Source Viewer : /general/exception.htm

This page demonstrates Clicks error handling.

<dl>
   
<dt><a href="${nullPointerLink.href}">NullPointerException</a></dt>
<dd>
This error is caused by the Pages <tt>onExceptionClick()</tt> method throwing a 
<tt>NullPointerException</tt>. Note how the error report shows you the exact line
where the error occurred. Click will do this if it can find the Java source code 
on the classpath or under the WEB-INF directory.
</dd>

<dt><a href="${illegalArgumentLink.href}">IllegalArgumentException</a></dt>
<dd>
This error is caused by the Pages <tt>onIllegalArgumentClick()</tt> method throwing a 
<tt>IllegalArgumentException</tt>. Note how the error report shows you the exact line
where the error occurred. Click will do this if it can find the Java source code 
on the classpath or under the WEB-INF directory.
</dd>

<dt><a href="${missingMethodLink.href}">NoSuchMethodException</a></dt>
<dd>
This error is caused by a Control action listener being set to a method which 
doesn't exist. Typically a typo error when setting Control listeners. 
When the control attempts to call the listeners callback method it will throw a 
<tt>NoSuchMethodException</tt>. In this example the Java source code
is not available, so the error source is not highlighted.
</dd>

<dt><a href="${brokenBorderLink.href}">Broken Page Border Template</a></dt>
<dd>
This error is caused by an invalid Velocity expression in a page border template.
When Velocity tries to parse this expression it will throw a 
<tt>ParseErrorException</tt>. At this point no output will have been written to
the <tt>HttpServletResponse</tt> and the ErrorPage will render the error report
in the error.htm page template.
Note these types of exceptions are pretty rare. Most of the time Velocity will ignore 
template errors and simply render the invalid template code.
</dd>


<dt><a href="${brokenContentLink.href}">Broken Page Content Template</a></dt>
<dd>
This is another example of an invalid Velocity expression, but this time it is
contained in the page content template. When a exception occurs in a content template, 
Velocity will be performing a merge of the Page model and the border template, 
and including the content template. At this point Velocity will most probably have 
written border template output to the <tt>HttpServletResponse</tt> so the
<tt>ClickServlet</tt> appends the error report to the response output stream before 
it is closed.
</dd>


<dt><a href="${brokenRendererLink.href}">Broken Renderer</a></dt>
<dd>
This error is caused by a Page model object throwing a NPE when being rendered by 
Velocity. When Velocity tries to merge the page model with the template, it will
call the objects <tt>toString()</tt> method which throws a <tt>NullPointerException</tt>.
As this error usually occurs after some contents has been written to the 
<tt>HttpServletResponse</tt> Click will append the error report
to the end of the response.
<ul style="margin-top: 0.5em;">
   <li>Line 1</li>
   <li><a href="${brokenRendererLink.href}">$brokenRenderer</a> &nbsp; &lt;- clicking on link 
       will add <tt>BrokenRenderer</tt> to page model</li>
   <li>Line 3</li>
</ul>
</dd>


<dt><a href="missing.htm">Page Not Found</a></dt>
<dd>
When the ClickServlet cannot find a requested page it will render the 
<a href="click/not-found.htm">click/not-found.htm</a> page.<br/>
You can custome is this page templates to suite your own needs.
</dd>


</dl>