richpeck/application.rb

## application.rb
# config/application.rb
# This can be put in any of the "environment" files - config/application.rb is just the main
config.exceptions_app = ->(env) { ApplicationController.action(:exception).call(env) }

# If you want custom exceptions, you need to add new rescue_responses:
# http://guides.rubyonrails.org/configuring.html#configuring-action-dispatch
config.action_dispatch.rescue_response["Your::Exception"] = :bad_request

## application_controller.rb
# app/controllers/exceptions_controller.rb
# This takes the exception request and returns the "show" view
class ApplicationController < ApplicationController

  ######################################
  ######################################

    # => Exception
    # => Set the @exception object
    # => Since we've received the request, we can do what we want here
    def exception
      @exception  = env['action_dispatch.exception']
      @status     = ActionDispatch::ExceptionWrapper.new(env, @exception).status_code
      @message    = ActionDispatch::ExceptionWrapper.rescue_responses[@exception.class.name]

      render :exception, status: @status, layout: ("exception" if @status == 500)
    end

  ######################################
  ######################################

end

## exception.html.erb
# app/views/application/exception.html.erb
# Exception view
# This will remain constant for all erroneous responses, allowing us to change the layout only
<h1> Error <%= @status %></h1>
<p><%= @message %></p>

## exception.html.erb_
# app/views/layouts/exception.html.erb
# Exception layout designed to give you a 500 error page layout with no conflicts
<html>
  <head>
     <title><%= @status %> Error</title>
     <%= stylesheet_include_tag :application # - you can include any CSS you want %>
  </head>
  <body>
    <%= @message %>
  </body>
</html>
	# config/application.rb
	# This can be put in any of the "environment" files - config/application.rb is just the main
	config.exceptions_app = ->(env) { ApplicationController.action(:exception).call(env) }

	# If you want custom exceptions, you need to add new rescue_responses:
	# http://guides.rubyonrails.org/configuring.html#configuring-action-dispatch
	config.action_dispatch.rescue_response["Your::Exception"] = :bad_request
	# app/controllers/exceptions_controller.rb
	# This takes the exception request and returns the "show" view
	class ApplicationController < ApplicationController

	######################################
	######################################

	# => Exception
	# => Set the @exception object
	# => Since we've received the request, we can do what we want here
	def exception
	@exception = env['action_dispatch.exception']
	@status = ActionDispatch::ExceptionWrapper.new(env, @exception).status_code
	@message = ActionDispatch::ExceptionWrapper.rescue_responses[@exception.class.name]

	render :exception, status: @status, layout: ("exception" if @status == 500)
	end

	######################################
	######################################

	end
	# app/views/application/exception.html.erb
	# Exception view
	# This will remain constant for all erroneous responses, allowing us to change the layout only
	<h1> Error <%= @status %></h1>
	<p><%= @message %></p>
	# app/views/layouts/exception.html.erb
	# Exception layout designed to give you a 500 error page layout with no conflicts
	<html>
	<head>
	<title><%= @status %> Error</title>
	<%= stylesheet_include_tag :application # - you can include any CSS you want %>
	</head>
	<body>
	<%= @message %>
	</body>
	</html>