Back end

Ubuntu Linux OS Ubuntu Server Docs

Apache HTTP server configured as reverse proxy Apache HTTP Server Project

JRE 8 Java 8th Edition

Apache Tomcat Java application server Apache Tomcat API

Web service application, incorporating:

Data

Embedded Apache Derby database Apache Derby API Docs
Hibernate ORM Hibernate Javadocs
Custom entity classes
Spring Boot Data Spring Boot Docs
Custom data repository interfaces

Service controllers

Spring MVC Spring MVC Docs
Custom controller classes
Custom Service classes

View composition & serialization

Jackson JSON Jackson Project Docs
Custom view classes & interfaces

Authentication

Google Sign In (external service; see https://developers.google.com/identity)

Front end

Android OS Android API reference

Data model

SQLite SQLiteDatabase
Room ORM Room Persistance Library
Custom entity and other model classes
Custom type converters
Data access object (DAO) interfaces

Remote service interfaces

Retrofit Retrofit Javadocs
ReactiveX ReactiveX Android Javadocs,ReactiveX Java Javadocs
Gson Gson Javadocs
Custom serializer/deserializers

View Model components

Android Lifecycle framework (ViewModel & LiveData)
Custom view model classes

View

Custom RecyclerView.Adapter and RecyclerView.Holder classes
Custom layouts

Controller

Custom activity and fragment classes

Authentication

Google Sign In (external service; see https://developers.google.com/identity)
Custom sign in service class