How to adapt basic android service to run an activity in the background?

I want to create an android service which is able to fetch and parse JSON data into my local database. I have already written the code for this to be done as a normal activity. But I would like to change it so that it updates the database on a regular basis. How would I go about doing this?

So far I have created a basic service but I do not know how to tie in my activity into the service or how to set the service to start up when the application is opened up.

Basic Data Service

public class DataFetcher extends Service {

    private static final int POLL_PERIOD=120000;

    private AtomicBoolean active=new AtomicBoolean(true);



    @Override

    public void onCreate() {

        super.onCreate();



    }



    @Override

    public IBinder onBind(Intent intent) {

        return(null);

    }



    @Override

    public void onDestroy() {

        super.onDestroy();

    }



    private Runnable threadBody=new Runnable() {

        public void run() {

            while(active.get()) {



                SystemClock.sleep(POLL_PERIOD);

            }

        }

    };

}