Abstract: High-level modules should not depend on low-level modules, both should rely on abstractions. Abstractions should not depend on details, details should depend on abstractions.
class A{ public function echo() { echo 'A'.PHP_EOL; } }class EchoT { protected $t; public function __construct() { $this->t = new A(); } public function echo(){ $this->t->echo(); } }
Initially, we all use the new method internally, and the EchoT class relies heavily on class A. Whenever class A changes, class EchoT must also change.
class EchoT { protected $t; public function __construct($t) //构造器注入由构造器注入到其中 { $this->t = $t; }
You can see that if you do this. On a large scale, we decouple the program. No matter how you change class A, class EchoT does not need to be changed. No longer dependent on A. But a new problem has come again. We only have A now. What if B or CDEFG comes?
interface T{ public function echo(); }class A{ public function echo() { echo 'A'.PHP_EOL; } }class B implements T{ public function echo() { echo 'B'.PHP_EOL; } }class EchoT { protected $t; public function __construct(T $t) //构造器注入由构造器注入到其中 { $this->t = $t; } public function echo(){ $this->t->echo(); } }
将T抽象出为接口,这样,EchoT类中的echo方法变成一个抽象的方法,不到运行那一刻,不知道他们的Method方式是怎么实现的。
function getT($str) { if(class_exists($str)){ return new $str(); } }
T要使用哪个是不明确的,因此,我们可以将其工厂化。【看上去很简单,在DI实际上有体现】
首先,我们看一下PHP的psr规范。
http://www.php-fig.org/psr/psr-11/
官方定义的接口
Psr\Container\ContainerInterface 包含两个方法function get($id);function has($id);
仔细看上面的工厂,是不是和get($id)很一致,PHP官方将其定义为容器(Container,我个人理解,就是一个复杂的工厂)
依赖注入容器
namespace Core;use Psr\Container\ContainerInterface;class Container implements ContainerInterface{ protected $instance = [];//对象存储的数组 public function __construct($path) { $this->_autoload($path); //首先我们要自动加载 psr-autoload } public function build($className) { if(is_string($className) and $this->has($className)) { return $this->get($className); } //反射 $reflector = new \ReflectionClass($className); if (!$reflector->isInstantiable()) { throw new \Exception("Can't instantiate ".$className); } // 检查类是否可实例化, 排除抽象类abstract和对象接口interface if (!$reflector->isInstantiable()) { throw new \Exception("Can't instantiate ".$className); } /** @var \ReflectionMethod $constructor 获取类的构造函数 */ $constructor = $reflector->getConstructor(); // 若无构造函数,直接实例化并返回 if (is_null($constructor)) { return new $className; } // 取构造函数参数,通过 ReflectionParameter 数组返回参数列表 $parameters = $constructor->getParameters(); // 递归解析构造函数的参数 $dependencies = $this->getDependencies($parameters); // 创建一个类的新实例,给出的参数将传递到类的构造函数。 $class = $reflector->newInstanceArgs($dependencies); $this->instance[$className] = $class; return $class; } /** * @param array $parameters * @return array */ public function getDependencies(array $parameters) { $dependencies = []; /** @var \ReflectionParameter $parameter */ foreach ($parameters as $parameter) { /** @var \ReflectionClass $dependency */ $dependency = $parameter->getClass(); if (is_null($dependency)) { // 是变量,有默认值则设置默认值 $dependencies[] = $this->resolveNonClass($parameter); } else { // 是一个类,递归解析 $dependencies[] = $this->build($dependency->name); } } return $dependencies; } /** * @param \ReflectionParameter $parameter * @return mixed * @throws \Exception */ public function resolveNonClass(\ReflectionParameter $parameter) { // 有默认值则返回默认值 if ($parameter->isDefaultValueAvailable()) { return $parameter->getDefaultValue(); } throw new \Exception($parameter->getName().' must be not null'); } /** * 参照psr-autoload规范 * @param $path */ public function _autoload($path) { spl_autoload_register(function(string $class) use ($path) { $file = DIRECTORY_SEPARATOR.str_replace('\\',DIRECTORY_SEPARATOR, $class).'.php'; if(is_file($path.$file)) { include($path.$file); return true; } return false; }); } public function get($id) { if($this->has($id)) { return $this->instance[$id]; } if(class_exists($id)){ return $this->build($id); } throw new ClassNotFoundException('class not found'); //实现的PSR规范的异常 } public function has($id) { return isset($this->instance[$id]) ? true : false; } }
$container = new Container('../');//假设这是路径$echoT = $container->get(\Test\EchoT::class); //假设echoT类的命名空间是\Test$echoT->echo();
这个时候,会出现一个问题:
// 检查类是否可实例化, 排除抽象类abstract和对象接口interface if (!$reflector->isInstantiable()) { throw new \Exception("Can't instantiate ".$className); } 因为接口T是无法实例化的,所以,一般在程序内,我们都加上别名(参照laravel框架) $container->alisa(\Test\T::class,\Test\T\A::class); //指定接口T使用类A(控制反转)
下面是alias方法
public function alias(string $key, $class, bool $singleton = true) { if($singleton) { $this->singleton[] = $class; } $this->aliases[$key] = $class; return $this; } //同时,我们需要在build的时候进行判断是否为别名 public function build($className) { if(is_string($className) and $this->has($className)) { return $this->get($className); } if(isset($this->aliases[$className])) { if(is_object($this->aliases[$className])) { return $this->aliases[$className]; } $className = $this->aliases[$className]; }
就此,一个简单的PHP容器就实现了。
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