The same page on different devices, with different RenderKits in Java

Creator QR Code ISO/IEC18004 in Java The same page on different devices, with different RenderKits

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PhaseListeners are described in more detail in 9, but for now just know that a PhaseListener is an interface you implement when you want to have the system call back your application code as a request moves through the JSF lifecycle In this case, we want our PhaseListener to inspect the User-Agent header after the restore view phase and set the RenderKit appropriately, on a per-request basis, as shown here in this inner class:

public class RenderKitSelectorPhaseListener implements PhaseListener { public PhaseId getPhaseId() { return PhaseIdRESTORE_VIEW; }

private void setRenderKitFromUserAgent(FacesContext context, String userAgent) { // To implement this kind of feature in a robust way requires a lot // of research and will result in lots of heuristics This version // is very simple and just looks for the strings iPod or iPhone // to determine if the User-Agent is coming from an iPhone or iPod // touch if (userAgentcontains("iPod") || userAgentcontains("iPhone")) { contextgetViewRoot()setRenderKitId( AppleMobileRenderKitRENDER_KIT_ID); } } public void afterPhase(PhaseEvent event) { setRenderKitFromUserAgent(eventgetFacesContext(), eventgetFacesContext()getExternalContext() getRequestHeaderMap()get("User-Agent")); } public void beforePhase(PhaseEvent event) { } }

<lifecycle> <phase-listener>comjsfcomprefcomponentsrendererapplemobile RenderKitSelectorPhaseListener</phase-listener> </lifecycle>

This code exposes a very important subtlety with our choice of setting the RenderKit on a per-request basis We made this choice because we didn t want to push the awareness of which RenderKit to use into the session This is a trade-off between server memory and runtime speed performance In this case we chose to save server memory (and complexity) in favor of a sacrificing a little runtime speed The subtlety comes from how we must take action in the afterPhase( ) method of restore view because this is the earliest time in the lifecycle when contextgetViewRoot( ) returns non-null We need access to the UIViewRoot so that we can set its renderKitId property At this point, we have a working phase listener that sets the RenderKit to use on this run through the lifecycle

Part II:

Now we will show how to decorate the standard HTML_BASIC RenderKit, which all JSF implementations must provide This will give us the ability to provide a RenderKit that is exactly the same as the standard one, but only override specific Renderers to provide content for a specific client device type

package comjsfcomprefcomponentsrendererwrapper; import import import import import import import import javautilHashMap; javautilMap; javaxfacesFactoryFinder; javaxfacescontextFacesContext; javaxfacesrenderRenderKit; javaxfacesrenderRenderKitFactory; javaxfacesrenderRenderKitWrapper; javaxfacesrenderRenderer;

public abstract class BaseRenderKitWrapper extends RenderKitWrapper { private RenderKit basic; private Map<String, Map<String, Renderer>> myFamilies = new HashMap<String, Map<String, Renderer>>(); public BaseRenderKitWrapper() { RenderKitFactory factory = (RenderKitFactory) FactoryFindergetFactory(FactoryFinderRENDER_KIT_FACTORY); basic = factorygetRenderKit(FacesContextgetCurrentInstance(), "HTML_BASIC"); } @Override public RenderKit getWrapped() { return basic; } @Override public void addRenderer(String family, String rendererType, Renderer renderer) { Map<String, Renderer> renderersForFamily = myFamiliesget(family); if (null == renderersForFamily) { renderersForFamily = new HashMap<String, Renderer>(); myFamiliesput(family, renderersForFamily); } renderersForFamilyput(rendererType, renderer); } @Override public Renderer getRenderer(String family, String rendererType) { Renderer result = null; Map<String, Renderer> renderersForFamily = myFamiliesget(family); if (null != renderersForFamily) { result = renderersForFamilyget(rendererType);

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if (result instanceof BaseRendererWrapper) { ((BaseRendererWrapper)result)setBaseRenderKit(this); } } if (null == result) { result = basicgetRenderer(family, rendererType); } return result; } public Renderer getBaseRenderer(String family, String rendererType) { Renderer result = null; result = basicgetRenderer(family, rendererType); return result; } }

This class extends javaxfacesrenderRenderKitWrapper The wrapper concept is explained in 13 This concept boils down to extending a wrapper base class, overriding the abstract getWrapped( ) method, and then overriding only the minimum number of other methods as needed In the constructor, we obtain a reference to the threadsafe singleton HTML_BASIC RenderKit, which we also return from the getWrapped( ) method The other methods we override are getRenderer( ) and addRenderer( ) These two methods fulfill the basic contract of a RenderKit as a data structure that stores Renderer instances, as shown in the preceding HtmlHelloWorldRenderer example The data structure within a RenderKit implementation is commonly implemented as a two-level Map The keys in the outer map are component family identifiers Each key in the outer map is associated with an inner Map, in which the keys are renderer-type identifiers and the values are the actual Renderer instances In the preceding code, this data structure is the myFamilies instance variable In getRenderer( ) and addRenderer( ), we check myFamilies first when access to a Renderer is needed, and if no matching Renderer is found there, we call through to the RenderKit returned from getWrapped( ) In this way, we can override as many or as few of the Renderers from the standard HTML_BASIC RenderKit as needed Now that you understand how our RenderKit decoration works, it is time to show a concrete BaseRenderKitWrapper subclass, called AppleMobileRenderKit

package comjsfcomprefcomponentsrendererapplemobile; import comjsfcomprefcomponentsrendererwrapperBaseRenderKitWrapper; import javaxfacescontextFacesContext; public class AppleMobileRenderKit extends BaseRenderKitWrapper { public static final String RENDER_KIT_ID = "HTML_APPLEMOBILE"; public static final String RESOURCE_LIBRARY_NAME = "applemobile"; static String getRequestPathForResource(FacesContext context, String resourceName) { String result = null; String expressionString = "#{resource['" + RESOURCE_LIBRARY_NAME + ":" +

Part II: