how to use appium to get the context of an already running app?

I have an android app A that invokes another android app B.

I want to write test that starts app A, click a button which opens app B.

I then want to click a button in app B. Which returns the focus to app A and sends it some data.

Is it possible to get the context of app B when it's open by app A?

Usually I open an app myself and get it context from that.

like this:

AndroidDriver AndroidDriver = new AndroidDriver( "http://localhost:53761/wd/hub" , capabilitiesObj);