Java Platform, Enterprise Edition (Java EE) 8 The Java EE Tutorial

## Defining the Custom Component Tag in a Tag Library Descriptor

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>

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