PHP行为型模式之责任链模式

<?php
// 抽象处理器类
abstract class Handler
{
    protected $successor;
    public function setSuccessor(Handler $successor)
    {
        $this->successor = $successor;
    }
    abstract public function handleRequest($request);
}
// 具体处理器类A
class ConcreteHandlerA extends Handler
{
    public function handleRequest($request)
    {
        if ($request == "A") {
            echo "ConcreteHandlerA handles the request.\n";
        } else if ($this->successor != null) {
            $this->successor->handleRequest($request);
        }
    }
}
// 具体处理器类B
class ConcreteHandlerB extends Handler
{
    public function handleRequest($request)
    {
        if ($request == "B") {
            echo "ConcreteHandlerB handles the request.\n";
        } else if ($this->successor != null) {
            $this->successor->handleRequest($request);
        }
    }
}
// 客户端代码
$handlerA = new ConcreteHandlerA();
$handlerB = new ConcreteHandlerB();
$handlerA->setSuccessor($handlerB);
$handlerA->handleRequest("A");
$handlerA->handleRequest("B");

<?php
$handlerA = new ConcreteHandlerA();
$handlerB = new ConcreteHandlerB();
$handlerA->setSuccessor($handlerB);
$handlerA->handleRequest("A");
$handlerA->handleRequest("B");