Simple Spring Boot app that runs on Google AppEngine. No attempt has been made to use the Google APIs - just a minimal Spring app that works.
Depends on spring-boot-legacy (which you will need to build and install locally):
$ git clone https://github.com/scratches/spring-boot-legacy
$ (cd spring-boot-legacy; mvn install)
$ git clone https://github.com/scratches/spring-boot-sample-gae
$ cd spring-boot-sample-gae
$ mvn gae:deploy
Also runs as a deployed WAR in WTP or regular Tomcat container. The main() app (normal Spring Boot launcher) should also work.