ActionDispatch::ShowExceptions - rails upgrade 2.3.x to 3.2.x

In my rails2.3.11 app/controllers/application_controller.rb I have this

ActionDispatch::ShowExceptions::rescue_responses[“ActionController::RoutingError”] = :not_found

now this feature is deprecated in rails-3.2.11, I am getting this server log

DEPRECATION WARNING: ActionDispatch::ShowExceptions.rescue_responses is deprecated. Please configure your exceptions using a railtie or in your application config instead. (called from ApplicationController at /home/app/demo/app/controllers/application_controller.rb:31)

I need specific help on How to set ActionDispatch::ShowExceptions::rescue_responses in rails3.2.11, so I can’t get deprecated warning. I am using Jruby 1.7.2 and rails 3.2.11