职责链模式

/**
* chainOfResponsibility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);
}

参考文章 https://wenku.baidu.com/view/b4c78b4702768e9951e738fb.html