Using a Custom Component
Java Platform, Enterprise Edition (Java EE) 8
The Java EE Tutorial

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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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