多级缓存的实现---责任链模式
时间：2021-07-01 10:21:17
帮助过：6人阅读
多级缓存责任链模式。
* client提交给 hander，hander发现责任链上能处理该任务的函数，处理；可以归纳为：用一系列类(classes)试图处理一个请求request,这些类之间是一个松散的耦合, 唯一共同点是在他们之间传递request. 也就是说，来了一个请求，A类先处理，如果没有处理，就传递到B类处理，如果没有处理，就传递到C类处理，就这样象一个链条(chain)一样传递下去。
- /**
- * \责任链模式，其目的是组织一个对象链处理一个如方法调用的请求。
- *
- * 最著名的责任链示例：多级缓存。
- * client提交给 hander，hander发现责任链上能处理该任务的函数，处理；
- * 可以归纳为：用一系列类(classes)试图处理一个请求request,这些类之间是一个松散的耦合,
- * 唯一共同点是在他们之间传递request. 也就是说，来了一个请求，A类先处理，如果没有处理，
- * 就传递到B类处理，如果没有处理，就传递到C类处理，就这样象一个链条(chain)一样传递下去。
- */
-
-
- /**
- * The Handler abstraction. Objects that want to be a part of the
- * ChainOfResponsibility must implement this interface directly or via
- * inheritance from an AbstractHandler.
- * 处理抽象类，对象如果想成为责任链的一部分必须直接实现这个接口或
- * 继承一个抽象的处理类
- */
- interface KeyValueStore{
- /**
- * Obtain a 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.
- * 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。
- */
- 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.
- * 理想情况下，责任链上最后的具体处理类，加入链上，将是最后被调用的节点。
- */
- 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.
- * 在缓存没命中的情况下，转发到下一个处理对象
- */
- 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.
- * 不用关心调用的具体实现的外部具体具体处理程序；背后是责任链。
- */
- 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.enbttel'
- )
- );
- // in development, we skip cache and pass $store directly to FrontEnd
- $cache = new InMemoryKeyValueStore($store);
- $frontEnd = new FrontEnd($cache);
- echo $frontEnd->get('ia'). "\n";
- echo $frontEnd->getEscaped('hh'). "\n";
- /**
- * expect: ...
- * Isaac Asimov
- * Helmut Hei.enbttel
- *
- * 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。
- */
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