What to use to make a synchronization logger

I have an app that synchronizes data with an online bank (Bidirectional) I'm developing a Logger for a more comprehensive view of what's happening, I tried to use an Observable in the Consumer and Producer classes and an Observer in a LogSynchrony class I created and an AsyncTask on the Logger screen to be monitoring the LogSynchrony class, but did not succeed. Could someone tell me a template or a north where should I go to solve my problem?