Android post json to API in background

i have two applications, i have the android app and the Ruby on Rails API. In android i have a SQLite database and almost all the time i need sync the android database with the API database, but this synchronization can take a "long time", something like 10 seconds if is the first sync, so user need to keep waiting and looking to load screen until the process done.

So, i want send a post to the Ruby on Rails application, but without "stop" the application in the load screen, i want to do this sync in background, so the user wont realise that the app is syncing with the API.

Now, i'm trying to working with threads, but it still fails.

Thanks.

via Chebli Mohamed