1.3.1. 目的

对比简单工厂模式的优点是，您可以将其子类用不同的方法来创建一个对象。

举一个简单的例子，这个抽象类可能只是一个接口。

这种模式是「真正」的设计模式， 因为他实现了S.O.L.I.D原则中「D」的 「依赖倒置」。

这意味着工厂方法模式取决于抽象类，而不是具体的类。 这是与简单工厂模式和静态工厂模式相比的优势。

1.3.2. UML图

1.3.3. 代码

你可以在 GitHub 查看这段代码

Logger.php

<?php
namespace DesignPatterns\Creational\FactoryMethod;
interface Logger
{
    public function log(string $message);
}

StdoutLogger.php

<?php
namespace DesignPatterns\Creational\FactoryMethod;
class StdoutLogger implements Logger
{
    public function log(string $message)
    {
        echo $message;
    }
}

FileLogger.php

<?php
namespace DesignPatterns\Creational\FactoryMethod;
class FileLogger implements Logger
{
    /**
     * @var string
     */
    private $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

<?php
namespace DesignPatterns\Creational\FactoryMethod;
interface LoggerFactory
{
    public function createLogger(): Logger;
}

StdoutLoggerFactory.php

<?php
namespace DesignPatterns\Creational\FactoryMethod;
class StdoutLoggerFactory implements LoggerFactory
{
    public function createLogger(): Logger
    {
        return new StdoutLogger();
    }
}

FileLoggerFactory.php

<?php
namespace DesignPatterns\Creational\FactoryMethod;
class FileLoggerFactory implements LoggerFactory
{
    /**
     * @var string
     */
    private $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

<?php
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);
    }
}