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多级缓存的实现---责任链模式

程序员文章站 2022-06-04 18:06:54
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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。
  1. /**
  2. * \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。
  3. *
  4. * 最著名的责任链示例:多级缓存。
  5. * client提交给 hander,hander发现责任链上能处理该任务的函数,处理;
  6. * 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,
  7. * 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,
  8. * 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。
  9. */
  10. /**
  11. * The Handler abstraction. Objects that want to be a part of the
  12. * ChainOfResponsibility must implement this interface directly or via
  13. * inheritance from an AbstractHandler.
  14. * 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
  15. * 继承一个抽象的处理类
  16. */
  17. interface KeyValueStore{
  18. /**
  19. * Obtain a value.
  20. * @param string $key
  21. * @return mixed
  22. */
  23. public function get($key);
  24. }
  25. /**
  26. * Basic no-op implementation which ConcreteHandlers not interested in
  27. * caching or in interfering with the retrieval inherit from.
  28. * 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。
  29. */
  30. abstract class AbstractKeyValueStore implements KeyValueStore{
  31. protected $_nextHandler;
  32. public function get($key){
  33. return $this->_nextHandler->get($key);
  34. }
  35. }
  36. /**
  37. * Ideally the last ConcreteHandler in the chain. At least, if inserted in
  38. * a Chain it will be the last node to be called.
  39. * 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。
  40. */
  41. class SlowStore implements KeyValueStore{
  42. /**
  43. * This could be a somewhat slow store: a database or a flat file.
  44. */
  45. protected $_values;
  46. public function __construct(array $values = array()){
  47. $this->_values = $values;
  48. }
  49. public function get($key){
  50. return $this->_values[$key];
  51. }
  52. }
  53. /**
  54. * A ConcreteHandler that handles the request for a key by looking for it in
  55. * its own cache. Forwards to the next handler in case of cache miss.
  56. * 在缓存没命中的情况下,转发到下一个处理对象
  57. */
  58. class InMemoryKeyValueStore implements KeyValueStore{
  59. protected $_nextHandler;
  60. protected $_cached = array();
  61. public function __construct(KeyValueStore $nextHandler){
  62. $this->_nextHandler = $nextHandler;
  63. }
  64. protected function _load($key){
  65. if (!isset($this->_cached[$key])) {
  66. $this->_cached[$key] = $this->_nextHandler->get($key);
  67. }
  68. }
  69. public function get($key){
  70. $this->_load($key);
  71. return $this->_cached[$key];
  72. }
  73. }
  74. /**
  75. * A ConcreteHandler that delegates the request without trying to
  76. * understand it at all. It may be easier to use in the user interface
  77. * because it can specialize itself by defining methods that generates
  78. * html, or by addressing similar user interface concerns.
  79. * Some Clients see this object only as an instance of KeyValueStore
  80. * and do not care how it satisfy their requests, while other ones
  81. * may use it in its entirety (similar to a class-based adapter).
  82. * No client knows that a chain of Handlers exists.
  83. * 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。
  84. */
  85. class FrontEnd extends AbstractKeyValueStore{
  86. public function __construct(KeyValueStore $nextHandler){
  87. $this->_nextHandler = $nextHandler;
  88. }
  89. public function getEscaped($key){
  90. return htmlentities($this->get($key), ENT_NOQUOTES, 'UTF-8');
  91. }
  92. }
  93. // Client code
  94. $store = new SlowStore(
  95. array(
  96. 'pd' => 'Philip K. Dick',
  97. 'ia' => 'Isaac Asimov',
  98. 'ac' => 'Arthur C. Clarke',
  99. 'hh' => 'Helmut Hei.enbttel'
  100. )
  101. );
  102. // in development, we skip cache and pass $store directly to FrontEnd
  103. $cache = new InMemoryKeyValueStore($store);
  104. $frontEnd = new FrontEnd($cache);
  105. echo $frontEnd->get('ia'). "\n";
  106. echo $frontEnd->getEscaped('hh'). "\n";
  107. /**
  108. * expect: ...
  109. * Isaac Asimov
  110. * Helmut Hei.enbttel
  111. *
  112. * 参与者:
  113. ◆Client(客户端):向Handler(处理程序)提交一个请求;
  114. ◆Handler(处理程序)抽象:接收一个请求,以某种方式满足它;
  115. ◆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。
  116. */
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