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Progressive Enhancement with JSF

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Progressive Enhancement is a philosophy of web design – start with simple pages, and build them up based on the capabilities of the browser viewing the page. It’s related to (and in some ways, the opposite of) the idea of Graceful Degradation, starting with a nice, fancy page, and dealing with any browser faults in an elegant manner.

Prehaps the simplest example to see this in action is the case of JavaScript being disabled in the browser – this is occasionally true for certain corporate clients concerned about security, and sometimes the case for very old browsers.

JSF handles this usecase pretty well – consider the following code:

   2 <f:ajax render="grace :text">
   3   <h:selectBooleanCheckbox value="#{grace.checked}"/>
   4 </f:ajax>

This creates a checkbox input with an onclick event handler registered. If there’s no JavaScript enabled, it will continue to function as thought the ajax tag wasn’t there at all. But the user will need to submit the form with a button press…

There is another way to handle this: we could instead create a link, which uses view parameters:


   1 <f:metadata>
   2     <f:viewParam name="checked" value="#{grace.checked}"/>
   3 </f:metadata>
   4 <h:link value="check me">
   5     <f:param name="checked" value="#{!grace.checked}"/>
   6 </h:link>

That works, but isn’t as clean looking as the first, ajax method. Combining these approachs should provide a better user experience – and doing so isn’t especially difficult:

   1 <f:metadata>
   2     <f:viewParam name="checked" value="#{grace.checked}"/>
   3 </f:metadata>
   4 <h:outputText id="text" value="Checked: #{grace.checked}"/>
   5 <h:form id="form">
   6     <h:panelGroup id="grace" layout="block">
   7         <h:panelGroup id="default">
   8             <h:link value="check me">
   9                 <f:param name="checked" value="#{!grace.checked}"/>
  10             </h:link>
  11         </h:panelGroup>
  12         <h:panelGroup id="enhanced" style="display: none">
  13             <f:ajax render="grace :text">
  14                 <h:selectBooleanCheckbox value="#{grace.checked}"/>
  15             </f:ajax>
  16         </h:panelGroup>
  17         <script type="text/javascript">
  18             var def = document.getElementById("form:default");
  19             var enh = document.getElementById("form:enhanced"); 
  20             def.style.display = "none";
  21             enh.style.display = "block";
  22         </script>
  23     </h:panelGroup>
  24 </h:form>

First, create two divs, one with the link and the other with the checkbox, which is hidden by default. If JavaScript is enabled, then hide the link and show the checkbox. This is the basic idea behind Progressive Enhancement – first, create something that you’ll be happy with in any browser, then add features (in this case, an Ajaxified checkbox) as needed.

That’s all for today. One personal note: Today is my last day officially employed by Sun Microsystems – I wasn’t offered a position at Oracle, and I’m currently actively looking for something. Please feel free to checkout my resume, and let me know if you know of any openings that you think might be a fit for me.

(This article originally published on my java.net blog on February 7, 2010.)


Written by jamesgdriscoll

February 9, 2010 at 11:21 PM

Posted in ajax, JSF

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