How to check presence of optional attribute inside a composite component

Question

I need to verify whether an optional attribute has been passed or not within my composite component. How can I achieve this?

<composite:interface>
    <composite:attribute name="attr1" />
    <composite:attribute name="attr2" required="false" /> <!-- means OPTIONAL -->
</composite:interface>
<composite:implementation>
    <!-- How I can verify here whether attr2 is present or not whenever this component is used? -->
</composite:implementation>

Setting the default attribute to xxx for <composite:attribute> is not what I'm looking for.

score 13 · Accepted Answer · answered Dec 04 '12 at 13:32

13

You could just check if #{not empty cc.attrs.attr2} evaluates to true.

E.g. inside the rendered attribute of an arbitrary component:

<composite:implementation>
    <h:panelGroup rendered="#{not empty cc.attrs.attr2}">
        Attribute attr2 is not empty!
    </h:panelGroup>
</composite:implementation>

answered Dec 04 '12 at 13:32

BalusC

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by the way it is checking the value of `attr2` is empty or not and rendering accordingly. – MyFist Dec 05 '12 at 06:46
It is not working as I expected. It is checking the VALUE of `attr2` is empty (null) or not and rendering accordingly. But I want to add a check (with in my CC implementation) if `attr2` itself is PRESENT or not. Say my check on `` should give me `true` as `attr2` itself is passed. AND `` should give me `false` as `attr2` itself is not passed. Please suggest. – MyFist Dec 05 '12 at 06:59
You could compare to `null`. `rendered="#{cc.attrs.attr2 != null}"`. – BalusC Dec 05 '12 at 10:45
What's the functional requirement for this strange approach? – BalusC Dec 05 '12 at 11:58
Sorry for late reply. There is no functional requirement but I want my CC component simple to look. – MyFist Dec 10 '12 at 17:54

score 4 · Answer 2 · answered Feb 15 '16 at 02:10

4

You can check to see if the expression exists using the method:

cc.getValueExpression('someAttribute')

<composite:implementation>
    <h:outputText rendered="#{cc.getValueExpression('attr2') ne null}">
        Attribute attr2 has been passed!
    </h:outputText>
</composite:implementation>

answered Feb 15 '16 at 02:10

twinj

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18
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If i were him, i would choose this one as accepted answer. – webyildirim Nov 07 '17 at 10:04
This is more helpful than the accepted answer, see also https://stackoverflow.com/a/11368475/7769052 – banan3'14 Dec 29 '22 at 10:07

score 1 · Answer 3 · answered Oct 06 '17 at 13:33

You can conditionally add attributes to component via:

<c:if><f:attribute>

Sample:

<composite:interface>
    <composite:attribute name="label" />
    <composite:attribute name="required" default="false" />
    <composite:attribute name="readonly" default="false" />
    <composite:attribute name="value" />
    <composite:attribute name="title" />
    <composite:attribute name="placeholder" />
    <composite:attribute name="maxlength" type="java.lang.Integer"/>
</composite:interface>
<composite:implementation>
    <p:inputText
      id="field"
      value="#{cc.attrs.value}">
        <c:if test="#{empty cc.attrs.maxLength}">
           <f:attribute name="maxlength" value="#{cc.attrs.maxlength}" />
        </c:if>
    </p:inputText>
</composite:implementation>

I Found the answer in:

How not to set an attribute of a component inside a composite component if it is empty?

This will result in a null pointer exception, you have to check for *not empty*: ` ` — Hannes Schneidermayer, Jun 19 '19 at 15:48

How to check presence of optional attribute inside a composite component

3 Answers3