ApplicationController中的rescue_from没有捕获异常

Question

我正在设置一个简单的RoR应用程序。它将ActiveAdmin与CanCan混合以管理授权。当我提出CanCan::AccessDenied时，异常永远不会被解除：

class ApplicationController < ActionController::Base
  # Prevent CSRF attacks by raising an exception.
  protect_from_forgery
  # Ensure authorization happens on every action in your application
  check_authorization

  # If the user authorization fails, a CanCan::AccessDenied exception will be raised
  rescue_from CanCan::AccessDenied do |exception|
    redirect_to root_url, :alert => exception.message
  end

  def access_denied!(exception)
    raise CanCan::AccessDenied.new exception.message
  end
end

不会重定向到root_url，而是显示异常，就像它没有被捕获一样。

有任何线索吗？谢谢！