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> ## Creating Custom UI Components

> JavaServer Faces technology offers a basic set of standard, reusable UI components that enable page authors and application developers to quickly and easily construct UIs for web applications. But often an application requires a component that has additional functionality or requires a completely new component. JavaServer Faces technology allows a component writer to extend the standard components to enhance their functionality or create custom components.

> In addition to extending the functionality of standard components, a component writer might want to give a page author the ability to change the appearance of the component on the page. Or the component writer might want to render a component to a different client. Enabled by the flexible JavaServer Faces architecture, a component writer can separate the definition of the component behavior from its appearance by delegating the rendering of the component to a separate renderer. In this way, a component writer can define the behavior of a custom component once but create multiple renderers, each of which defines a different way to render the component to a particular kind of client device.

> As well as providing a means to easily create custom components and renderers, the JavaServer Faces design also makes it easy to reference them from the page through JSP custom tag library technology.

> This chapter uses the image map custom component from the Duke's Bookstore application (see The Example JavaServer Faces Application, page 308) to explain how a component writer can create simple custom components, custom renderers, and associated custom tags, and take care of all the other details associated with using the components and renderers in an application.