How do I expose data in a JSON format through a web service using Rails?

class Contact < ActiveRecord::Base
  ...
end

map.resources :contacts

class ContactsController < ApplicationController
  ...
  def show
    @contact = Contact.find(params[:id]

    respond_to do |format|
      format.html
      format.xml {render :xml => @contact}
      format.js  {render :json => @contact.json}
    end
  end
  ...
end

/contacts/1 # Responds with regular html page

/contacts/1.xml # Responds with xml output of Contact.find(1) and its attributes

/contacts/1.js # Responds with json output of Contact.find(1) and its attributes