client.rb

class Client < Android::OS::AsyncTask
  def doInBackground(params)
    url = Java::Net::URL.new("http://www.bom.gov.au/fwo/IDN60901/IDN60901.94768.json")
    reader = Java::IO::BufferedReader.new(Java::IO::InputStreamReader.new(url.openStream))
    builder = Java::Lang::StringBuilder.new("")

    while ((line = reader.readLine()) != nil) do
      builder.append(line)
    end
    puts builder.toString
    reader.close
  end
end

main_activity.rb

class MainActivity < Android::App::Activity
  def onCreate(savedInstanceState)
    super
    @content_layout = Android::Widget::FrameLayout.new(self)
    @content_layout.setId(Android::View::View.generateViewId)
    @content_layout.backgroundColor = Android::Graphics::Color.parseColor("#FF0099CC")

    client = Client.new
    client.execute({})

    self.setContentView(@content_layout)
  end
end