laravel框架的中间件middleware的详解 - it-world

来源：cnblogs　　作者：it-world　　时间：2019/11/5 10:32:39　　对本文有异议

本篇文章给大家带来的内容是关于laravel框架的中间件middleware的详解，有一定的参考价值，有需要的朋友可以参考一下，希望对你有所帮助。

laravel中间件是个非常方便的东西，能将一些逻辑实现解耦，并且在laravel中，
中间件的编写也是非常的方便。谁用谁知道。

1.装饰器模式

laravel中的中间件使用的就是装饰器模式，什么是[装饰器模式][1]，先去了解一下吧，这里大概说一下，就是这个模式主要的就是用于解决当一个类需要动态扩展功能的时候，使用继承的方式会让子类膨胀，并且这个扩展的功能是个公用功能的情况下，不利于功能的复用以及代码的解耦。

在laravel，使用对于使用这种模式的功能，称为请求处理管道，也就是pipeline

//公共接口
interface middleware {
        public static function handle(Closure $next);
    }
//装饰器1
class MiddleStepOne implements middleware{
        public static function handle(Closure $next) {
            echo "前期处理的第一步"."<br>";
            $next();
            echo "后期处理的第一步"."<br>";
        }
    }
//装饰器2
class MiddleStepTwo implements middleware{
    public static function handle(Closure $next) {
        echo "前期处理的第二步"."<br>";
        $next();
        echo "后期处理的第二步"."<br>";
    }
}
 
function goFunc() {
    return function ($step,$className) {
      return function () use ($step,$className) {
          return $className::handle($step);
      };
    };
}
 
$pip = array(
    MiddleStepOne::class,
    MiddleStepTwo::class,
);
$pip = array_reverse($pip);  //反转数组，以求达到要求的顺序运行
$first = function (){
    echo "前期处理完毕"."<br>";
};  //实际要处理的函数
$a = array_reduce($pip,goFunc(),$first); //遍历pip数组，并将first作为第一个参数传递进去
$a(); //执行

输出：

这个就是一个简单的基于装饰器模式的管道。他的本质其实就是基于闭包和递归。

通过分析这个程序，对于最终生成的$a变量，它的值大概是这样的 MiddleStepOne.handle(MiddleStepTwo.handle(first))，当执行的时候因为在handle中有个next()函数的存在，所以这是一个递归的调用。对于laravel的中间件，他的实现原理也是和这个一样的。

2.laravel中的中间件和请求处理管道

在laravel中，我们我们可以通过设置中间件来在请求执行之前做一些预先的处理。

从请求入口 public/index.php开始

重要的是这段代码：即处理请求，返回请求的响应

$response = $kernel->handle(
$request = Illuminate\Http\Request::capture() //创建一个请求实例
);

接着我们进入kernel中看他的具体实现 IlluminateFoundationHttpKernel.php中

关于dispatchToRouter()函数请大家自己去看，这里就不多说了。

接下来就是激动人心的PipeLine类了，

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<?php
 
namespace Illuminate\Pipeline;
 
use Closure;
use RuntimeException;
use Illuminate\Contracts\Container\Container;
use Illuminate\Contracts\Pipeline\Pipeline as PipelineContract;
 
class Pipeline implements PipelineContract
{
    /**
     * The container implementation.
     *
     * @var \Illuminate\Contracts\Container\Container
     */
    protected $container;
 
    /**
     * The object being passed through the pipeline.
     *
     * @var mixed
     */
    protected $passable;
 
    /**
     * The array of class pipes.
     *
     * @var array
     */
    protected $pipes = [];
 
    /**
     * The method to call on each pipe.
     *
     * @var string
     */
    protected $method = 'handle';
 
    /**
     * Create a new class instance.
     *
     * @param  \Illuminate\Contracts\Container\Container|null  $container
     * @return void
     */
    public function __construct(Container $container = null)
    {
        $this->container = $container;
    }
 
    /**
     * Set the object being sent through the pipeline.
     *
     * @param  mixed  $passable
     * @return $this
     */
    public function send($passable)
    {
        $this->passable = $passable;
 
        return $this;
    }
 
    /**
     * Set the array of pipes.
     *
     * @param  array|mixed  $pipes
     * @return $this
     */
    public function through($pipes)
    {
        $this->pipes = is_array($pipes) ? $pipes : func_get_args();
 
        return $this;
    }
 
    /**
     * Set the method to call on the pipes.
     *
     * @param  string  $method
     * @return $this
     */
    public function via($method)
    {
        $this->method = $method;
 
        return $this;
    }
 
    /**
     * Run the pipeline with a final destination callback.
     *
     * @param  \Closure  $destination
     * @return mixed
     */
    public function then(Closure $destination)
    {
        $pipeline = array_reduce(
            array_reverse($this->pipes), $this->carry(), $this->prepareDestination($destination)
        );
 
        return $pipeline($this->passable);
    }
 
    /**
     * Get the final piece of the Closure onion.
     *
     * @param  \Closure  $destination
     * @return \Closure
     */
    protected function prepareDestination(Closure $destination)
    {
        return function ($passable) use ($destination) {
            return $destination($passable);
        };
    }
 
    /**
     * Get a Closure that represents a slice of the application onion.
     *
     * @return \Closure
     */
    protected function carry()
    {
        return function ($stack, $pipe) {
            return function ($passable) use ($stack, $pipe) {
                if (is_callable($pipe)) {
                    // If the pipe is an instance of a Closure, we will just call it directly but
                    // otherwise we'll resolve the pipes out of the container and call it with
                    // the appropriate method and arguments, returning the results back out.
                    //如果pip也就中间件函数是一个闭包可调用函数，就直接返回这个闭包函数就行了
                    //这里我还没有找到对应的使用场景，后续补充
                    return $pipe($passable, $stack);
                } elseif (! is_object($pipe)) {
                    list($name, $parameters) = $this->parsePipeString($pipe);
 
                    // If the pipe is a string we will parse the string and resolve the class out
                    // of the dependency injection container. We can then build a callable and
                    // execute the pipe function giving in the parameters that are required.
                    $pipe = $this->getContainer()->make($name);
 
                    $parameters = array_merge([$passable, $stack], $parameters);
                } else {
                    // If the pipe is already an object we'll just make a callable and pass it to
                    // the pipe as-is. There is no need to do any extra parsing and formatting
                    // since the object we're given was already a fully instantiated object.
                    $parameters = [$passable, $stack];
                }
 
                return method_exists($pipe, $this->method)
                                ? $pipe->{$this->method}(...$parameters)
                                : $pipe(...$parameters);
            };
        };
    }
 
    /**
     * Parse full pipe string to get name and parameters.
     *
     * @param  string $pipe
     * @return array
     */
    protected function parsePipeString($pipe)
    {
        list($name, $parameters) = array_pad(explode(':', $pipe, 2), 2, []);
 
        if (is_string($parameters)) {
            $parameters = explode(',', $parameters);
        }
 
        return [$name, $parameters];
    }
 
    /**
     * Get the container instance.
     *
     * @return \Illuminate\Contracts\Container\Container
     * @throws \RuntimeException
     */
    protected function getContainer()
    {
        if (! $this->container) {
            throw new RuntimeException('A container instance has not been passed to the Pipeline.');
        }
 
        return $this->container;
    }
}