[OmniFaces utilities] The
writeAttributes() method writes component attributes of the given property-HTML mapping of names, if it's not empty. Map key will be used as component property name and map value will be used as HTML attribute name.Method:
A
practical case of Renderers#writeAttributes() occurs
when we write a custom component that extends an existing component and inherits
its attributes. More precisely, we want to strictly refer to the mapping of
component property-HTML attribute names of the attributes to be written (e.g. property-HTML
mapping of names listed in HtmlGraphicImage, HtmlInputText, HtmlOutputText, etc). At
rendering phase of our custom component we have two alternatives:
·
nominate each HTML attribute name and invoke the UIComponent#getAttributes()#get(component_property_name)
·
collect the mapping of component property-HTML
attribute names of the attributes to be written in a Map and
invoke Renderers#writeAttributes()
The first
approach is a little bit clumsy. But, if we rely on the fact that JSF list the mapping
of component property-HTML attribute names of the attributes to be written in a
protected Java enum named, PropertyKeys, (see javax.faces.component.html classes) then
we can write a snippet of code capable to collect this mapping for any JSF
component, like this:
import
org.omnifaces.util.Renderers;
...
public class
MyComponent extends HtmlGraphicImage {
public class
MyComponent extends HtmlOutputText {
public class
MyComponent extends HtmlInputText {
...
public
static final Map<String, String> ATTRIBUTE_NAMES =
collectAttributeNames();
private
static Map<String, String> collectAttributeNames() {
Map<String, String> attributeNames = new
HashMap<>();
for (PropertyKeys propertyKey :
PropertyKeys.values()) {
String name = propertyKey.name();
// 'class' is the HTML equivalent of 'styleClass';
since 'class' is a reserved
// Java keyword it cannot appear in the
enum.
attributeNames.put(name,
"styleClass".equals(name) ?
"class"
: propertyKey.toString());
}
return Collections.unmodifiableMap(attributeNames);
}
Further,
in a method specific to rendering (e.g. encodeBegin()), we can
render the mapping, like below:
@Override
public void
encodeBegin(FacesContext context) throws IOException {
ResponseWriter writer =
context.getResponseWriter();
...
writeAttributes(writer, this, MyComponent.ATTRIBUTE_NAMES);
}
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