Delegating Rendering to a Renderer

Creating the Renderer Class

Identifying the Renderer Type

Delegating Rendering to a Renderer

BothMapComponent andAreaComponent delegate all of their rendering to a separate renderer.The sectionPerforming Encoding explains howMapRenderer performs the encoding forMapComponent. This sectionexplains in detail the process of delegating rendering to a renderer usingAreaRenderer,which performs the rendering forAreaComponent.

To delegate rendering, you perform these tasks:

• Create theRenderer class.

• Register the renderer with a render kit (explained inRegistering a Custom Renderer with a Render Kit).

• Identify the renderer type in the component’s tag handler.

Creating the Renderer Class

When delegating rendering to a renderer, you can delegate all encoding and decodingto the renderer, or you can choose to do part of itin the component class. TheAreaComponent class delegates encoding to theAreaRenderer class.

To perform the rendering forAreaComponent,AreaRenderer must implement anencodeEnd method. TheencodeEndmethod ofAreaRenderer retrieves the shape, coordinates, and alternative text values stored in theImageArea bean that is bound toAreaComponent. Suppose that thearea tag currently beingrendered has avalue attribute value of"fraA". The following line fromencodeEnd gets the value of the attribute"fraA" from theFacesContext instance.

ImageArea ia = (ImageArea)area.getValue();

The attribute value is theImageArea bean instance, which contains theshape,coords,andalt values associated with thefraAAreaComponent instance.Configuring Model Data describes how theapplication stores these values.

After retrieving theImageArea object, it renders the values forshape,coords, andaltby simply calling the associated accessor methods and passing the returned values totheResponseWriter instance, as shown by these lines of code, which write outthe shape and coordinates:

writer.startElement("area", area);writer.writeAttribute("alt", iarea.getAlt(), "alt");writer.writeAttribute("coords", iarea.getCoords(), "coords");writer.writeAttribute("shape", iarea.getShape(), "shape");

TheencodeEnd method also renders the JavaScript for theonmouseout,onmouseover, andonclickattributes. The page author need only provide the path to the images thatare to be loaded during anonmouseover oronmouseout action:

<bookstore:area value="#{fraA}"     onmouseover="/template/world_france.jpg"     onmouseout="/template/world.jpg" targetImage="mapImage" />

TheAreaRenderer class takes care of generating the JavaScript for these actions, asshown in the following code fromencodeEnd. The JavaScript thatAreaRenderer generates fortheonclick action sets the value of the hidden field to the valueof the current area’s component ID and submits the page.

sb = new StringBuffer("document.forms[0][’").    append(targetImageId).append("’].src=’");sb.append(getURI(context,     (String) area.getAttributes().get("onmouseout")));sb.append("’");writer.writeAttribute("onmouseout", sb.toString(),     "onmouseout");sb = new StringBuffer("document.forms[0][’").    append(targetImageId).append("’].src=’");sb.append(getURI(context,     (String) area.getAttributes().get("onmouseover")));sb.append("’");writer.writeAttribute("onmouseover", sb.toString(),     "onmouseover");sb = new StringBuffer("document.forms[0][’");sb.append(getName(context, area));sb.append("’].value=’");sb.append(iarea.getAlt());sb.append("’; document.forms[0].submit()");writer.writeAttribute("onclick", sb.toString(), "value");writer.endElement("area");

By submitting the page, this code causes the JavaServer Faces life cycle toreturn back to the restore view phase. This phase saves any state information,including the value of the hidden field, so that a new request componenttree is constructed. This value is retrieved by thedecode method of theMapComponent class. Thisdecode method is called by the JavaServer Faces implementation duringthe apply request values phase, which follows the restore view phase.

In addition to theencodeEnd method,AreaRenderer contains an empty constructor. Thisis used to create an instance ofAreaRenderer so that it can beadded to the render kit.

Identifying the Renderer Type

During the render response phase, the JavaServer Faces implementation calls thegetRendererType methodof the component’s tag handler to determine which renderer to invoke, if thereis one.

ThegetRendererType method ofAreaTag must return the type associated withAreaRenderer. Youidentify this type when you registerAreaRenderer with the render kit, as described inRegistering a Custom Renderer with a Render Kit. Here is thegetRendererType method from theAreaTag class:

public String getRendererType() { return ("DemoArea");}

Creating the Component Tag Handler explains more about thegetRendererType method.

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