Sharing POJOs between Java backend and an Android application

I am developing an Android application with my friend. I am currently responsible for the backend while she is working on the Android part. The backend is developed in Java using Lambda functions running in AWS Amazon Cloud‎. The frontend and the backend are totally decoupled (Lambda functions are exposed via REST APIs) except for the POJOs used on both sides. POJOs are serialized by the application into JSON when calling an API and deserialized again into POJOs (very same ones) by the backend when handling API requests.

We want to keep POJOs on both sides exactly the same for obvious reasons but we are wondering what the proper way to do it is. We see the following two options:

1) Simply copy code on both sides. This has the disadvantage of changing common code independently which, sooner or later, will lead to a misallignment.

2) Move POJOs out to a separate library and include it as a dependency on both sides. This seems like a more proper way to solve this issue but how do we ensure that both me and my friend know that a POJO has been changed? Let's say I remove one field from a POJO and create a new version of the shared library. I push changes to our repository and then... tell my friend that I made some changes so she should pull them, build the new version and include it in her project?

Is there a different (better) way to address this issue? Currently the backend is built with Maven but I can switch to Gradle if this would help automate things and make our code consistent (Android Studio forces Gradle builds).

I found similar questions of other people but they were either a bit different or remained unanswered:

Sharing POJOs between Android project and java backend project

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