@FacesRenderer(componentFamily = "Area", rendererType = "DemoArea")
public class AreaRenderer extends Renderer {
Java Platform, Enterprise Edition (Java EE) 8 The Java EE Tutorial |
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Both MapComponent
and AreaComponent
delegate all of their rendering
to a separate renderer. The section
Performing Encoding explains how
MapRenderer
performs the encoding for MapComponent
. This section
explains in detail the process of delegating rendering to a renderer
using AreaRenderer
, which performs the rendering for AreaComponent
.
To delegate rendering, you perform the tasks described in the following topics:
When delegating rendering to a renderer, you can delegate all encoding
and decoding to the renderer, or you can choose to do part of it in the
component class. The AreaComponent
class delegates encoding to the
AreaRenderer
class.
The renderer class begins with a @FacesRenderer
annotation:
@FacesRenderer(componentFamily = "Area", rendererType = "DemoArea")
public class AreaRenderer extends Renderer {
The @FacesRenderer
annotation registers the renderer class with the
JavaServer Faces implementation as a renderer class. The annotation
identifies the component family as well as the renderer type.
To perform the rendering for AreaComponent
, AreaRenderer
must
implement an encodeEnd
method. The encodeEnd
method of
AreaRenderer
retrieves the shape, coordinates, and alternative text
values stored in the ImageArea
bean that is bound to AreaComponent
.
Suppose that the area
tag currently being rendered has a value
attribute value of "book203"
. The following line from encodeEnd
gets
the value of the attribute "book203"
from the FacesContext
instance:
ImageArea ia = (ImageArea)area.getValue();
The attribute value is the ImageArea
bean instance, which contains the
shape
, coords
, and alt
values associated with the book203
AreaComponent
instance. Configuring Model
Data describes how the application stores these values.
After retrieving the ImageArea
object, the method renders the values
for shape
, coords
, and alt
by simply calling the associated
accessor methods and passing the returned values to the ResponseWriter
instance, as shown by these lines of code, which write out the 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");
The encodeEnd
method also renders the JavaScript for the onmouseout
,
onmouseover
, and onclick
attributes. The Facelets page needs to
provide only the path to the images that are to be loaded during an
onmouseover
or onmouseout
action:
<bookstore:area id="map3" value="#{Book203}"
onmouseover="resources/images/book_203.jpg"
onmouseout="resources/images/book_all.jpg"
targetImage="mapImage"/>
The AreaRenderer
class takes care of generating the JavaScript for
these actions, as shown in the following code from encodeEnd
. The
JavaScript that AreaRenderer
generates for the onclick
action sets
the value of the hidden field to the value of 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 lifecycle
to return back to the Restore View phase. This phase saves any state
information, including the value of the hidden field, so that a new
request component tree is constructed. This value is retrieved by the
decode
method of the MapComponent
class. This decode method is
called by the JavaServer Faces implementation during the Apply Request
Values phase, which follows the Restore View phase.
In addition to the encodeEnd
method, AreaRenderer
contains an empty
constructor. This is used to create an instance of AreaRenderer
so
that it can be added to the render kit.
The @FacesRenderer
annotation registers the renderer class with the
JavaServer Faces implementation as a renderer class. The annotation
identifies the component family as well as the renderer type.
Register the renderer with a render kit by using the @FacesRenderer
annotation (or by using the application configuration resource file, as
explained in Registering a Custom
Renderer with a Render Kit). During the Render Response phase, the
JavaServer Faces implementation calls the getRendererType
method of
the component’s tag handler to determine which renderer to invoke, if
there is one.
You identify the type associated with the renderer in the rendererType
element of the @FacesRenderer
annotation for AreaRenderer
as well as
in the renderer-type
element of the tag library descriptor.
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