PHP设计模式之代理模式的深入解析

/** 
 * Subject interface. 
 * Client depends only on this abstraction. 
 */
interface Image 
{ 
    public function getWidth(); 

    public function getHeight(); 

    public function getPath(); 

    /** 
     * @return string   the image's byte stream 
     */
    public function dump(); 
} 

/** 
 * Abstract class to avoid repetition of boilerplate code in the Proxy 
 * and in the Subject. Only the methods which can be provided without 
 * instancing the RealSubject are present here. 
 */
abstract class AbstractImage implements Image 
{ 
    protected $_width; 
    protected $_height; 
    protected $_path; 
    protected $_data; 

    public function getWidth() 
    { 
 return $this->_width; 
    } 

    public function getHeight() 
    { 
 return $this->_height; 
    } 

    public function getPath() 
    { 
 return $this->_path; 
    } 
} 

/** 
 * The RealSubject. Always loads the image, even if no dump of the data 
 * is required. 
 */
class RawImage extends AbstractImage 
{ 
    public function __construct($path) 
    { 
 $this->_path = $path; 
 list ($this->_width, $this->_height) = getimagesize($path); 
 $this->_data = file_get_contents($path); 
    } 

    public function dump() 
    { 
 return $this->_data; 
    } 
} 

/** 
 * Proxy. Defers loading the image data until it becomes really mandatory. 
 * This class does its best to postpone the very expensive operations 
 * such as the actual loading of the BLOB. 
 */
class ImageProxy extends AbstractImage 
{ 
    public function __construct($path) 
    { 
 $this->_path = $path; 
 list ($this->_width, $this->_height) = getimagesize($path); 
    } 

    /** 
     * Creates a RawImage and exploits its functionalities. 
     */
    protected function _lazyLoad() 
    { 
 if ($this->_realImage === null) { 
     $this->_realImage = new RawImage($this->_path); 
 } 
    } 

    public function dump() 
    { 
 $this->_lazyLoad(); 
 return $this->_realImage->dump(); 
    } 
} 

/** 
 * Client class that does not use the data dump of the image. 
 * Passing blindly a Proxy to this class and to other Clients makes sense 
 * as the data would be loaded anyway when Image::dump() is called. 
 */
class Client 
{ 
    public function tag(Image $img) 
    { 
 return '; 
    } 
} 

$path = '/home/giorgio/shared/Immagini/kiki.png'; 
$client = new Client(); 

$image = new RawImage($path); // loading of the BLOB takes place 
echo $client->tag($image), "n"; 

$proxy = new ImageProxy($path); 
echo $client->tag($proxy), "n"; // loading does not take place even here