什么是容器

在开发过程中，经常会用到的一个概念就是依赖注入。我们借助依懒注入来解耦代码，选择性的按需加载服务，而这些通常都是借助容器来实现。

容器实现对对象的统一管理，并且确保对象实例的唯一性

容器可以很轻易的找到有很多实现示例，如 PHP-DI 、 YII-DI 等各种实现，通常他们要么大而全，要么高度适配特定业务，与实际需要存在冲突。

出于需要，我们自己造一个轻量级的轮子，为了保持规范，我们基于 PSR-11 来实现。

PSR-11

PSR 是 php-fig 提供的标准化建议，虽然不是官方组织，但是得到广泛认可。PSR-11 提供了容器接口。它包含 ContainerInterface 和 两个异常接口，并提供使用建议。

/*** Describes the interface of a container that exposes methods to read its entries.*/
interface ContainerInterface
{/*** Finds an entry of the container by its identifier and returns it.** @param string $id Identifier of the entry to look for.** @throws NotFoundExceptionInterface  No entry was found for **this** identifier.* @throws ContainerExceptionInterface Error while retrieving the entry.** @return mixed Entry.*/public function get($id);/*** Returns true if the container can return an entry for the given identifier.* Returns false otherwise.** `has($id)` returning true does not mean that `get($id)` will not throw an exception.* It does however mean that `get($id)` will not throw a `NotFoundExceptionInterface`.** @param string $id Identifier of the entry to look for.** @return bool*/public function has($id);
}

实现示例

我们先来实现接口中要求的两个方法

abstract class AbstractContainer implements ContainerInterface
{protected $resolvedEntries = [];/*** @var array*/protected $definitions = [];public function __construct($definitions = []){foreach ($definitions as $id => $definition) {$this->injection($id, $definition);}}public function get($id){if (!$this->has($id)) {throw new NotFoundException("No entry or class found for {$id}");}$instance = $this->make($id);return $instance;}public function has($id){return isset($this->definitions[$id]);}

实际我们容器中注入的对象是多种多样的，所以我们单独抽出实例化方法。

    protected function make($name){if (isset($this->resolvedEntries[$name])) {return $this->resolvedEntries[$name];}$definition = $this->definitions[$name];$params = [];if (is_array($definition) && isset($definition['class'])) {$params = $definition;$definition = $definition['class'];unset($params['class']);}$object = $this->reflector($definition, $params);return $this->resolvedEntries[$name] = $object;}public function reflector($concrete, array $params = []){if ($concrete instanceof \Closure) {return $concrete($params);} elseif (is_string($concrete)) {$reflection = new \ReflectionClass($concrete);$dependencies = $this->getDependencies($reflection);foreach ($params as $index => $value) {$dependencies[$index] = $value;}return $reflection->newInstanceArgs($dependencies);} elseif (is_object($concrete)) {return $concrete;}}/*** @param \ReflectionClass $reflection* @return array*/private function getDependencies($reflection){$dependencies = [];$constructor = $reflection->getConstructor();if ($constructor !== null) {$parameters = $constructor->getParameters();$dependencies = $this->getParametersByDependencies($parameters);}return $dependencies;}/**** 获取构造类相关参数的依赖* @param array $dependencies* @return array $parameters* */private function getParametersByDependencies(array $dependencies){$parameters = [];foreach ($dependencies as $param) {if ($param->getClass()) {$paramName = $param->getClass()->name;$paramObject = $this->reflector($paramName);$parameters[] = $paramObject;} elseif ($param->isArray()) {if ($param->isDefaultValueAvailable()) {$parameters[] = $param->getDefaultValue();} else {$parameters[] = [];}} elseif ($param->isCallable()) {if ($param->isDefaultValueAvailable()) {$parameters[] = $param->getDefaultValue();} else {$parameters[] = function ($arg) {};}} else {if ($param->isDefaultValueAvailable()) {$parameters[] = $param->getDefaultValue();} else {if ($param->allowsNull()) {$parameters[] = null;} else {$parameters[] = false;}}}}return $parameters;}

如你所见，到目前为止我们只实现了从容器中取出实例，从哪里去提供实例定义呢，所以我们还需要提供一个方法.

    /*** @param string $id* @param string | array | callable $concrete* @throws ContainerException*/public function injection($id, $concrete){if (!is_string($id)) {throw new \InvalidArgumentException(sprintf('The id parameter must be of type string, %s given',is_object($id) ? get_class($id) : gettype($id)));}if (is_array($concrete) && !isset($concrete['class'])) {throw new ContainerException('数组必须包含类定义');}$this->definitions[$id] = $concrete;}

只有这样吗？对的，有了这些操作我们已经有一个完整的容器了，插箱即用。

不过为了使用方便，我们可以再提供一些便捷的方法，比如数组式访问。

class Container extends AbstractContainer implements \ArrayAccess
{public function offsetExists($offset){return $this->has($offset);}public function offsetGet($offset){return $this->get($offset);}public function offsetSet($offset, $value){return $this->injection($offset, $value);}public function offsetUnset($offset){unset($this->resolvedEntries[$offset]);unset($this->definitions[$offset]);}
}

这样我们就拥有了一个功能丰富，使用方便的轻量级容器了，赶快整合到你的项目中去吧。

点击这里查看完整代码