How to create a composite component for a datatable column?

The <my:mycolumn> element must be an instance of UIColumn as that's the only valid child of a UIData component during the render response phase. All other UIComponent types will be ignored, thus not rendered. A composite component is implicitly a UINamingContaner component, which isn't a UIColumn and therefore ignored.

A PrimeFaces <p:dataTable> with a backing component that extends UIColumn also won't work due to the wrong lifecycle of a composite component. The column has to be created during the view build time, while the composite component's body is created during view render time.

The solution is to create a tag file instead, which means an extra .taglib.xml file, yet it works flawlessly.

/WEB-INF/tags/column.xhtml:

<ui:composition
    xmlns="http://www.w3.org/1999/xhtml" 
    xmlns:f="http://java.sun.com/jsf/core"
    xmlns:h="http://java.sun.com/jsf/html"
    xmlns:ui="http://java.sun.com/jsf/facelets" 
    xmlns:rich="http://richfaces.org/rich">
    <rich:column>
        <f:facet name="header">HEADER</f:facet>
        <h:outputText value="#{val}" />
    </rich:column>
</ui:composition>

/WEB-INF/my.taglib.xml:

<?xml version="1.0" encoding="UTF-8"?>
<facelet-taglib 
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-facelettaglibrary_2_0.xsd"
    version="2.0">
    <namespace>http://example.com/my</namespace>
    <tag>
        <tag-name>column</tag-name>
        <source>tags/column.xhtml</source>
        <attribute>
            <description>Column value</description>
            <name>val</name>
        </attribute>
    </tag>
</facelet-taglib>

Note: The <attribute> entries are not mandatory, but are nice for documentation purposes, such as generated docs and IDE autocomplete.

/WEB-INF/web.xml:

<context-param>
    <param-name>javax.faces.FACELETS_LIBRARIES</param-name>
    <param-value>/WEB-INF/my.taglib.xml</param-value>
</context-param>

Usage:

<ui:composition
    xmlns="http://www.w3.org/1999/xhtml" 
    xmlns:f="http://java.sun.com/jsf/core"
    xmlns:h="http://java.sun.com/jsf/html"
    xmlns:ui="http://java.sun.com/jsf/facelets" 
    xmlns:rich="http://richfaces.org/rich"
    xmlns:my="http://example.com/my">
    <rich:dataTable value="#{values}" var="value">
        <my:column val="#{value}" />
    </rich:dataTable>
</ui:composition>