结构型设计模式 - 享元 (缓存)Flyweight
作者：菜皮日记
- 2023-09-08 北京
本文字数：1981 字
阅读完需：约 6 分钟
简介
享元模式更常见的叫法是缓存或 cache，一个对象只创建一次，之后一直复用这一对象。
跟单例不同在于，单例是全局只有唯一一个对象，所有人一起用同一个对象，且该对象是提前预设好的，不能定制。
而享元则可以根据参数不同创建出不同的实例，不过实例一旦创建就只保留一份，之后再次创建相同参数的实例则返回该对象，供所有引用的地方使用，引用方之间共享同一份享元实例的数据。
过程有点像定制化的单例模式。
角色
Flyweight 享元类
定制化的业务实体，根据不同需要可能定制不同的享元类，但一旦创建出一个享元类，以后都复用这一个类
FlyweightFactory 享元工厂类
用来创建和缓存享元实体的地方
类图
类图
代码
class Flyweight{ private $sharedState;
public function __construct($sharedState) { $this->sharedState = $sharedState; }
public function operation($uniqueState): void { $s = json_encode($this->sharedState); $u = json_encode($uniqueState); echo "Flyweight: Displaying shared ($s) and unique ($u) state.\n"; }}
class FlyweightFactory{ private $flyweights = [];
public function __construct(array $initialFlyweights) { foreach ($initialFlyweights as $state) { $this->flyweights[$this->getKey($state)] = new Flyweight($state); } }
private function getKey(array $state): string { ksort($state);
return implode("_", $state); }
public function getFlyweight(array $sharedState): Flyweight { $key = $this->getKey($sharedState);
if (!isset($this->flyweights[$key])) { echo "FlyweightFactory: Can't find a flyweight, creating new one.\n"; $this->flyweights[$key] = new Flyweight($sharedState); } else { echo "FlyweightFactory: Reusing existing flyweight.\n"; }
return $this->flyweights[$key]; }
public function listFlyweights(): void { $count = count($this->flyweights); echo "\nFlyweightFactory: I have $count flyweights:\n"; foreach ($this->flyweights as $key => $flyweight) { echo $key . "\n"; } }}
$factory = new FlyweightFactory([ ["Chevrolet", "Camaro2018", "pink"], ["Mercedes Benz", "C300", "black"], ["Mercedes Benz", "C500", "red"], ["BMW", "M5", "red"], ["BMW", "X6", "white"],]);$factory->listFlyweights();
function addCarToPoliceDatabase( FlyweightFactory $ff, $plates, $owner, $brand, $model, $color) { echo "\nClient: Adding a car to database.\n"; $flyweight = $ff->getFlyweight([$brand, $model, $color]);
$flyweight->operation([$plates, $owner]);}
addCarToPoliceDatabase($factory, "CL234IR", "James Doe", "BMW", "M5", "red");
addCarToPoliceDatabase($factory, "CL234IR", "James Doe", "BMW", "X1", "red");
$factory->listFlyweights();
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output:
FlyweightFactory: I have 5 flyweights:Chevrolet_Camaro2018_pinkMercedes Benz_C300_blackMercedes Benz_C500_redBMW_M5_redBMW_X6_white
Client: Adding a car to database.FlyweightFactory: Reusing existing flyweight.Flyweight: Displaying shared (["BMW","M5","red"]) and unique (["CL234IR","James Doe"]) state.
Client: Adding a car to database.FlyweightFactory: Can't find a flyweight, creating new one.Flyweight: Displaying shared (["BMW","X1","red"]) and unique (["CL234IR","James Doe"]) state.
FlyweightFactory: I have 6 flyweights:Chevrolet_Camaro2018_pinkMercedes Benz_C300_blackMercedes Benz_C500_redBMW_M5_redBMW_X6_whiteBMW_X1_red
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