class MyCustomError < StandardError; end

class PostsController < ApplicationController

  rescue_from(MyCustomError) do |error|
    logger.info error.message
  end

  assume(:post) { raise MyCustomError.new('Caught by #rescue_from') }

  def show
    respond_to do |format|
      format.html
      format.xml  { render :xml => post }
    end
  end

end