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

## Registering a Custom Renderer with a Render Kit

When the application developer creates a custom renderer, as described in Delegating Rendering to a Renderer, you must register it using the appropriate render kit. Because the image map application implements an HTML image map, the `AreaRenderer` and `MapRenderer` classes in the Duke’s Bookstore case study should be registered using the HTML render kit.

You register the renderer either by using the `@FacesRenderer` annotation, as described in Creating the Renderer Class, or by using the `render-kit` element of the application configuration resource file. Here is a hypothetical configuration of `AreaRenderer`:

    <render-kit>
        <renderer>
            <component-family>Area</component-family>
            <renderer-type>DemoArea</renderer-type>
            <renderer-class>
                dukesbookstore.renderers.AreaRenderer
            </renderer-class>
            <attribute>
                <attribute-name>onmouseout</attribute-name>
                <attribute-class>java.lang.String</attribute-class>
            </attribute>
            <attribute>
                <attribute-name>onmouseover</attribute-name>
                <attribute-class>java.lang.String</attribute-class>
            </attribute>
            <attribute>
                <attribute-name>styleClass</attribute-name>
                <attribute-class>java.lang.String</attribute-class>
            </attribute>
        </renderer>
        ...

Attributes specified in a `renderer` tag override any settings in the `@FacesRenderer` annotation.

The `render-kit` element represents a javax.faces.render.`RenderKit` implementation. If no `render-kit-id` is specified, the default HTML render kit is assumed. The `renderer` element represents a `javax.faces.render.Renderer` implementation. By nesting the `renderer` element inside the `render-kit` element, you are registering the renderer with the `RenderKit` implementation associated with the `render-kit` element.

The `renderer-class` is the fully qualified class name of the `Renderer`.

The `component-family` and `renderer-type` elements are used by a component to find renderers that can render it. The `component-family` identifier must match that returned by the component class’s `getFamily` method. The component family represents a component or set of components that a particular renderer can render. The `renderer-type` must match that returned by the `getRendererType` method of the tag handler class.

By using the component family and renderer type to look up renderers for components, the JavaServer Faces implementation allows a component to be rendered by multiple renderers and allows a renderer to render multiple components.

Each of the `attribute` tags specifies a render-dependent attribute and its type. The `attribute` element doesn’t affect the runtime execution of your application. Rather, it provides information to tools about the attributes the `Renderer` supports.

The object responsible for rendering a component (be it the component itself or a renderer to which the component delegates the rendering) can use facets to aid in the rendering process. These facets allow the custom component developer to control some aspects of rendering the component. Consider this custom component tag example:

    <d:dataScroller>
        <f:facet name="header">
            <h:panelGroup>
                <h:outputText value="Account Id"/>
                <h:outputText value="Customer Name"/>
                <h:outputText value="Total Sales"/>
            </h:panelGroup>
        </f:facet>
        <f:facet name="next">
            <h:panelGroup>
                <h:outputText value="Next"/>
                <h:graphicImage url="/images/arrow-right.gif" />
            </h:panelGroup>
        </f:facet>
        ...
    </d:dataScroller>

The `dataScroller` component tag includes a component that will render the header and a component that will render the Next button. If the renderer associated with this component renders the facets, you can include the following `facet` elements in the `renderer` element:

    <facet>
        <description>This facet renders as the header of the table. It should be
             a panelGroup with the same number of columns as the data.
        </description>
        <display-name>header</display-name>
        <facet-name>header</facet-name>
    </facet>
    <facet>
        <description>This facet renders as the content of the "next" button in
             the scroller. It should be a panelGroup that includes an outputText
             tag that has the text "Next" and a right arrow icon.
        </description>
        <display-name>Next</display-name>
        <facet-name>next</facet-name>
    </facet>

If a component that supports facets provides its own rendering and you want to include `facet` elements in the application configuration resource file, you need to put them in the component’s configuration rather than the renderer’s configuration.

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