Integrate Dropbox with you Rails Application by using Dropbox API gem with Paperclip, (http://sreeharikmarar.blogspot.in/2013/07/ruby-on-rails-practice-some-safe.html)

dropbox_controller.rb

class DropboxController < ApplicationController
  def authorize
    consumer = Dropbox::API::OAuth.consumer(:authorize)
    request_token = consumer.get_request_token
    session[:request_token] = request_token.token
    session[:request_token_secret] = request_token.secret

    redirect_to request_token.authorize_url(:oauth_callback => "http://#{request.host_with_port}/dropbox/callback")

  end

  def callback
    consumer = Dropbox::API::OAuth.consumer(:authorize)
    request_token = OAuth::RequestToken.new(consumer, session[:request_token], session[:request_token_secret])
    access_token = request_token.get_access_token(:oauth_verifier => params[:oauth_token])
    session[:access_token]  = access_token.token
    session[:secret_token] = access_token.secret

    @client = Dropbox::API::Client.new :token => session[:access_token], :secret => session[:secret_token]
    
    if @client.ls.any?
      @client.ls.each do |f|
        directory_hash(f)
      end
    end
    
  end

  private

  def directory_hash(obj)
    if obj.is_dir?
      list_hash(obj)
    else
      download_and_create(obj)
    end
  end
  
  def list_hash(obj)
    obj.ls.each do |s|
      directory_hash(s)
    end
  end
  
  def download_and_create(obj)
    path = download_file_from_url(obj)
    dp_file = File.open(path) if File.exists?(path)
    if dp_file
      DropboxFiles.create(:document => dp_file)
      File.delete(dp_file)
    end
  end
  
  def download_file_from_url(obj)
    destination_file_full_path = Rails.root.to_s + "/" + obj.path.to_s.split("/").last
    begin
      open(destination_file_full_path, 'wb') do |file|
        file << open(obj.direct_url.url).read
      end
    rescue
      puts "Exception occured while downloading..."
    end
    destination_file_full_path
  end
  
end