Here is the xhtml of template:

<div xmlns:f="http://java.sun.com/jsf/core"
xmlns:h="http://java.sun.com/jsf/html"
xmlns:c="http://java.sun.com/jstl/core">
<c:if test="#{widget.mode == 'edit'}">
<h:inputHidden value="needed" validator="#{nomenclature_liste_nomenclature.validaterListeEtNomenclatureLiee}"
id="#{widget.id}">
<f:attribute name="firstElt"
value="#{layout.widgetMap['nomenclature_liee'].id}" />
<f:attribute name="secondElt"
value="#{layout.widgetMap['type_de_metadonnees'].id}" />
</h:inputHidden>
<h:message for="#{widget.id}" styleClass="errorMessage" />
</c:if>
</div>

Java code:

    public static Object retrieveInputComponentValue(UIComponent anchor, String componentId) {
        Map<String,Object> attributes = anchor.getAttributes();

        if(attributes != null)
        {
            String inputId = (String) attributes.get(componentId);

            UIInput component = (UIInput) anchor.findComponent(inputId);
            if(component != null)
            {
                return component.getLocalValue();
            }
        }
        return null;
    }