参与者： ◆Client（客户端）：向Handler（处理程序）提交一个请求； ◆Handler（处理程序）抽象：接收一个请求，以某种方式满足它； ◆ConcreteHandlers（具体的处理程序）：接收一个请求，设法满足它，如果不成功就委派给下一个处理程序。 下面的代码实现了一个最著名的责任链示例：多级缓存。 复制代码 代码如下: /** * The Handler abstraction. Objects that want to be a part of the * ChainOfResponsibility must implement this interface directly or via * inheritance from an AbstractHandler. */ interface KeyValueStore { /** * Obtain a html' target='_blank'>value. * @param string $key * @return mixed */ public function get($key); }
/** * Basic no-op implementation which ConcreteHandlers not interested in * caching or in interfering with the retrieval inherit from. */ abstract class AbstractKeyValueStore implements KeyValueStore { protected $_nextHandler;
public function get($key) { return $this- _nextHandler- get($key); } }
/** * Ideally the last ConcreteHandler in the chain. At least, if inserted in * a Chain it will be the last node to be called. */ class SlowStore implements KeyValueStore { /** * This could be a somewhat slow store: a database or a flat file. */ protected $_values;
public function __construct(array $values = array()) { $this- _values = $values; }
public function get($key) { return $this- _values[$key]; } }
/** * A ConcreteHandler that handles the request for a key by looking for it in * its own cache. Forwards to the next handler in case of cache miss. */ class InMemoryKeyValueStore implements KeyValueStore { protected $_nextHandler; protected $_cached = array();
public function __construct(KeyValueStore $nextHandler) { $this- _nextHandler = $nextHandler; }
protected function _load($key) { if (!isset($this- _cached[$key])) { $this- _cached[$key] = $this- _nextHandler- get($key); } }
public function get($key) { $this- _load($key); return $this- _cached[$key]; } }
/** * A ConcreteHandler that delegates the request without trying to * understand it at all. It may be easier to use in the user interface * because it can specialize itself by defining methods that generates * html, or by addressing similar user interface concerns. * Some Clients see this object only as an instance of KeyValueStore * and do not care how it satisfy their requests, while other ones * may use it in its entirety (similar to a class-based adapter). * No client knows that a chain of Handlers exists. */ class FrontEnd extends AbstractKeyValueStore { public function __construct(KeyValueStore $nextHandler) { $this- _nextHandler = $nextHandler; }
public function getEscaped($key) { return htmlentities($this- get($key), ENT_NOQUOTES, 'UTF-8'); } }
// Client code $store = new SlowStore(array('pd' = 'Philip K. Dick', 'ia' = 'Isaac Asimov', 'ac' = 'Arthur C. Clarke', 'hh' = 'Helmut Hei enbüttel')); // in development, we skip cache and pass $store directly to FrontEnd $cache = new InMemoryKeyValueStore($store); $frontEnd = new FrontEnd($cache);
