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.


When you specify for example the standard <f:convertDateTime> by converterId="jakarta.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="jakarta.faces.DateTime" pattern="#{item.pattern}" locale="#{item.locale}" />

The converter ID of all standard Faces 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 the 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.


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

 <f:convertDateTime type="localDateTime" 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).

jakarta.faces.view.facelets.TagAttributeException: /showcase/taghandlers/converter.xhtml @53,101 locale="" Attribute did not evaluate to a String or Locale: null
    at com.sun.jsf-impl@4.0.0.SP01//com.sun.faces.facelets.tag.faces.ComponentSupport.getLocale(ComponentSupport.java:423)
    at com.sun.jsf-impl@4.0.0.SP01//com.sun.faces.facelets.tag.faces.core.ConvertDateTimeHandler.setAttributes(ConvertDateTimeHandler.java:89)
    at com.sun.jsf-impl@4.0.0.SP01//com.sun.faces.facelets.tag.faces.ConverterTagHandlerDelegateImpl.applyAttachedObject(ConverterTagHandlerDelegateImpl.java:117)

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.

Language Full date time pattern
English Saturday, February 24, 2024 at 12:56:57 AM Central European Standard Time
Spanish sábado, 24 de febrero de 2024, 0:56:57 (hora estándar de Europa central)
French samedi 24 février 2024 à 00:56:57 heure normale d’Europe centrale
German Samstag, 24. Februar 2024 um 00:56:57 Mitteleuropäische Normalzeit
Dutch zaterdag 24 februari 2024 om 00:56:57 Midden-Europese standaardtijd
Arabic السبت، 24 فبراير 2024 12:56:57 ص توقيت وسط أوروبا الرسمي
Hebrew יום שבת, 24 בפברואר 2024 בשעה 0:56:57 שעון מרכז אירופה (חורף)
Chinese 2024年2月24日星期六 中欧标准时间 上午12:56:57
Demo source code
<h:dataTable value="#{converterBean.locales}" var="locale">
        <f:facet name="header">Language</f:facet>
        <f:facet name="header">Full date time pattern</f:facet>
        <h:outputText value="#{now.zonedDateTime}">
            <o:converter converterId="jakarta.faces.DateTime" type="localDateTime" dateStyle="full" timeStyle="full" locale="#{locale}" />
Documentation & Sources