php设计模式 Chain Of Responsibility (职责链模式)

<?php 
/** 
* 职责链模式 
* 
* 为解除请求的发送者和接收者之间的耦合,而使用多个对象都用机会处理这个请求,将这些对象连成一条链,并沿着这条链传递该请求,直到有一个对象处理它 
* 
*/ 
abstract class Handler 
{ 
protected $_handler = null; 
public function setSuccessor($handler) 
{ 
$this->_handler = $handler; 
} 
abstract function handleRequest($request); 
} 
class ConcreteHandlerZero extends Handler 
{ 
public function handleRequest($request) 
{ 
if($request == 0) 
{ 
echo "0<br/>"; 
} else { 
$this->_handler->handleRequest($request); 
} 
} 
} 
class ConcreteHandlerOdd extends Handler 
{ 
public function handleRequest($request) 
{ 
if($request % 2) 
{ 
echo $request." is odd<br/>"; 
} else { 
$this->_handler->handleRequest($request); 
} 
} 
} 
class ConcreteHandlerEven extends Handler 
{ 
public function handleRequest($request) 
{ 
if(!($request % 2)) 
{ 
echo $request." is even<br/>"; 
} else { 
$this->_handler->handleRequest($request); 
} 
} 
} 
// 实例一下 
$objZeroHander = new ConcreteHandlerZero(); 
$objEvenHander = new ConcreteHandlerEven(); 
$objOddHander = new ConcreteHandlerOdd(); 
$objZeroHander->setSuccessor($objEvenHander); 
$objEvenHander->setSuccessor($objOddHander); 
foreach(array(2,3,4,5,0) as $row) 
{ 
$objZeroHander->handleRequest($row); 
}