added Decorator pattern

Decorator/Decorator.php

@@ -0,0 +1,84 @@
+<?php
+
+namespace DesignPatterns;
+
+/**
+ * Decorator pattern
+ *
+ * Purpose:
+ * to dynamically add new functionality to class instances
+ *
+ * Examples:
+ * - Zend Framework: decorators for Zend_Form_Element instances
+ * - Web Service Layer: Decorators JSON and XML for a REST service (in this case, only one of these should be allowed of
+ *   course)
+ *
+ */
+class Webservice
+{
+    protected $_data;
+
+    /**
+     * an array to holds 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 $response;
+    }
+}
+
+interface WebserviceDecorator
+{
+    public function renderData($data);
+}
+
+class JsonDecorator implements WebserviceDecorator
+{
+    public function renderData($data)
+    {
+        return json_encode($data);
+    }
+}
+
+class XmlDecorator implements WebserviceDecorator
+{
+    public function renderData($data)
+    {
+        // do some fany conversion to xml from array ...
+        return simplexml_load_string($data);
+    }
+}
+
+$service = new Webservice(array('foo' => 'bar'));
+$service->addDecorator(new JsonDecorator());
+echo $service->renderData();