Scenario:
I am planning to build a system that has 2 components. A Web App (Angular) that would push some data to Firebase. Before the data gets pushed , I want it to get validated by a server-side Java code. The data getting pushed to Firebase is fed to an Android application that consumes the data from Firebase. The Android user can perform some actions like changing the state of data. Before the data gets changed again there should be a server side code to validate it.
Question:
Where does the server-side code reside? Do we need a third party Web App hosting service other than Firebase?
If my code is in Java 7, what can be the possible options available?
If at all we use a third party server, how does the server communicate with a Firebase server?
Also can you please help me understand (if possible) how can we make sure that the data getting pushed to Firebase server gets validated by the server-side code before getting pushed?