced subclass if there are no <span style='font-size:11.0pt;font-family:
-Arial;color:black'>&lt;property-specification&gt; elements.<span
-style="mso-spacerun: yes">  </span>A concrete class is never created by
-Tapestry in this case and since abstract classes cannot be instantiated, this
-exception pops up.<span style="mso-spacerun: yes">  </span>You either need to
-create a &lt;property-specification&gt; element or make your class concrete by
-removing the abstract identifier.<o:p></o:p></span></p>
-
-<p class=MsoNormal><span style='font-size:11.0pt;font-family:Arial;color:black'><![if
!supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></span></p>
-
-<h3><a name="_Toc88480219"></a><a name="_Toc88480231"><span style='mso-bookmark:
-_Toc88480219'>How can I share data across two Tapestry applications?</span></a></h3>
-
-<p class=MsoNormal>Even if you’re running two Tapestry applications within the
-same Application Server (i.e. Tomcat) you can’t share data between them within
-the Application Server.<span style="mso-spacerun: yes">  </span>You can merge
-the two applications together into one application and then share data through
-singleton objects within the Application Server.<span style="mso-spacerun:
-yes">  </span>Alternatively the two applications can share data at a lower
-level common level, i.e. the operating system (message passing) or a database.</p>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<h3><a name="_Toc88480220"></a><a name="_Toc88480232"><span style='mso-bookmark:
-_Toc88480220'>What is Spindle?</span></a></h3>
-
-<p class=MsoNormal>Spindle is a plugin for the Eclipse IDE.<span
-style="mso-spacerun: yes">  </span>Eclipse is available at <a
-href="http://www.eclipse.org/">www.eclipse.org</a> and Spindle is available at
-spindle.sourceforge.net.<span style="mso-spacerun: yes">  </span>The Spindle
-adds intelligence about Tapestry into Eclipse.<span style="mso-spacerun: yes"> 
-</span>The end result is an IDE that is aware of Tapestry Components and Pages
-by providing Wizard interfaces and navigation widgets for the creation and
-viewing of Tapestry Components and Pages.<span style="mso-spacerun: yes"> 
-</span>It is well worth a look if you intend on developing with Tapestry.<span
-style="mso-spacerun: yes">  </span>Download Eclipse first and then install
-Spindle through the auto update feature of Eclipse.</p>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<h3><a name="_Toc88480221"></a><a name="_Toc88480233"><span style='mso-bookmark:
-_Toc88480221'>What are the jwcid=$content$ tags that Spindle places into my
-HTML files?</span></a></h3>
-
-<p class=MsoNormal>Tapestry does not process any text outside of a &lt;span
-jwcid=”$content$”&gt;&lt;/span&gt;.<span style="mso-spacerun: yes"> 
-</span>This allows a developer to place documentation, header files or static
-HTML (that should not be rendered by the Tapestry engine).<span
-style="mso-spacerun: yes">  </span>Spindle places these tags into the HTML out
-of convenience.<span style="mso-spacerun: yes">  </span>The can be deleted
-without any problems.</p>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<h3><a name="_Toc88480222"></a><a name="_Toc88480234"><span style='mso-bookmark:
-_Toc88480222'>When would I use the $remove$ tag?</span></a></h3>
-
-<p class=MsoNormal>The $remove$ tag is used as an aid to view static HTML
-pages.<span style="mso-spacerun: yes">  </span>The Tapestry Engine removes the
-tag and any text insert within when the page is rendered.<span
-style="mso-spacerun: yes">  </span>This is useful when the text would otherwise
-be generated dynamically and an HTML designer needs to mock up the pages
-statically.<span style="mso-spacerun: yes">  </span>In the following example,
-three lines would be displayed when the page is statically viewed while the
-Tapestry Engine would render the one line dynamically when it is iterated
-through the Foreach component.</p>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<p class=MsoNormal>&lt;table&gt;</p>
-
-<p class=MsoNormal>&lt;tr jwcid=”employeeForeach”&gt;</p>
-
-<p class=MsoNormal><span style="mso-spacerun: yes">  </span>&lt;td&gt;&lt;span
