JSF 2 — Composite component with optional listener attribute on f:ajax

Question

I have a composite component that looks something like this:

Answer 1

You need to specify the method-signature attribute of the <cc:attribute> tag in order to treat the attribute value as a method expression. You can use the JSTL view build time tag <c:if> to conditionally add the <f:ajax> tag.

<cc:interface>
    <cc:attribute name="listener" method-signature="void listener()" />
</cc:interface>
<cc:implementation>
    <h:someComponent>
        <c:if test="#{cc.getValueExpression('listener') != null}">
            <f:ajax listener="#{cc.attrs.listener}" />
        </c:if>
    </h:someComponent>
</cc:implementation>

(the #{not empty cc.attrs.listener} won't work as EL would implicitly evaluate the attribute as a value expression)

Then you can use it as follows:

<my:someComposite listener="#{bean.listener}" />

---

Or when your environment doesn't support EL 2.2, then create a backing component:

@FacesComponent("someComponent")
public class SomeComponent extends UINamingContainer {

    public boolean isHasListener() {
        return getValueExpression("listener") != null;
    }

}

which is to be declared and used as

<cc:interface type="someComponent">
    <cc:attribute name="listener" method-signature="void listener()" />
</cc:interface>
<cc:implementation>
    <h:someComponent>
        <c:if test="#{cc.hasListener}">
            <f:ajax listener="#{cc.attrs.listener}" />
        </c:if>
    </h:someComponent>
</cc:implementation>

Answer 2

I've the same problems too, and my solution was create default value for the action method. I have only to create a class: MyComponent.java that contains all default methods signature.

<cc:interface>
    <cc:attribute name="listener" method-signature="void listener()"
                  default="#{myComponent.doNothing()}" />
</cc:interface>
<cc:implementation>
    <h:someComponent>
        <f:ajax listener="#{cc.attrs.listener}" />
    </h:someComponent>
</cc:implementation>

Answer 3

All of the above didn't work for me unfortunately, so I fiddled around and came up with the following solution.

<cc:interface type="someComponent">
    <cc:attribute name="listener" method-signature="void listener()" />
</cc:interface>
<cc:implementation>
    <h:someComponent>
        <p:ajax listener="#{cc.attrs.listener}" onstart="#{cc.attrs.containsKey('listener') ? '' : 'return false'}" />
    </h:someComponent>
</cc:implementation>

This will always bind the ajax behavior, but only execute it if there actually is a listener.