Laravel的Controller主要提供filter的功能。
值得一提的是，在執行工作：Routing/Route.php裏面我們看到，Route類別有變數去儲存before與after等filter動作。然而此處的Controller類別又有beforeFilters與afterFilters去儲存filter動作。
這樣的設計允許了filter的兩種寫法：一種是在設定routes規則時撰寫、一種是寫在controller內。參見官網「Controller Filters」一節的舉例。

beforeFilters[] = $this->parseFilter($filter, $options);
	}

	/**
	 * Register an "after" filter on the controller.
	 *
	 * @param  \Closure|string  $filter
	 * @param  array  $options
	 * @return void
	 */
	public function afterFilter($filter, array $options = array())
	{
		$this->afterFilters[] = $this->parseFilter($filter, $options);
	}

	/**
	 * Parse the given filter and options.
	 *
	 * @param  \Closure|string  $filter
	 * @param  array  $options
	 * @return array
	 */
	protected function parseFilter($filter, array $options)
	{
		$parameters = array();

		$original = $filter;

		if ($filter instanceof Closure)
		{
			$filter = $this->registerClosureFilter($filter);
		}
		elseif ($this->isInstanceFilter($filter))
		{
			$filter = $this->registerInstanceFilter($filter);
		}
		else
		{
			list($filter, $parameters) = Route::parseFilter($filter);
		}

		return compact('original', 'filter', 'parameters', 'options');
	}

	/**
	 * Register an anonymous controller filter Closure.
	 *
	 * @param  \Closure  $filter
	 * @return string
	 */
	protected function registerClosureFilter(Closure $filter)
	{
		$this->getFilterer()->filter($name = spl_object_hash($filter), $filter);

		return $name;
	}

	/**
	 * Register a controller instance method as a filter.
	 *
	 * @param  string  $filter
	 * @return string
	 */
	protected function registerInstanceFilter($filter)
	{
		$this->getFilterer()->filter($filter, array($this, substr($filter, 1)));

		return $filter;
	}

	/**
	 * Determine if a filter is a local method on the controller.
	 *
	 * @param  mixed  $filter
	 * @return boolean
	 *
	 * @throws \InvalidArgumentException
	 */
	protected function isInstanceFilter($filter)
	{
		if (is_string($filter) && starts_with($filter, '@'))
		{
			if (method_exists($this, substr($filter, 1))) return true;

			throw new \InvalidArgumentException("Filter method [$filter] does not exist.");
		}

		return false;
	}

	/**
	 * Remove the given before filter.
	 *
	 * @param  string  $filter
	 * @return void
	 */
	public function forgetBeforeFilter($filter)
	{
		$this->beforeFilters = $this->removeFilter($filter, $this->getBeforeFilters());
	}

	/**
	 * Remove the given after filter.
	 *
	 * @param  string  $filter
	 * @return void
	 */
	public function forgetAfterFilter($filter)
	{
		$this->afterFilters = $this->removeFilter($filter, $this->getAfterFilters());
	}

	/**
	 * Remove the given controller filter from the provided filter array.
	 *
	 * @param  string  $removing
	 * @param  array  $current
	 * @return array
	 */
	protected function removeFilter($removing, $current)
	{
		return array_filter($current, function($filter) use ($removing)
		{
			return $filter['original'] != $removing;
		});
	}

	/**
	 * Get the registered "before" filters.
	 *
	 * @return array
	 */
	public function getBeforeFilters()
	{
		return $this->beforeFilters;
	}

	/**
	 * Get the registered "after" filters.
	 *
	 * @return array
	 */
	public function getAfterFilters()
	{
		return $this->afterFilters;
	}

	/**
	 * Get the route filterer implementation.
	 *
	 * @return \Illuminate\Routing\RouteFiltererInterface
	 */
	public static function getFilterer()
	{
		return static::$filterer;
	}

	/**
	 * Set the route filterer implementation.
	 *
	 * @param  \Illuminate\Routing\RouteFiltererInterface  $filterer
	 * @return void
	 */
	public static function setFilterer(RouteFiltererInterface $filterer)
	{
		static::$filterer = $filterer;
	}

	/**
	 * Create the layout used by the controller.
	 *
	 * @return void
	 */
	protected function setupLayout() {}

	/**
	 * Execute an action on the controller.
	 *
	 * @param  string  $method
	 * @param  array   $parameters
	 * @return \Symfony\Component\HttpFoundation\Response
	 */
	public function callAction($method, $parameters)
	{
		$this->setupLayout();

		$response = call_user_func_array(array($this, $method), $parameters);

		// If no response is returned from the controller action and a layout is being
		// used we will assume we want to just return the layout view as any nested
		// views were probably bound on this view during this controller actions.
		if (is_null($response) && ! is_null($this->layout))
		{
			$response = $this->layout;
		}

		return $response;
	}

	/**
	 * Handle calls to missing methods on the controller.
	 *
	 * @param  array   $parameters
	 * @return mixed
	 *
	 * @throws \Symfony\Component\HttpKernel\Exception\NotFoundHttpException
	 */
	public function missingMethod($parameters = array())
	{
		throw new NotFoundHttpException("Controller method not found.");
	}

	/**
	 * Handle calls to missing methods on the controller.
	 *
	 * @param  string  $method
	 * @param  array   $parameters
	 * @return mixed
	 *
	 * @throws \BadMethodCallException
	 */
	public function __call($method, $parameters)
	{
		throw new \BadMethodCallException("Method [$method] does not exist.");
	}

}