Android : How to do gps tracking of other mobile

I am working on app in which smooth GPS tracking of friend's mobile can possible.

I know following way

Friend's App will have service in background which will store his current location on server in 2 or 5 second interval

On other hand who wants to track friend's location will get location list from that server.

Is there any service who provides this functionality? Is there any other idea? Please suggest.