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

## Using a Custom Component

To use a custom component in a page, you add the custom tag associated with the component to the page.

As explained in Defining the Custom Component Tag in a Tag Library Descriptor, you must ensure that the TLD that defines any custom tags is packaged in the application if you intend to use the tags in your pages. TLD files are stored in the `WEB-INF/` directory or subdirectory of the WAR file or in the `META-INF/` directory or subdirectory of a tag library packaged in a JAR file.

You also need to include a namespace declaration in the page so that the page has access to the tags. The custom tags for the Duke’s Bookstore case study are defined in `bookstore.taglib.xml`. The `ui:composition` tag on the `index.xhtml` page declares the namespace defined in the tag library:

    <ui:composition xmlns="http://www.w3.org/1999/xhtml"
                    xmlns:ui="http://xmlns.jcp.org/jsf/facelets"
                    xmlns:h="http://xmlns.jcp.org/jsf/html"
                    xmlns:f="http://xmlns.jcp.org/jsf/core"
                    xmlns:bookstore="http://dukesbookstore"
                    template="./bookstoreTemplate.xhtml">

Finally, to use a custom component in a page, you add the component’s tag to the page.

The Duke’s Bookstore case study includes a custom image map component on the `index.xhtml` page. This component allows you to select a book by clicking on a region of the image map:

    ...
    <h:graphicImage id="mapImage"
                    name="book_all.jpg"
                    library="images
                    alt="#{bundle.chooseLocale}"
                    usemap="#bookMap" />
    <bookstore:map id="bookMap"
                   current="map1"
                   immediate="true"
                   action="bookstore">
        <f:actionListener
            type="javaeetutorial.dukesbookstore.listeners.MapBookChangeListener" />
        <bookstore:area id="map1" value="#{Book201}"
                        onmouseover="resources/images/book_201.jpg"
                        onmouseout="resources/images/book_all.jpg"
                        targetImage="mapImage" />
        ...
        <bookstore:area id="map6" value="#{Book207}"
                        onmouseover="resources/images/book_207.jpg"
                        onmouseout="resources/images//book_all.jpg"
                        targetImage="mapImage" />
    </bookstore:map>

The standard `h:graphicImage` tag associates an image (`book_all.jpg`) with an image map that is referenced in the `usemap` attribute value.

The custom `bookstore:map` tag that represents the custom component, `MapComponent`, specifies the image map and contains a set of `bookstore:area` tags. Each custom `bookstore:area` tag represents a custom `AreaComponent` and specifies a region of the image map.

On the page, the `onmouseover` and `onmouseout` attributes specify the image that is displayed when the user performs the actions described by the attributes. The custom renderer also renders an `onclick` attribute.

In the rendered HTML page, the `onmouseover`, `onmouseout`, and `onclick` attributes define which JavaScript code is executed when these events occur. When the user moves the mouse over a region, the `onmouseover` function associated with the region displays the map with that region highlighted. When the user moves the mouse out of a region, the `onmouseout` function redisplays the original image. When the user clicks a region, the `onclick` function sets the value of a hidden `input` tag to the ID of the selected area and submits the page.

When the custom renderer renders these attributes in HTML, it also renders the JavaScript code. The custom renderer also renders the entire `onclick` attribute rather than letting the page author set it.

The custom renderer that renders the HTML `map` tag also renders a hidden `input` component that holds the current area. The server-side objects retrieve the value of the hidden `input` field and set the locale in the `FacesContext` instance according to which region was selected.

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