The following topics and more will be covered in detail in my upcoming book with Neil Griffin, JavaServer Faces 2.0: The Complete Reference. Please enjoy this early access content!

One challenging aspect of designing JSF 2.0 was how to standardize Facelets. We wanted to standardize only the minimum amount that would still allow developers get the job done. Initially, we did not include binary custom tag handlers in the standard because most users of Facelets were simply using it to declare pages of existing UI components. Andy Schwartz and others advocated for the inclusion of a custom tag handler feature in the standard but I didn't want to just standardize what Jacob had initially done.

While Jacob's initial work for custom tag handlers was certainly effective, EG discussions with Ken Paulsen, creator of the JSFTemplating View Declaration Language led the EG to conclude that the standardization work for some of Facelets would best be left to JSF 2.1. In particular, Ken and EG member Imre Oßwald came up with something they called View Abstract Syntax Tree that would handle deeper aspects of Faces templating that they felt solved some of the flaws in the implementation of Facelets. Rather than overspecify, we came up with a simpler solution that still enables the most common usecases for custom tag handlers.

First, let's take a look at the custom.taglib.xml file. The manner and location for this file is exactly the same as before. In this example, (available in the Mojarra svn repo), the file lives at WEB-INF/classes/META-INF/custom.taglib.xml.

The java code for this class is shown next. At right, you see the stack trace for a breakpoint set on line 8.

The preceding code does nothing. But it's a start. Particurlarly useful is that ComponentConfig argument. This gives you access to a whole bunch of useful stuff. Note also that extends javax.faces.view.facelets.ComponentHandler. There are handlers for all the kinds of tags in JSF: converter, validator, component, and behavior.

In many cases, the only reason people were doing custom Facelet tags was so they could be notified when the component is built. To get this in JSF 2.0, just override the onComponentCreated() method, as shown in the next class.

The stack traces for onComponentCreated and onComponentPopulated are here and here, respectively.

If you really must have access to the apply method, and indeed override it, you can still do so. However, to preserve a clean separation between interface and implementation there is a little extra syntatic sugar you must endure. Sorry. Here's the code for a custom tag handler that overrides apply() and createMetaRuleset(). The stack trace for apply() is shown at left, while the one for createMetaRuleset() is available here.

As mentioned previously, there are handlers for all the different kinds of JSF artifacts that may appear in a Facelet page. The syntax in the .taglib.xml file is rather similar for all of them, but the one for the validator is shown next.

Finally, here's the code for this custom validator.

The callstacks for apply() and createMetaRuleset() are here and here

80% of the time, there is no need for any custom tag handlers. If you're doing your job right, the logic should be in the UIComponent, Validator, Converter, etc. However, for that extra 20% of the time, you can use the above practices to get the job done.

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