服务定位器用于管理一个系统中的所有服务。
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interface AbstractResourceDependent {}

class ResourceDependent implements AbstractResourceDependent {}

class ServiceLocator
{
    private static $cache = [];

    public static function getService(String $jndiName)
    {
    $service = self::$cache[$jndiName];

        if (null == $service) {

            if (AbstractResourceDependent::class == $jndiName) {
                $service = new ResourceDependent();
            }

            // 注册
            self::$cache[$jndiName] = $service;
        }

    return $service;
    }
}

class Resource
{
    private $abstractResourceDependent;

    public function __construct()
    {
        // 控制反转 - 控制权转移到服务定位器
        $this->abstractResourceDependent = ServiceLocator::getService(AbstractResourceDependent::class);
    }
}
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