Configure input validation of components by the caller

JSF offers the possibility to use so called value holders in the interface of a composite. You can then configure the validation in the usage of the component.

More precisely, you can use cc:valueHolder in a cc:interface of a composite component. Define the name attribute which will be used to reference the value holder later. With the targets attribute you define which of the input fields should use the validation.

<cc:interface componentType="IvyComponent">
    <cc:valueHolder name="fullname" targets="form:firstname form:lastname"></cc:valueHolder>  
    <cc:valueHolder name="comment" targets="form:comment"></cc:valueHolder>
</cc:interface>

<cc:implementation>
    <h:form id="form">
        <p:messages></p:messages>
        <p:panelGrid columns="2">
            <p:outputLabel for="firstname" value="Firstname"></p:outputLabel>
            <p:inputText id="firstname" value="#{data.firstname}"></p:inputText>
            <p:outputLabel for="lastname" value="Lastname"></p:outputLabel>
            <p:inputText id="lastname" value="#{data.lastname}"></p:inputText>
            <p:outputLabel for="comment" value="Comment"></p:outputLabel>
            <p:inputText id="comment" value="#{data.comment}"></p:inputText>
            ...
        </p:panelGrid>
    </h:form>
</cc:implementation>

In the Html User Dialog that embeds the component you can now use f:validateRequired and its for attribute to reference to the value holder in the interface.

<ic:forms.ConfigureValidationComponent>
        <f:validateRequired for="fullname"></f:validateRequired>
        <f:validateLength for="comment" minimum="0" maximum="10"></f:validateLength>
</ic:forms.ConfigureValidationComponent>

Note: This question and answer was originally posted by Heinrich Spreiter on his Xpert.ivy Hacker blog. Henry, many thanks to you for your enthusiastic work.