摘要：實(shí)際上的綁定主要有三種方式且只是一種的，這些已經(jīng)在學(xué)習(xí)筆記之實(shí)例化源碼解析聊過，其實(shí)現(xiàn)方法并不復(fù)雜。從以上源碼發(fā)現(xiàn)的反射是個(gè)很好用的技術(shù)，這里給出個(gè)，看下能干些啥打印結(jié)果太長了，就不粘貼了。

說明：本文主要學(xué)習(xí)Laravel中Container的源碼，主要學(xué)習(xí)Container的綁定和解析過程，和解析過程中的依賴解決。分享自己的研究心得，希望對(duì)別人有所幫助。實(shí)際上Container的綁定主要有三種方式：bind(),singleton(),instance(),且singleton()只是一種"shared" = true的bind()，這些已經(jīng)在Laravel學(xué)習(xí)筆記之IoC Container實(shí)例化源碼解析聊過，其實(shí)現(xiàn)方法并不復(fù)雜。當(dāng)Service通過Service Provider綁定到Container中后，當(dāng)需要該Service時(shí)，是需要Container幫助自動(dòng)解析make()。OK,下面聊聊自動(dòng)解析過程，研究下Container是如何在自動(dòng)解析Service時(shí)解決該Service的依賴問題的。

開發(fā)環(huán)境： Laravel5.3 + PHP7 + OS X 10.11

在聊解析過程前，先測試下IlluminateContainerContainer中綁定的源碼，這里測試下bind(),singleton(),instance()三個(gè)綁定方式：

container = new Container();
    }

    public function testBindClosure()
    {
        // Arrange
        $expected = "Laravel is a PHP Framework.";
        $this->container->bind("PHP", function () use ($expected) {
            return $expected;
        });

        // Actual
        $actual = $this->container->make("PHP");

        // Assert
        $this->assertEquals($expected, $actual);
    }

    public function testBindInterfaceToImplement()
    {
        // Arrange
        $this->container->bind(IContainerStub::class, ContainerImplementationStub::class);

        // Actual
        $actual = $this->container->make(IContainerStub::class);

        // Assert
        $this->assertInstanceOf(IContainerStub::class, $actual);
    }

    public function testBindDependencyResolution()
    {
        // Arrange
        $this->container->bind(IContainerStub::class, ContainerImplementationStub::class);

        // Actual
        $actual = $this->container->make(ContainerNestedDependentStub::class);

        // Assert
        $this->assertInstanceOf(ContainerDependentStub::class, $actual->containerDependentStub);
        $this->assertInstanceOf(ContainerImplementationStub::class, $actual->containerDependentStub->containerStub);
    }

    public function testSingleton()
    {
        // Arrange
        $this->container->singleton(ContainerConcreteStub::class);
        $expected = $this->container->make(ContainerConcreteStub::class);

        // Actual
        $actual = $this->container->make(ContainerConcreteStub::class);

        // Assert
        $this->assertSame($expected, $actual);
    }

    public function testInstanceExistingObject()
    {
        // Arrange
        $expected = new ContainerImplementationStub();
        $this->container->instance(IContainerStub::class, $expected);

        // Actual
        $actual = $this->container->make(IContainerStub::class);

        // Assert
        $this->assertSame($expected, $actual);
    }
}

class ContainerConcreteStub
{

}

interface IContainerStub
{

}

class ContainerImplementationStub implements IContainerStub
{

}

class ContainerDependentStub
{
    /**
     * @var MyRightCapitalContainerTestsIContainerStub
     */
    public $containerStub;

    public function __construct(IContainerStub $containerStub)
    {
        $this->containerStub = $containerStub;
    }
}

class ContainerNestedDependentStub
{
    /**
     * @var MyRightCapitalContainerTestsContainerDependentStub
     */
    public $containerDependentStub;

    public function __construct(ContainerDependentStub $containerDependentStub)
    {
        $this->containerDependentStub = $containerDependentStub;
    }
}

這里測試了bind()綁定閉包，綁定接口和對(duì)應(yīng)實(shí)現(xiàn)，依賴解析這三個(gè)feature，singleton()測試了是否為單例綁定一個(gè)feature，instance()測試了已存在對(duì)象綁定這個(gè)feature，測試結(jié)果5個(gè)tests都通過：

關(guān)于在PHPStorm中配置PHPUnit可參考這篇：Laravel學(xué)習(xí)筆記之基于PHPStorm編輯器的Laravel開發(fā)

