Extending JavaServer Faces in Java

Encode QR Code ISO/IEC18004 in Java Extending JavaServer Faces

In all of these cases, the first argument to the StateHelper method is an enum There is no strict requirement for the first argument to be an enum, but it is very convenient and natural to use an enum for this purpose

Values are read from a StateHelper in two ways: Object eval(Serializable key) or Object eval(Serializable key, Object defaultValue) This is by far the most common approach, as was shown previously in the isValid( ) method It is used for values that were stored with a call to put(Serializable key, Object value) Object get(Serializable key) This method is used when the value was stored with a call to put(Serializable key, Object value) or void add(Serializable key, Object value)

Values are removed from a StateHelper in two ways: Object remove(Serializable key) This variant removes the underlying Map data structure that is written to when Object put(Serializable key, String mapKey, Object value) is called Object remove(Serializable key, Object valueOrKey) This variant is used when you want to remove an entry from an underlying List or Map data structure There is currently no need to remove simple values stored with a call to Object put(Serializable key, Object value), so no way to do so is provided You know how to use StateHelper to automatically managed any persistent state required in your custom UIComponent Let s continue the exploration of custom components by examining how to extract rendering code into a Renderer

One powerful feature that JSF has always had is the pluggable rendering concept The rationale for this feature is the fundamental principle that rendering logic should be separated from behavior The composite component feature exemplifies this principle more cleanly, but there is still value in learning to use the Renderer feature As stated in 7, a Renderer is a class that is responsible for taking a UIComponent instance and generating the output to show the component in a specific kind of client device, for example, a Web browser Let s do a trivial refactoring of the rendering code in HtmlHelloInput into the new HtmlHelloWorldRenderer

package comjsfcomprefcomponentsrenderer; import import import import import javaioIOException; javautilMap; javaxfacescomponentEditableValueHolder; javaxfacescomponentUIComponent; javaxfacescomponentUINamingContainer;

11:

javaxfacescontextFacesContext; javaxfacescontextResponseWriter; javaxfacesrenderFacesRenderer; javaxfacesrenderRenderer;

@FacesRenderer(componentFamily="javaxfacesInput", rendererType="HtmlHelloWorld") public class HtmlHelloWorldRenderer extends Renderer{ @Override public void decode(FacesContext context, UIComponent component) { // The only difference between this method and the variant in // HtmlHelloInput is the additional UIComponent argument } @Override public void encodeEnd(FacesContext context, UIComponent component) throws IOException { // The only difference between this method and the variant in // HtmlHelloInput is the additional UIComponent argument, // which is also passed through to the encodeInputField(), // encodeSubmitButton(), encodeOutputField() methods } }

A Renderer is responsible for encapsulating the client device dependent aspects of a UIComponent, all of which happen to be related to the component s appearance, hence the name renderer In a similar fashion to UIComponents, there is a runtime registry for Renderers, called a RenderKit The details behind RenderKits are discussed in detail in 13, but for now it is sufficient to know that a RenderKit is a data structure that contains Renderer instances and that this data structure is consulted by JSF when it comes time to send the HTML to the browser The @FacesRenderer annotation declares the HtmlHelloWorldRenderer, with a specific componentFamily, and rendererType The equivalent XML syntax for the faces-configxml file is shown here

<render-kit> <renderer> <component-family>javaxfacesInput</component-family> <renderer-type>HtmlHelloWorldRenderer</renderer-type> <renderer-class> comjsfcomprefcomponentsrendererHtmlHelloWorldRenderer </renderer-class> </renderer> </render-kit>

NOTE In the accompanying code sample, we didn t add either a <render-kit-id> or a <renderkit-class> as child elements of <render-kit> Omitting these simply means that the new renderer class will be added to the default render-kit at runtime More details on creating custom render-kits will be provided in 13 Similarly, with the @FacesRenderer annotation, the renderKit attribute is optional, and omitting it has the same result

Part II: