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Available since OmniFaces 1.4

The <o:param> is a component that extends the standard UIParameter to implement ValueHolder and thus support a Converter to convert the supplied value to string, if necessary.

You can use it the same way as <f:param>, you only need to change f: into o: to get the extra support for a Converter by usual means via the converter attribute of the tag, or the nested <f:converter> tag, or just automatically if a converter is already registered for the target class via @FacesConverter(forClass).

Also, if no value is specified, but children are present, then the encoded output of children will be returned as param value. This is useful when you want to supply JSF components or HTML as parameter of an unescaped <h:outputFormat>. For example,

<h:outputFormat value="#{bundle.paragraph}" escape="false">
    <o:param><h:link outcome="contact" value="#{bundle.contact}" /></o:param>
</h:outputFormat>

with this bundle

paragraph = Please {0} for more information.
contact = contact us

will result in the link being actually encoded as output format parameter value.

Demo

Using converter

We want to pass this example entity referenced by #{paramBean.exampleEntity} as request parameter: ExampleEntity[42, The meaning of life]

f:param, check the link URL, it's merely printing the example entity's toString()

o:param with converter, the param in the link URL represents the converted value

We could of course also have used #{paramBean.exampleEntity.id} as param value, but this is not DRY if you already have a converter for the entity and this is thus potentially maintenance-unfriendly.

Using JSF and HTML as param value

To learn about what's new in OmniFaces, check the What's new in OmniFaces 2.6.3 page.

Demo source code
<h3>Using converter</h3>
<p>
    We want to pass this example entity referenced by <code>\#{paramBean.exampleEntity}</code> as request parameter:
    <strong>#{paramBean.exampleEntity}</strong>
</p>
<p>
    <h:link value="f:param, check the link URL, it's merely printing the example entity's toString()">
        <f:param name="exampleEntity" value="#{paramBean.exampleEntity}" />
    </h:link>
</p>
<p>
    <h:link value="o:param with converter, the param in the link URL represents the converted value">
        <o:param name="exampleEntity" value="#{paramBean.exampleEntity}" converter="exampleEntityConverter" />
    </h:link>
</p>
<p>
    We could of course also have used <code>\#{paramBean.exampleEntity.id}</code> as param value, but this is not
    DRY if you already have a converter for the entity and this is thus potentially maintenance-unfriendly.
</p>

<h3>Using JSF and HTML as param value</h3>
<p>
    <f:loadBundle basename="org.omnifaces.showcase.i18n.text" var="text" />
    <o:outputFormat value="#{text['showcase.components.param.demo.whatsnew.link']}" var="_link">
        <f:param value="#{_omniFacesVersion}" />
    </o:outputFormat>
    <h:outputFormat value="#{text['showcase.components.param.demo.whatsnew']}" escape="false">
        <o:param><h:link outcome="#{text['showcase.whatsnew.outcome']}" value="#{_link}" /></o:param>
    </h:outputFormat>
</p>
Documentation & Sources