writeexcel_template_handler.rb

require 'action_dispatch/http/mime_type'
require 'action_view'
require 'active_support'
require 'writeexcel'

class WriteExcelTemplateHandler
  def self.call(template)
    %{
      tmp = Tempfile.new('writeexcel')
      workbook = WriteExcel.new(tmp.path)
      #{template.source}
      workbook.close
      tmp.read
    }
  end
end

Mime::Type.register('application/vnd.ms-excel', :xls)
::ActionView::Template.register_template_handler('writeexcel', WriteExcelTemplateHandler)

Rails 3.1+ compatibility.