JSF composite:attribute with f:attribute conversio

问题:

I'm implementing a JSF component and need to conditionally add some attributes. This question is similar to a previous JSF: p:dataTable with f:attribute results in "argument type mismatch" error, but with a completely different error message, so I raised a new question.

<composite:interface>
    <composite:attribute name="filter" required="false" default="false"
                         type="java.lang.Boolean"/>
    <composite:attribute name="rows" required="false" default="15"
                         type="java.lang.Integer"/>
    ...
</composite:interface>

<composite:implementation>
  <p:dataTable ivar="p" value="#{cc.attrs.dm}">
    <c:if test="#{cc.attrs.filter}">
      <f:attribute name="paginator" value="#{true}"/>
      <f:attribute name="rows" value="#{cc.attrs.rows}"/>
    </c:if>
    ...
  <p:dataTable>
</composite:implementation>

This results in an error java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer. Even if I manually set this, I get errors:

<f:attribute name="rows" value="15"/>    ... argument type mismatch
<f:attribute name="rows" value="#{15}"/> ... java.lang.Long cannot be cast
                                             to java.lang.Integer

If I add the attribute directly, there is no exception and the correct number of rows is diplayed:

<p:dataTable var="p" value="#{cc.attrs.dm}" rows="#{cc.attrs.rows}">

回答1:

This is indeed an unfortunate corner case with numbers in EL and composite component attributes. There's no solution for this. The type information is not available in #{cc.attrs} when used in <f:attribute> and thus treated as String. The #{15} cannot be represented as an integer in EL either, all numbers are always implicitly treated as Long when the type information is absent. The ClassCastException can be prevented by using a tag file instead of a composite component.

Your best bet is doing the check in the actual rows attribute itself.

<p:dataTable ... rows="#{cc.attrs.filter ? cc.attrs.rows : null}">