How to add external libraries such as Retrofit and butterknife in Android Source code packages?

[Ragesh Antony]

I am building a custom rom from AOSP source code

I first decided to edit some AOSP apps from AOSP source tree by downloading and importing to Android Studio

I selected ExactCalculator for training

But the AOSP don't have Build.gradle to add my dependencies .

I added some material components and also Retrofit ,Gson, Butterknife and dagger 2 in Android Studio built.gradle and implemented currency converter via an API in AOSP stock Exact Calculator

Now I overwritten the packaage src folder in AOSP with my modified srcs

But now my doubt is , since packages in AOSP source code don't have build.gradle only Android.mk, how can I add this libraries for building the AOSP source?