Conditionally render element's attribute in a composite component

问题

I have the following composite component:

<?xml version="1.0" encoding="UTF-8"?>
<ui:component xmlns="http://www.w3.org/1999/xhtml"
    xmlns:h="http://java.sun.com/jsf/html"
    xmlns:ui="http://java.sun.com/jsf/facelets"
    xmlns:c="http://java.sun.com/jsp/jstl/core"
    xmlns:f="http://java.sun.com/jsf/core"
    xmlns:p="http://primefaces.org/ui"
    xmlns:fn="http://java.sun.com/jsp/jstl/functions"
    xmlns:composite="http://java.sun.com/jsf/composite">

    <composite:interface>
        <composite:attribute required="true" name="field" />
        <composite:attribute required="true" name="value" />
        <composite:attribute required="false" name="size"/>
    </composite:interface>

    <composite:implementation>
    ...
            <div class="wrapper">
                <h:inputText value="#{cc.attrs.value}"
                    id="#{field.id}" 
                    rendered="#{field.rendered}" 
                    size="#{cc.attrs.size}">
                </h:inputText>
                <h:messages for="#{field.id}" styleClass="errorMessage"/>
            </div>
    ...
    </composite:implementation>
</ui:component>

The problem is that when I'm using this component without setting its size attribute, it still gets rendered as size=0 in the html input element.

What I want is to render the nested h:inputText's attribute only if it has a valid value (eg. not empty). Alternatively, I'd like to expose all attributes of the nested element if they are not overridden explicitly.

How would it be possible?

回答1:

You can use JSTL <c:if> to build the view conditionally and <f:attribute> to specify an attribute separately:

<h:inputText ...>
    <c:if test="#{not empty cc.attrs.size}">
        <f:attribute name="size" value="#{cc.attrs.size}" />
    </c:if>
</h:inputText>

An alternative is to specify a default for the composite component attribute:

<cc:attribute name="size" required="false" default="10" />

回答2:

Additional to BalusC's post:

You must use

type="int" in the cc:attribute-tag :

cc:attribute name="maxlength" type="int"

回答3:

I believe there is an alternate method for accessing attributes. I've used this with JSF 2 when accessing an attribute named with a java reserved keyword.

{cc.attrs['size']}

来源：https://stackoverflow.com/questions/12897202/conditionally-render-elements-attribute-in-a-composite-component