uninitialized constant HelloMessageController::HelloMessageApi

[Magudamudi]

Hi,
I practice some examples but i couldn't run it well

hello_message_controller.rb:

 
class HelloMessageController < ApplicationController
 
  web_service_api HelloMessageApi
    wsdl_service_name 'hello_message'
        web_service_scaffold :invoke
 
  def hello_message(firstname, lastname)
    return "Hello" + firstname+" "+lastname
  end
 
end
 
 

Hello_message_api.rb:

 
class HelloMessageApi < ActionWebService::API::Base
  api_method :hello_message, expects => [{:firstname=>:string},
    {:lastname=>string}], :returns=>[:string]
end
 
 

when i open localhost:3000/hello_message/invoke
i got the following error:

NameError in Hello messageController#invoke

uninitialized constant HelloMessageController::HelloMessageApi

Any one help me why this error occur and how can we overcome this error?

Thanks in Advance!