责任链模式

<?php
 
// 定义一个抽象处理者类
abstract class Handler
{
    private $nextHandler;
 
    public function setNext(Handler $handler): Handler
    {
        $this->nextHandler = $handler;
        return $handler;
    }
 
    public function handle(Request $request): void
    {
        if ($this->nextHandler) {
            $this->nextHandler->handle($request);
        }
    }
}
 
// 定义一个具体处理者类 A
class ConcreteHandlerA extends Handler
{
    public function handle(Request $request): void
    {
        if ($request->getRequestType() === 'TypeA') {
            echo "ConcreteHandlerA 处理请求\n";
        } else {
            parent::handle($request);
        }
    }
}
 
// 定义一个具体处理者类 B
class ConcreteHandlerB extends Handler
{
    public function handle(Request $request): void
    {
        if ($request->getRequestType() === 'TypeB') {
            echo "ConcreteHandlerB 处理请求\n";
        } else {
            parent::handle($request);
        }
    }
}
 
// 定义请求类
class Request
{
    private $requestType;
 
    public function __construct(string $type)
    {
        $this->requestType = $type;
    }
 
    public function getRequestType(): string
    {
        return $this->requestType;
    }
}
 
// 客户端代码
$requestA = new Request('TypeA');
$requestB = new Request('TypeB');
$requestC = new Request('TypeC');
 
$handlerA = new ConcreteHandlerA();
$handlerB = new ConcreteHandlerB();
 
$handlerA->setNext($handlerB);
 
echo "处理 RequestA:\n";
$handlerA->handle($requestA);
 
echo "\n处理 RequestB:\n";
$handlerA->handle($requestB);
 
echo "\n处理 RequestC:\n";
$handlerA->handle($requestC);