omnifaces

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Available since OmniFaces 1.0

The <o:converter> is a taghandler that extends the standard <f:converter> tag family with support for deferred value expressions in all attributes. In other words, the converter attributes are not evaluated anymore on a per view build time basis, but just on every access like as with UI components and bean properties. This has among others the advantage that they can be evaluated on a per-iteration basis inside an iterating component, and that they can be set on a custom converter without needing to explicitly register it in a tagfile.

Usage

When you specify for example the standard <f:convertDateTime> by converterId="javax.faces.DateTime", then you'll be able to use all its attributes such as pattern and locale as per its documentation, but then with the possibility to supply deferred value expressions. 

<o:converter converterId="javax.faces.DateTime" pattern="#{item.pattern}" locale="#{item.locale}" />

The converter ID of all standard JSF converters can be found in their javadocs. First go to the javadoc of the class of interest, then go to CONVERTER_ID in its field summary and finally click the Constant Field Values link to see the value.

JSF 2.3 compatibility

The <o:converter> is currently not compatible with converters which are managed via JSF 2.3's new managed=true attribute set on the FacesConverter annotation, at least not when using Mojarra. Internally, the converters are wrapped in another instance which doesn't have the needed setter methods specified. In order to get them to work with <o:converter>, the managed=true attribute needs to be removed, so that OmniFaces ConverterManager will automatically manage them.

Demo

In the below demo, it was the intent to use <f:convertDateTime> as follows: 

 <f:convertDateTime type="both" dateStyle="full" timeStyle="full" locale="#{locale}" />

But this wouldn't even run, it will throw the following exception because the #{locale} isn't available during view build time (for a background explanation, check this Stack Overflow answer). 

 javax.faces.view.facelets.TagAttributeException: /taghandlers/converter @62,92 
 locale="" Attribute did not evaluate to a String or Locale: null
     at com.sun.faces.facelets.tag.jsf.ComponentSupport.getLocale(ComponentSupport.java:297)
     at com.sun.faces.facelets.tag.jsf.core.ConvertDateTimeHandler.setAttributes(ConvertDateTimeHandler.java:127)
     at com.sun.faces.facelets.tag.jsf.ConverterTagHandlerDelegateImpl.applyAttachedObject(ConverterTagHandlerDelegateImpl.java:130)

It works as intuitively expected with the <o:converter> as it allows a render time evaluation of attributes.

For another related use case, checkout the <o:validator> showcase page.

Demo
Language Full date time pattern
English Thursday, October 21, 2021 at 9:32:46 PM Greenwich Mean Time
Spanish jueves, 21 de octubre de 2021, 21:32:46 (hora del meridiano de Greenwich)
French jeudi 21 octobre 2021 à 21:32:46 heure moyenne de Greenwich
German Donnerstag, 21. Oktober 2021 um 21:32:46 Mittlere Greenwich-Zeit
Dutch donderdag 21 oktober 2021 om 21:32:46 Greenwich Mean Time
Arabic الخميس، ٢١ أكتوبر ٢٠٢١ ٩:٣٢:٤٦ م توقيت غرينتش
Hebrew יום חמישי, 21 באוקטובר 2021 בשעה 21:32:46 שעון גריניץ׳‏
Chinese 2021年10月21日星期四 格林尼治标准时间 下午9:32:46
Demo source code
<h:dataTable value="#{converterBean.locales}" var="locale">
    <h:column>
        <f:facet name="header">Language</f:facet>
        #{locale.displayLanguage}
    </h:column>
    <h:column>
        <f:facet name="header">Full date time pattern</f:facet>
        <h:outputText value="#{now}">
            <o:converter converterId="javax.faces.DateTime" type="both" dateStyle="full" timeStyle="full" locale="#{locale}" />
        </h:outputText>
    </h:column>
</h:dataTable>
Documentation & Sources

VDL documentation

API documentation

Java source code