Home > Backend Development > PHP Tutorial > How to parse PHP dependency injection

How to parse PHP dependency injection

巴扎黑
Release: 2023-03-15 09:26:02
Original
1408 people have browsed it


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.

First, let’s look at a piece of code:

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();
        }
}
Copy after login

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.

Let’s optimize the code

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;
        }
Copy after login

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?

面向接口

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();
        }
}
Copy after login

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。

工厂

function getT($str) {    if(class_exists($str)){        return new $str();
        }
}
Copy after login

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】

DI(重点来了)

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);
Copy after login

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)

dependency injection container

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;
        }
}
Copy after login

使用示例

$container = new Container('../');//假设这是路径$echoT = $container->get(\Test\EchoT::class);     //假设echoT类的命名空间是\Test$echoT->echo();
Copy after login

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)
Copy after login

针对接口

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];
                }
Copy after login

就此,一个简单的PHP容器就实现了。

The above is the detailed content of How to parse PHP dependency injection. For more information, please follow other related articles on the PHP Chinese website!

Related labels:
source:php.cn
Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
Popular Tutorials
More>
Latest Downloads
More>
Web Effects
Website Source Code
Website Materials
Front End Template