從以上testcase知道，make()是負(fù)責(zé)從Container中解析出service的，而且在testBindDependencyResolution()這個(gè)test中，還能發(fā)現(xiàn)當(dāng)ContainerNestedDependentStub::class有構(gòu)造依賴時(shí)，Container也會(huì)自動(dòng)去解析這個(gè)依賴并注入ContainerNestedDependentStub::class的構(gòu)造函數(shù)中，這個(gè)依賴是ContainerDependentStub::class，而這個(gè)依賴又有自己的依賴IContainerStub::class，從斷言語句$this->assertInstanceOf(ContainerImplementationStub::class, $actual->containerDependentStub->containerStub);知道，Container又自動(dòng)解析了這個(gè)依賴，所有這一切都不需要我們手動(dòng)去解析，全都是Container自動(dòng)化解析的。

這一切Container是怎么做到的？
實(shí)際上并不復(fù)雜，解決依賴只是用了PHP的Reflector反射機(jī)制來實(shí)現(xiàn)的。先看下make()源碼：

    /**
     * Resolve the given type from the container.
     *
     * @param  string  $abstract
     * @param  array   $parameters
     * @return mixed
     */
    public function make($abstract, array $parameters = [])
    {
        $abstract = $this->getAlias($this->normalize($abstract));

        // 如果是instance()綁定的方式，就直接解析返回綁定的service
        if (isset($this->instances[$abstract])) {
            return $this->instances[$abstract];
        }

        // 獲取$abstract對(duì)應(yīng)綁定的$concrete
        $concrete = $this->getConcrete($abstract);

        if ($this->isBuildable($concrete, $abstract)) {
            $object = $this->build($concrete, $parameters);
        } else {
            $object = $this->make($concrete, $parameters);
        }

        foreach ($this->getExtenders($abstract) as $extender) {
            $object = $extender($object, $this);
        }

        if ($this->isShared($abstract)) {
            $this->instances[$abstract] = $object;
        }

        $this->fireResolvingCallbacks($abstract, $object);

        $this->resolved[$abstract] = true;

        return $object;
    }
    
    protected function getConcrete($abstract)
    {
        if (! is_null($concrete = $this->getContextualConcrete($abstract))) {
            return $concrete;
        }

        // 如果是$this->container->singleton(ContainerConcreteStub::class);這種方式綁定，即$concrete = null
        // 則 $abstract = $concrete，可看以上PHPUnit的testSingleton()這個(gè)test
        // 這種方式稱為"自動(dòng)補(bǔ)全"綁定
        if (! isset($this->bindings[$abstract])) {
            return $abstract;
        }

        return $this->bindings[$abstract]["concrete"];
    }
    
    protected function isBuildable($concrete, $abstract)
    {
        return $concrete === $abstract || $concrete instanceof Closure;
    }

從以上源碼可知道如果綁定的是閉包或者"自動(dòng)補(bǔ)全"綁定($concrete = null)，則需要build()這個(gè)閉包或類名，轉(zhuǎn)換成對(duì)應(yīng)的實(shí)例。如果是"接口實(shí)現(xiàn)"這種方式綁定，則需要再一次調(diào)用make()并經(jīng)過getConcrete后$abstract = $concrete，然后符合isBuildable()的條件，進(jìn)入build()函數(shù)內(nèi)。所以以上的PHPUnit的測試用例中不管什么方式的綁定，都要進(jìn)入build()函數(shù)內(nèi)編譯出相應(yīng)對(duì)象實(shí)例。當(dāng)編譯出對(duì)象后，檢查是否是共享的，以及是否要觸發(fā)回調(diào)，以及標(biāo)記該對(duì)象已經(jīng)被解析。OK，看下build()的源碼：

    /**
     * Instantiate a concrete instance of the given type.
     *
     * @param  string  $concrete
     * @param  array   $parameters
     * @return mixed
     *
     * @throws IlluminateContractsContainerBindingResolutionException
     */
    public function build($concrete, array $parameters = [])
    {
        // 如果是閉包直接執(zhí)行閉包并返回，e.g. PHPUnit的這個(gè)test:testBindClosure()
        if ($concrete instanceof Closure) {
            return $concrete($this, $parameters);
        }
        
        // 如這個(gè)test:testBindInterfaceToImplement()，這里的$concrete = ContainerImplementationStub::class類名稱，
        // 則使用反射ReflectionClass來探測ContainerImplementationStub這個(gè)類的構(gòu)造函數(shù)和構(gòu)造函數(shù)的依賴
        $reflector = new ReflectionClass($concrete);

        // 如果ContainerImplementationStub不能實(shí)例化，這應(yīng)該是接口或抽象類，再或者就是ContainerImplementationStub的構(gòu)造函數(shù)是private的
        if (! $reflector->isInstantiable()) {
            if (! empty($this->buildStack)) {
                $previous = implode(", ", $this->buildStack);

                $message = "Target [$concrete] is not instantiable while building [$previous].";
            } else {
                $message = "Target [$concrete] is not instantiable.";
            }

            throw new BindingResolutionException($message);
        }

        $this->buildStack[] = $concrete;

        // 獲取構(gòu)造函數(shù)的反射
        $constructor = $reflector->getConstructor();

