什么是容器
在開發過程中,經常會用到的一個概率就是依賴注入。我們借助依懶注入來解耦代碼,選擇性的按需加載服務,而這些通常都是借助容器來實現。
容器實現對類的統一管理,并且確保對象實例的唯一性
常用的容器網上有很多,如 PHP-DI 、 YII-DI 等各種實現,通常他們要么大而全,要么高度適配特定業務,與實際需要存在沖突。
出于需要,我們自己造一個輕量級的輪子,為了保持規范,我們基于 PSR-11 來實現。
PSR-11
PSR 是 php-fig 提供的標準建議,雖然不是官方組織,但是得到廣泛認可。PSR-11 提供了容器接口。他包含 ContainerInterface 和 兩個異常接口,提供使用建議。
/** * 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); }
實現示例
我們先來實現接口中要求的兩個方法
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]); }
實際我們容器中注入的對象是多種多樣的,所以我們單獨抽出實例化方法。
public function make($name)
{
if (!is_string($name)) {
throw new \InvalidArgumentException(sprintf(
'The name parameter must be of type string, %s given',
is_object($name) ? get_class($name) : gettype($name)
));
}
if (isset($this->resolvedEntries[$name])) {
return $this->resolvedEntries[$name];
}
if (!$this->has($name)) {
throw new NotFoundException("No entry or class found for {$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;
}
/**
*
* 獲取構造類相關參數的依賴
* @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;
}
如你所見,到目前為止我們只實現了從容器中取出實例,從哪里去提供實例定義呢,所以我們還需要提供一個方水法
/**
* @param string $id
* @param string | array | callable $concrete
* @throws ContainerException
*/
public function injection($id, $concrete)
{
if (is_array($concrete) && !isset($concrete['class'])) {
throw new ContainerException('數組必須包含類定義');
}
$this->definitions[$id] = $concrete;
}
只有這樣嗎?對的,有了這些操作我們已經有一個完整的容器了,插箱即用。
不過為了使用方便,我們可以再提供一些便捷的方法,比如數組式訪問。
class Container extends AbstractContainer implements \ArrayAccess { public function offsetExists($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]); } }
這樣我們就擁有了一個功能豐富,使用方便的輕量級容器了。
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