merb callbacks equivalent in RAILS

Is there rails equivalents for :

Merb::BootLoader.after_app_loads
Merb::BootLoader.before_app_loads

Merb::Assets::JavascriptAssetBundler.add_callback
Merb::Assets::StylesheetAssetBundler.add_callback

Thanks,

• before_app_loads: i guess preinitializer.rb is what you are after.
• after_app_loads: is this how to use an after-initializer callback

About the other, i am not sure.