JSF same ID on rendered

Question

Let's say I am using rendered as basically a case statement. I have a label and message for an input field, but I want the field itself to change depending on the case. As such:

<p:inputText id="foo" value="#{myBean.params[paramKey]}" 
   rendered="#{paramIsInput}" />
<p:calendar  id="foo" value="#{myBean.params[paramKey]}" 
   rendered="#{paramIsCalendar}" />

If I do that then I get the following error: java.lang.IllegalStateException: Component ID j_idt64:foo has already been found in the view.

As a workaround I created lots of labels/messages for each param type and changed their ids. But this brings my question. If only one component with an id is actually rendered, why would it matter that I have multiple defined in my jsf file? Is there a way to keep them with all the same ID?

Answer 1

JSF component IDs are supposed to be unique during view build time already, not during view render time only. This way you effectively end up with two JSF components with the same ID which is indeed invalid. You'd like to effectively end up with one JSF component with the desired ID in the JSF component tree after view build time.

You can achieve this by populating the component during the view build time instead of generating its HTML output conditionally during the view render time. You can use the JSTL <c:if> tag for this.

<c:if test="#{paramIsInput}">
    <p:inputText id="foo" value="#{myBean.params[paramKey]}" />
</c:if>
<c:if test="#{paramIsCalendar}">
    <p:calendar id="foo" value="#{myBean.params[paramKey]}" />
</c:if>

This has however caveats: the <c:if test> condition can't depend on a variable which is only known during JSF render time. So it has not to depend on var of a JSF iterating component, or to be a property of a view scoped bean, etc.

See also:

• JSTL in JSF2 Facelets... makes sense?