代理模式（Proxy），它是对简单处理程序（或指针）的增强，用于引用一个对象：这个指针被代理（Proxy）对象取代，代理对象位于客户端（Client）和真实执行程序之间，指针有一个可被多个目标利用的钩子。
从技术上讲，这种模式在客户端和真实主体（RealSubject）之间插入一个代理对象，维护subject接口和用不同的方式委派它的方法。代理可以透明地做任何事情：懒散创建RealSubject或载入数据，与其它机器交换消息，写时复制策略等。这与HTTP代理有点类似，其客户端（如浏览器）和应用程序依赖于与HTTP服务器的联系，代理在管理连接时可以完成其它任务，如访问控制和缓存大型下载文件。
代理模式的对象图与装饰模式对象图在结构上类似，但表达的目的各有不同，装饰者给对象动态增加行为，而代理则控制来自客户端的访问。此外，代理只在需要时才创建RealSubject。
◆客户端（Client）：取决于主体（Subject）实现；◆主体（Subject）：RealSubject的抽象；
◆真实主体（RealSubject）：完成代价高昂的工作或包含大量的数据；
◆代理（Proxy）：为Client提供一个与Subject一致的引用，仅在需要时才创建RealSubject实例或与RealSubject实例通信。 1、对象-关系映射（Orms）在运行中创建代理作为实体类的子类，以实现懒散加载（虚拟代理），这个代理会覆盖所有实体方法，在前面追加一个载入程序，在方法被真正调用前不会包含任何数据，Orms代理支持对象间的双向关系，不用加载整个数据库，因为它们被置于当前加载对象图的边界。
2、Java RMI使用远程代理对象（远程代理），当它们的方法被调用时，代理序列化参数，执行网络上的请求，委托调用另一个节点上的真实对象，这种技术允许透明地调用远程对象，不用担心它们是否在同一台机器上，但这种透明度很容易会使执行速度变慢。
下面的代码示例实现了一个ImageProxy，推迟了图像数据的加载。
代码如下:
/**
* 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
* 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
以上代码实现了PHP的代理模式。简单来讲，代理模式就是为其他对象提供一个代理以控制对这个对象的访问。