-jwcid=”employeeName”&gt;Jane&lt;/span&gt;&lt;/td&gt;</p>
-
-<p class=MsoNormal><span style="mso-spacerun: yes">  </span>&lt;span
-jwcid=”$remove$”&gt;</p>
-
-<p class=MsoNormal><span style="mso-spacerun: yes"> 
-</span>&lt;td&gt;Sally&lt;/td&gt;</p>
-
-<p class=MsoNormal><span style="mso-spacerun: yes"> 
-</span>&lt;td&gt;Sue&lt;/td&gt;</p>
-
-<p class=MsoNormal><span style="mso-spacerun: yes">  </span>&lt;span/&gt;</p>
-
-<p class=MsoNormal>&lt;/tr&gt;</p>
-
-<p class=MsoNormal>&lt;/table&gt;</p>
-
-<p class=MsoNormal><span style="mso-spacerun: yes"> </span></p>
-
-<h3><a name="_Toc88480223"></a><a name="_Toc88480235"><span style='mso-bookmark:
-_Toc88480223'>Why is my Visit object always null or throws NoClassDefFound?</span></a></h3>
-
-<p class=MsoNormal>You might want to check that your Visit class is defined in
-the application specification.<span style="mso-spacerun: yes">  </span>If it
is
-not defined you will run into problems when calling page.getVisit().<span
-style="mso-spacerun: yes">  </span>Make sure you put a fully qualified class
-name in the property.</p>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<p class=MsoNormal>MyApp.application:</p>
-
-<p class=MsoNormal>&lt;property
-name=&quot;org.apache.tapestry.visit-class&quot; value=&quot;some.example.Visit&quot;
-/&gt;</p>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<p class=MsoNormal>AppointmentPage.java:</p>
-
-<p class=MsoNormal>Public void submit() {</p>
-
-<p class=MsoNormal><span style='mso-tab-count:1'>            </span>//
-getVisit() will need to be casted to the defined Visit class</p>
-
-<p class=MsoNormal><span style='mso-tab-count:1'>            </span>Some.example.Visit
-visit = (Some.example.Visit)getPage().getVisit();</p>
-
-<p class=MsoNormal>}</p>
-
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
-
-<h3><a name="_Toc88480224"></a><a name="_Toc88480236"><span style='mso-bookmark:
-_Toc88480224'>How do I make a property in a Component persistent?</span></a></h3>
-
-<p class=MsoNormal>Pages support persistent properties so place the persistent
-property in the encompassing Page and pass it into the Component.<span
-style="mso-spacerun: yes">  </span>The property will remain persistent and be
-passed into the Component as a parameter.<span style="mso-spacerun: yes"> 
-</span>The Component will need not know, or care, that the property is
-persistent.</p>
+== Where is the (some random HTML) component? (i.e. TD) ==
+Any component that does not have a direct Tapestry component can be represented with the
Tapestry ANY component.  For example, say you want to have Tapestry generate the background
color for your table using a TD component you could use <td jwcid=”@Any” bgcolor=”ognl:backgroundColor”></td>.
 
-<p class=MsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></p>
+== Why isn’t Initialize setting my variables when the page is created? ==
+
+Don’t worry; you aren’t the first person to make this mistake.  Initialize isn’t called
when a page is created – it is called when a page is returned to the pool to be reused. 
Initialize is not to be used to setup a page but instead return it to a pristine state so
it can be recycled in the pool of available pages.  See the pageRenderListener interface if
you want to setup state before a page is used.
+
+== Where do I “initialize” values for a page? ==
+
+You’ll probably want to use the pageRenderListener class to perform any work you need when
the page is accessed.  Alternatively you can do some lazy initialization where objects are
created the first time they are used.  This isn’t as clean as using Tapestry properties but
it should work.  For example:
+
+AppointmentPage:
+
+Protected Date date = null;
+Public Date getEvent() {
+  if ( null == date ) {
+    date = new Date();
+  }
+  return date;
+}
+
+== How do I use the pageRenderListener to setup my page before it is used? ==
+
+Simply implement the PageRenderListener interface and override the pageBeginRender() routine.
 Often times you can just call initialize() from pageBeginRender() to setup the page – your
logic in both routines may be the same.