        // 如果構(gòu)造函數(shù)是空，說明沒有任何依賴，直接new返回
        if (is_null($constructor)) {
            array_pop($this->buildStack);

            return new $concrete;
        }
        
        // 獲取構(gòu)造函數(shù)的依賴，返回ReflectionParameter[]
        $dependencies = $constructor->getParameters();

        $parameters = $this->keyParametersByArgument(
            $dependencies, $parameters
        );

        // 然后就是獲取相關(guān)依賴，如testBindDependencyResolution()這個(gè)test中，
        // ContainerNestedDependentStub::class是依賴于ContainerDependentStub::class的
        $instances = $this->getDependencies(
            $dependencies, $parameters
        );

        array_pop($this->buildStack);

        return $reflector->newInstanceArgs($instances);
    }

從源碼可知道，比較麻煩的是當(dāng)ContainerNestedDependentStub::class的構(gòu)造函數(shù)有依賴ContainerDependentStub::class時(shí)，通過getDependencies()來解決的，看下getDependencies()的源碼：

    // 這里$parameters = ReflectionParameter[]
    protected function getDependencies(array $parameters, array $primitives = [])
    {
        $dependencies = [];

        foreach ($parameters as $parameter) {
            $dependency = $parameter->getClass();

            // 如果某一依賴值已給，就賦值
            if (array_key_exists($parameter->name, $primitives)) {
                $dependencies[] = $primitives[$parameter->name];
            } 
            // 如果類名為null，說明是基本類型，如"int","string" and so on.
            elseif (is_null($dependency)) {
                $dependencies[] = $this->resolveNonClass($parameter);
            } 
            // 如果是類名，如ContainerDependentStub::class，則resolveClass去解析成對(duì)象
            else {
                $dependencies[] = $this->resolveClass($parameter);
            }
        }

        return $dependencies;
    }

通過上面注釋，看下resolveClass()的源碼：

    protected function resolveClass(ReflectionParameter $parameter)
    {
        try {
            // $parameter->getClass()->name返回的是類名，如ContainerNestedDependentStub依賴于$containerDependentStub
            // $containerDependentStub的typehint是ContainerDependentStub，所以類名是"ContainerDependentStub"
            // 然后遞歸繼續(xù)make(ContainerDependentStub::class)
            // 又和PHPUnit中這個(gè)測試$this->container->make(ContainerNestedDependentStub::class)相類似了
            // ContainerNestedDependentStub又依賴于IContainerStub::class，
            // IContainerStub::class是綁定于ContainerImplementationStub::class
            // 直到ContainerImplementationStub沒有依賴或者是構(gòu)造函數(shù)是基本屬性，
            // 最后build()結(jié)束
            return $this->make($parameter->getClass()->name);
        } catch (BindingResolutionException $e) {
            if ($parameter->isOptional()) {
                return $parameter->getDefaultValue();
            }

            throw $e;
        }
    }

從以上代碼注釋直到build()是個(gè)遞歸過程，A類依賴于B類,B類依賴于C類和D類，那就從A類開始build，發(fā)現(xiàn)依賴于B類，再從Container中解析make()即再build()出B類，發(fā)現(xiàn)依賴于C類，再make() and build()，發(fā)現(xiàn)B類又同時(shí)依賴于D類，再make() and build()，以此類推直到?jīng)]有依賴或依賴基本屬性，解析結(jié)束。這樣一步步解析完后，發(fā)現(xiàn)Container的解析make()并不是很神秘很復(fù)雜中的過程。

從以上源碼發(fā)現(xiàn)PHP的反射Reflector是個(gè)很好用的技術(shù)，這里給出個(gè)test，看下Reflector能干些啥：

request = $request;
    }

    private function reflectorMethod1()
    {
    }

    protected function reflectorMethod2()
    {
    }

    public function reflectorMethod3()
    {
    }
}

$reflector_class        = new ReflectionClass(ReflectorTest::class);
$methods                = $reflector_class->getMethods();
$properties             = $reflector_class->getProperties();
$constructor            = $reflector_class->getConstructor();
$constructor_parameters = $constructor->getParameters();

foreach ($constructor_parameters as $constructor_parameter) {
    $dependency = $constructor_parameter->getClass();
    var_dump($dependency);

    if ($constructor_parameter->isDefaultValueAvailable()) {
        var_dump($constructor_parameter->getDefaultValue());
    }
}

var_dump($methods);
var_dump($properties);
var_dump($constructor);
var_dump($constructor_parameters);

打印結(jié)果太長了，就不粘貼了。可以看下PHP官方文檔：Reflector

總結(jié)：本文學(xué)習(xí)了下Container的核心功能：service resolve的過程，并學(xué)習(xí)了service的依賴是如何被自動(dòng)解析的。遇到好的心得再分享，到時(shí)見。

歡迎關(guān)注Laravel-China。

RightCapital招聘Laravel DevOps