To use a custom tag, you declare it in a Tag Library Descriptor (TLD). The TLD file defines how the custom tag is used in a JavaServer Faces page. The web container uses the TLD to validate the tag. The set of tags that are part of the HTML render kit are defined in the HTML_BASIC TLD, available in the oJavaServer Faces standard HTML tag library.

The TLD file name must end with taglib.xml. In the Duke’s Bookstore case study, the custom tags area and map are defined in the file web/WEB-INF/bookstore.taglib.xml.

All tag definitions must be nested inside the facelet-taglib element in the TLD. Each tag is defined by a tag element. Here are the tag definitions for the area and map components:

<facelet-taglib xmlns="http://xmlns.jcp.org/xml/ns/javaee"
...>
    <namespace>http://dukesbookstore</namespace>
    <tag>
        <tag-name>area</tag-name>
        <component>
            <component-type>DemoArea</component-type>
            <renderer-type>DemoArea</renderer-type>
        </component>
    </tag>
    <tag>
        <tag-name>map</tag-name>
        <component>
            <component-type>DemoMap</component-type>
            <renderer-type>DemoMap</renderer-type>
        </component>
    </tag>
</facelet-taglib>

The component-type element specifies the name defined in the @FacesComponent annotation, and the renderer-type element specifies the rendererType defined in the @FacesRenderer annotation.

The facelet-taglib element must also include a namespace element, which defines the namespace to be specified in pages that use the custom component. See Using a Custom Component for information on specifying the namespace in pages.

The TLD file is located in the WEB-INF directory. In addition, an entry is included in the web deployment descriptor (web.xml) to identify the custom tag library descriptor file, as follows:

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