PHP 服务定位器模式

这被认为是一种反模式！
对于某些人来说，服务定位器被认为是一种反模式。它违反了依赖倒置原则。服务定位器隐藏类的依赖关系，而不是像使用依赖注入那样暴露它们。如果这些依赖项发生变化，您可能会破坏使用它们的类的功能，从而使您的系统难以维护。

目的

实现松散耦合的架构以获得更好的可测试、可维护和可扩展的代码。DI 模式和服务定位器模式是逆控制模式的一种实现。

用法

使用ServiceLocator您可以为给定接口注册服务。通过使用该接口，您可以检索服务并在应用程序的类中使用它，而无需知道它的实现。您可以在引导程序上配置和注入服务定位器对象。

UML 图

代码

Service.php

<?php

namespace DesignPatterns\More\ServiceLocator;

interface Service
{

}

ServiceLocator.php

<?php

declare(strict_types=1);

namespace DesignPatterns\More\ServiceLocator;

use OutOfRangeException;
use InvalidArgumentException;

class ServiceLocator
{
    /**
     * @var string[][]
     */
    private array $services = [];

    /**
     * @var Service[]
     */
    private array $instantiated = [];

    public function addInstance(string $class, Service $service)
    {
        $this->instantiated[$class] = $service;
    }

    public function addClass(string $class, array $params)
    {
        $this->services[$class] = $params;
    }

    public function has(string $interface): bool
    {
        return isset($this->services[$interface]) || isset($this->instantiated[$interface]);
    }

    public function get(string $class): Service
    {
        if (isset($this->instantiated[$class])) {
            return $this->instantiated[$class];
        }

        $args = $this->services[$class];

        switch (count($args)) {
            case 0:
                $object = new $class();
                break;
            case 1:
                $object = new $class($args[0]);
                break;
            case 2:
                $object = new $class($args[0], $args[1]);
                break;
            case 3:
                $object = new $class($args[0], $args[1], $args[2]);
                break;
            default:
                throw new OutOfRangeException('Too many arguments given');
        }

        if (!$object instanceof Service) {
            throw new InvalidArgumentException('Could not register service: is no instance of Service');
        }

        $this->instantiated[$class] = $object;

        return $object;
    }
}

LogService.php

<?php

declare(strict_types=1);

namespace DesignPatterns\More\ServiceLocator;

class LogService implements Service
{

}

测试

Tests/ServiceLocatorTest.php

<?php

declare(strict_types=1);

namespace DesignPatterns\More\ServiceLocator\Tests;

use DesignPatterns\More\ServiceLocator\LogService;
use DesignPatterns\More\ServiceLocator\ServiceLocator;
use PHPUnit\Framework\TestCase;

class ServiceLocatorTest extends TestCase
{
    private ServiceLocator $serviceLocator;

    public function setUp(): void
    {
        $this->serviceLocator = new ServiceLocator();
    }

    public function testHasServices()
    {
        $this->serviceLocator->addInstance(LogService::class, new LogService());

        $this->assertTrue($this->serviceLocator->has(LogService::class));
        $this->assertFalse($this->serviceLocator->has(self::class));
    }

    public function testGetWillInstantiateLogServiceIfNoInstanceHasBeenCreatedYet()
    {
        $this->serviceLocator->addClass(LogService::class, []);
        $logger = $this->serviceLocator->get(LogService::class);

        $this->assertInstanceOf(LogService::class, $logger);
    }
}