1.3. 工厂方法

1.3.1. 目的

The good point over the SimpleFactory is you can subclass it to implement different ways to create objects.

For simple cases, this abstract class could be just an interface.

这个模式是一个 “真正” 的设计模式，因为它遵循了依赖反转原则（Dependency Inversion Principle） 众所周知这个 “D” 代表了真正的面向对象程序设计。

它意味着工厂方法类依赖于类的抽象，而不是具体将被创建的类，这是工厂方法模式与简单工厂模式和静态工厂模式最重要的区别

1.3.2. UML 图

Alt FactoryMethod UML Diagram

1.3.3. 代码

你可以在 GitHub 上找到这些代码

Logger.php

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<?php declare(strict_types=1);

namespace DesignPatterns\Creational\FactoryMethod;

interface Logger
{
    public function log(string $message);
}

StdoutLogger.php

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<?php declare(strict_types=1);

namespace DesignPatterns\Creational\FactoryMethod;

class StdoutLogger implements Logger
{
    public function log(string $message)
    {
        echo $message;
    }
}

FileLogger.php

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<?php declare(strict_types=1);

namespace DesignPatterns\Creational\FactoryMethod;

class FileLogger implements Logger
{
    private string $filePath;

    public function __construct(string $filePath)
    {
        $this->filePath = $filePath;
    }

    public function log(string $message)
    {
        file_put_contents($this->filePath, $message . PHP_EOL, FILE_APPEND);
    }
}

LoggerFactory.php

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<?php declare(strict_types=1);

namespace DesignPatterns\Creational\FactoryMethod;

interface LoggerFactory
{
    public function createLogger(): Logger;
}

StdoutLoggerFactory.php

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<?php declare(strict_types=1);

namespace DesignPatterns\Creational\FactoryMethod;

class StdoutLoggerFactory implements LoggerFactory
{
    public function createLogger(): Logger
    {
        return new StdoutLogger();
    }
}

FileLoggerFactory.php

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<?php declare(strict_types=1);

namespace DesignPatterns\Creational\FactoryMethod;

class FileLoggerFactory implements LoggerFactory
{
    private string $filePath;

    public function __construct(string $filePath)
    {
        $this->filePath = $filePath;
    }

    public function createLogger(): Logger
    {
        return new FileLogger($this->filePath);
    }
}

1.3.4. 测试

Tests/FactoryMethodTest.php

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<?php declare(strict_types=1);

namespace DesignPatterns\Creational\FactoryMethod\Tests;

use DesignPatterns\Creational\FactoryMethod\FileLogger;
use DesignPatterns\Creational\FactoryMethod\FileLoggerFactory;
use DesignPatterns\Creational\FactoryMethod\StdoutLogger;
use DesignPatterns\Creational\FactoryMethod\StdoutLoggerFactory;
use PHPUnit\Framework\TestCase;

class FactoryMethodTest extends TestCase
{
    public function testCanCreateStdoutLogging()
    {
        $loggerFactory = new StdoutLoggerFactory();
        $logger = $loggerFactory->createLogger();

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

    public function testCanCreateFileLogging()
    {
        $loggerFactory = new FileLoggerFactory(sys_get_temp_dir());
        $logger = $loggerFactory->createLogger();

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