在开发过程中,经常会用到的一个概率就是依赖注入。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。
常用的容器网上有很多,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 是 php-fig 提供的标准建议,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。他包含 ContainerInterface 和 两个异常接口,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。
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;
}
/**
*
* 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('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。