Proper example of Decorator pattern

Previous example was simply implementing a strategy pattern.

A key problem is that WebService made clear that it did no actual output of its own - it handed it off to 'decorators'.

A decorator should always wrap a class that already has its own complete, self-contained functionality.

In this way, they only enhance / modify it. An instance that is non-decorated should work fully by itself.

Note the distinguishing difference between this and sub-classing - here the enhancement is added dynamically, at runtime, and to one instance.

With sub-classing, the enhancement is added at compile / parse time, and is applied to all instances / uses of the subclass.
This commit is contained in:
Matt Iversen
2013-05-08 21:30:09 +10:00
committed by Dominik Liebler
parent 79c0808858
commit b8381e5a60

View File

@@ -14,71 +14,61 @@ namespace DesignPatterns;
* course)
*
*/
class Webservice
interface Renderer
{
public function renderData();
}
class Webservice implements Renderer
{
protected $_data;
/**
* an array to hold all added decorators, often there would be defaults set in this
* array, e.g. the service could be defaulted to use JSON and only for special APIs
* use XML
*
* @var array
*/
protected $_decorators = array();
public function __construct($data)
{
$this->_data = $data;
}
/**
*
*
* @param WebserviceDecorator $decorator
* @return void
*/
public function addDecorator(WebserviceDecorator $decorator)
{
$this->_decorators[] = $decorator;
}
/**
* @return string
*/
public function renderData()
{
$response = '';
foreach ($this->_decorators as $decorator) {
$response = $decorator->renderData($this->_data);
}
return $response;
return $this->_data;
}
}
interface WebserviceDecorator
abstract class Decorator
{
public function renderData($data);
}
class JsonDecorator implements WebserviceDecorator
{
public function renderData($data)
protected $_wrapped;
public function __construct($wrappable)
{
return json_encode($data);
$this->_wrapped = $wrappable;
}
}
class XmlDecorator implements WebserviceDecorator
class RenderInJson extends Decorator implements Renderer
{
public function renderData($data)
public function renderData()
{
// do some fancy conversion to xml from array ...
return simplexml_load_string($data);
$output = $this->_wrapped->renderData();
return json_encode($output);
}
}
class RenderInXml extends Decorator implements Renderer
{
public function renderData()
{
$output = $this->_wrapped->renderData();
// do some fany conversion to xml from array ...
return simplexml_load_string($output);
}
}
// Create a normal service
$service = new Webservice(array('foo' => 'bar'));
$service->addDecorator(new JsonDecorator());
// Wrap service with a JSON decorator for renderers
$service = new RenderInJson($service);
// Our Renderer will now output JSON instead of an array
echo $service->renderData();