PHP设计模式 PHP 单例模式
注：单例模式可能被认为是一种“反模式”。为了获得更好的可测试性和可维护性，建议使用依赖注入。
目标
让应用只存在一个对象的实例，处理所有的调用。
例子
- 数据库连接器
- 日志记录器
- 应用程序的锁定文件（Lock file，理论上整个应用应该只有一个锁文件）
UML 图
代码
Singleton.php
<?php
declare(strict_types=1);
namespace DesignPatterns\Creational\Singleton;
use Exception;
final class Singleton
{
private static ?Singleton $instance = null;
/**
* gets the instance via lazy initialization (created on first usage)
*/
public static function getInstance(): Singleton
{
if (static::$instance === null) {
static::$instance = new static();
}
return static::$instance;
}
/**
* is not allowed to call from outside to prevent from creating multiple instances,
* to use the singleton, you have to obtain the instance from Singleton::getInstance() instead
*/
private function __construct()
{
}
/**
* prevent the instance from being cloned (which would create a second instance of it)
*/
private function __clone()
{
}
/**
* prevent from being unserialized (which would create a second instance of it)
*/
public function __wakeup()
{
throw new Exception("Cannot unserialize singleton");
}
}
测试
Tests/SingletonTest.php
<?php
declare(strict_types=1);
namespace DesignPatterns\Creational\Singleton\Tests;
use DesignPatterns\Creational\Singleton\Singleton;
use PHPUnit\Framework\TestCase;
class SingletonTest extends TestCase
{
public function testUniqueness()
{
$firstCall = Singleton::getInstance();
$secondCall = Singleton::getInstance();
$this->assertInstanceOf(Singleton::class, $firstCall);
$this->assertSame($firstCall, $secondCall);
}
}