+
+public abstract class AppointmentPage extends BasePage implements PageRenderListener {
+
+private Date date;
+// this is called by Tapestry when the page is called up
+public void pageBeginRender(PageEvent event) {
+	// do all your pre page processing here
+	date = new Date();
+}
+
+// this is called by Tapestry before it is return to the pool for reuse
+public void initialize() {
+	date = new Date();
+}
+
+== How do I pass information from page to page? ==
+
+You can use a Visit object to keep state from page to page but this is probably overkill
and cumbersome if you just want to pass some information from one page to the next.  Instead
you will want to create an instance of the next page, pass the parameter and then call (activate)
the next page.  Here is some sample code:
+
+Calling Page Java:
+public void submitAction(IRequestCycle cycle) {
+  // The next page we want to go to is the Result page
+  AppointmentPage next_page = (AppointmentPage)cycle.getPage("Appointment");
+  next_page.setDate(new Date());
+  next_page.setEvent(“Birthday Party”);
+  cycle.activate(next_page);
+}
+
+Appointment Page:
+<property-specification name="date" type="java.lang.Date" persistent="yes"/>
+<property-specification name="event" type="java.lang.String" persistent="yes"/>
+
+Appointment Page Java:
+public void setDate(Date date);
+public void setEvent(String event); 
+
+== I just created a new page and now I get a 'class instantiation problem'.  Why can’t it
instantiate my class? ==
+
+Most likely you created your class abstract when it didn’t need to be.  Tapestry doesn’t
create an enhanced subclass if there are no <property-specification> elements.  A concrete
class is never created by Tapestry in this case and since abstract classes cannot be instantiated,
this exception pops up.  You either need to create a <property-specification> element
or make your class concrete by removing the abstract identifier.
+
+== How can I share data across two Tapestry applications? ==
+
+Even if you’re running two Tapestry applications within the same Application Server (i.e.
Tomcat) you can’t share data between them within the Application Server.  You can merge the
two applications together into one application and then share data through singleton objects
within the Application Server.  Alternatively the two applications can share data at a lower
level common level, i.e. the operating system (message passing) or a database.
+
+== What is Spindle? ==
+
+Spindle is a plugin for the Eclipse IDE.  Eclipse is available at www.eclipse.org and Spindle
is available at spindle.sourceforge.net.  The Spindle adds intelligence about Tapestry into
Eclipse.  The end result is an IDE that is aware of Tapestry Components and Pages by providing
Wizard interfaces and navigation widgets for the creation and viewing of Tapestry Components
and Pages.  It is well worth a look if you intend on developing with Tapestry.  Download Eclipse
first and then install Spindle through the auto update feature of Eclipse.
+
+== What are the jwcid=$content$ tags that Spindle places into my HTML files? ==
+
+Tapestry does not process any text outside of a <span jwcid=”$content$”></span>.
 This allows a developer to place documentation, header files or static HTML (that should
not be rendered by the Tapestry engine).  Spindle places these tags into the HTML out of convenience.
 The can be deleted without any problems.
+
+== When would I use the $remove$ tag? ==
+
+The $remove$ tag is used as an aid to view static HTML pages.  The Tapestry Engine removes
the tag and any text insert within when the page is rendered.  This is useful when the text
would otherwise be generated dynamically and an HTML designer needs to mock up the pages statically.
 In the following example, three lines would be displayed when the page is statically viewed
while the Tapestry Engine would render the one line dynamically when it is iterated through
the Foreach component.
+
+<table>
+<tr jwcid=”employeeForeach”>
+  <td><span jwcid=”employeeName”>Jane</span></td>
+  <span jwcid=”$remove$”>
+  <td>Sally</td>
+  <td>Sue</td>
+  <span/>
+</tr>
+</table>
+
+== Why is my Visit object always null or throws NoClassDefFound? ==
+
+You might want to check that your Visit class is defined in the application specification.
 If it is not defined you will run into problems when calling page.getVisit().  Make sure
you put a fully qualified class name in the property.
+
+MyApp.application:
+<property name="org.apache.tapestry.visit-class" value="some.example.Visit" />
+
+AppointmentPage.java:
+Public void submit() {
+	// getVisit() will need to be casted to the defined Visit class
+	Some.example.Visit visit = (Some.example.Visit)getPage().getVisit();
+}
+
+== How do I make a property in a Component persistent? ==
+
+Pages support persistent properties so place the persistent property in the encompassing
Page and pass it into the Component.  The property will remain persistent and be passed into
the Component as a parameter.  The Component will need not know, or care, that the property
is persistent.
 
-</div>

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