参考Yii2实现的以依赖注入为基础的服务定位器，Yii2代码部分为vendor/yiisoft/yii2/di/
依赖注入DI
依赖注入知道怎么初始化对象，仅仅配置构造参数就可以，核心代码如下(简化，只是说思路)
class Di
{
//经过new ReflectionClass()返回后的实例
public $_reflections = [];
//构造函数依赖关系
public $_dependencies = [];
public function build($class,$params)
{
$reflection = new ReflectionClass();
$constructor = $reflection->getConstructor();
if ($constructor !== null) {
foreach ($constructor->getParameters() as $param) {
if (version_compare(PHP_VERSION, '5.6.0', '>=') && $param->isVariadic()) {
break;
} elseif ($param->isDefaultValueAvailable()) {
$dependencies[] = $param->getDefaultValue();
} else {
$c = $param->getClass();
$dependencies[] = $c === null ? null : $c->getName();
}
}
}
$this->_reflections[$class] = $reflection;
$this->_dependencies[$class] = $dependencies;
//.... 将$params参数对应给构造函数依赖关系，简化代码
return $reflection->newInstanceArgs($params);
}
}
可以非常灵活的自定义如何new对象，如Yii2中:(如何类实现了Configurable接口，则将最后一个构造参数变成$config)
if (!empty($dependencies) && $reflection->implementsInterface('yii\base\Configurable')) {
// set $config as the last parameter (existing one will be overwritten)
$dependencies[count($dependencies) - 1] = $config;
return $reflection->newInstanceArgs($dependencies);
}
也可以(将$config依次赋予类，触发魔术方法__set)
$object = $reflection->newInstanceArgs($dependencies);
foreach ($config as $name => $value) {
$object->$name = $value;
}
还可以在应用初始化的时候，先定义好依赖关系和那些类是单例模式
class Di
{
//经过new ReflectionClass()返回后的实例
public $_reflections = [];
//经过new ReflectionClass()返回后的实例的构造函数依赖关系
public $_dependencies = [];
//映射出的容器id的类的初始化参数
private $_params = [];
//映射出的容器id与类的依赖关系
private $_definitions = [];
//那些类是被定义的单例模式
private $_singletons = [];
}
如果单单仅使用依赖注入，则其实本质还是new class_name，需要和服务定位器配合
服务定位器
服务定位器可以在应用初始化的时候定义容器id对应的类关系，还可以在应用运行时候动态修改容器id与类的映射
如一个db类，可以理解成是一个db容器，在测试环境需要连接127.0.0.1:3306,在灰度环境需要连接10.8.8.8:3386，在开发环境需要连接10.9.9.9:3307，我们可以进行如下定义，仅仅修改配置就可以让di层知道如何创建容器
$config = [
"components"=>[
"db"=> function(){
if(测试环境){
return [
"class" => "test_db",
"params" => [连接参数127.0.0.1:3306]
];
} elseif (灰度环境){
return [
"class" => "grey_db",
"params" => [连接参数10.8.8.8:3386]
];
} elseif (开发环境){
return [
"class" => "pro_db",
"params" => [连接参数10.9.9.9:3307]
];
}
}
]
];
如test.php中的代码:
<?php
use di\Application;
use di\BaseObject;
use di\DiBase;
include "./start.php";
class app extends Application
{
}
$config = [
//依赖注入容器配置
'container' => [
'definitions' => [
],
'singletons' => [
"test_obj\\B" => [
"name" => 1
],
]
],
//组件容器配置
"components" => [
"db" => [
"class"=>"test_obj\\A",
"age"=>1
],
"cache" => [
"class"=>"test_obj\\B",
"name" => 33
],
"log"=>[
"class"=>"test_obj\\C",
"age"=>1
]
]
];
$app = new app($config);
//获取一个cache服务
if($app->has("cache")){
$cache = $app->get("cache");
var_dump($cache->name);//33
}
//重新注册一个cache服务
if($app->has("cache")){
$app->set("cache",["class"=>"test_obj\\B","name"=>44]);
$cache = $app->get("cache");
var_dump($cache->name);//33 因为test_obj\\B已经被注册成了单例模式
}
//获取一个db服务，有注册属性
if($app->has("db")){
$cache = $app->get("db");
var_dump($cache->age);//注册属性的逻辑是$this->age = age + 1;
}
如定义了一个容器db（容器id是db），那么db容器对应的类就是"test_obj\A",可以在应用中动态修改这个映射，将容器的实例化转移到了DI层，也可以在初始化中修改$config配置，从而减少了容器之间的藕合
在Yii2中，容器id的映射也可以是一个回调，可以非常灵活的设置依赖关系
该模式也支持了设置依赖类属性，具体核心代码(简化)：
<?php
namespace di;
use Exception;
class BaseObject implements Configurable{
public function __construct($config = [])
{
if (!empty($config)) {
//这么做的目的就是用另一个类去设置属性，触发该类的魔术方法
DiBase::configure($this, $config);
}
$this->init();
}
public function init()
{
}
public function __get($name)
{
$getter = 'get' . $name;
if (method_exists($this, $getter)) {
return $this->$getter();
} elseif (method_exists($this, 'set' . $name)) {
throw new Exception('Getting write-only property: ' . get_class($this) . '::' . $name);
}
throw new Exception('Getting unknown property: ' . get_class($this) . '::' . $name);
}
public function __set($name, $value)
{
$setter = 'set' . $name;
if (method_exists($this, $setter)) {
$this->$setter($value);
} elseif (method_exists($this, 'get' . $name)) {
throw new Exception('Setting read-only property: ' . get_class($this) . '::' . $name);
} else {
throw new Exception('Setting unknown property: ' . get_class($this) . '::' . $name);
}
}
public function __isset($name)
{
$getter = 'get' . $name;
if (method_exists($this, $getter)) {
return $this->$getter() !== null;
}
return false;
}
public function __unset($name)
{
$setter = 'set' . $name;
if (method_exists($this, $setter)) {
$this->$setter(null);
} elseif (method_exists($this, 'get' . $name)) {
throw new Exception('Unsetting read-only property: ' . get_class($this) . '::' . $name);
}
}
public function __call($name, $params)
{
throw new Exception('Calling unknown method: ' . get_class($this) . "::$name()");
}
public function hasProperty($name, $checkVars = true)
{
return $this->canGetProperty($name, $checkVars) || $this->canSetProperty($name, false);
}
public function canGetProperty($name, $checkVars = true)
{
return method_exists($this, 'get' . $name) || $checkVars && property_exists($this, $name);
}
public function canSetProperty($name, $checkVars = true)
{
return method_exists($this, 'set' . $name) || $checkVars && property_exists($this, $name);
}
public function hasMethod($name)
{
return method_exists($this, $name);
}
}