Conditional rendering of f:param in JSF

Question

I'm using an <h:outputLink> as follows.

<c:set var="cid" value="1"/>
<c:set var="sid" value="2"/>

<h:outputLink value="Test.jsf">
    <h:outputText value="Link"/>

    <f:param name="cid" value="#{cid}"/>
    <f:param name="sid" value="#{sid}"/>
</h:outputLink>

_{This is just an example. Both of the query-string parameters are dynamic. So, <c:set> used here is just for the sake of demonstration.}

At any time, either one, both or none of the parameters may be present. In case, if only one or none of them is present then, parameter/s are unnecessarily appended to the URL which should not happen. Preventing unnecessary query-string parameters from being appended to the URL requires a conditional rendering of <f:param>.

JSTL <c:if> like the following

<c:if test="${not empty cid}">
    <f:param name="cid" value="#{cid}"/>
</c:if>

did not work.

How can it be made possible to conditionally render <f:param> inside <h:outputLink>?

Answer 1

The <f:param> has a disable (not disabled!) attribute for the purpose.

<f:param name="cid" value="#{cid}" disable="#{empty cid}" />
<f:param name="sid" value="#{sid}" disable="#{empty sid}" />

Note that this has a bug in Mojarra versions older than 2.1.15, because they typo'ed the actual UIParameter property to be disble instead of disable. See also issue 2312.

As to the <c:if> approach, that would only work if the #{cid} and #{sid} is available during view build time. In other words, it would fail if they are only available during view render time, e.g. when they depend on var of a repeater component. See also JSTL in JSF2 Facelets... makes sense?

See also:

• f:param tag attribute 'disable' is not work

Answer 2

Don't you like this kind of a solution?

<f:param name="#{cid == null ? '' : 'cid'}" value="#{cid}"/>
<f:param name="#{sid == null ? '' : 'sid'}" value="#{sid}"/>