You might want to take a look at the App Engine
docs which may answer some of your questions. You may find that App Engine may replace some parts of this stack and others may not work well or at all. For example, you'll likely need to use
Task Queues and
Cron Tasks instead of Spring Scheduler. Running Spring Boot on top of App Engine is largely redundant and there are
other issues which require workarounds. For Spring Data, App Engine provides its own EntityManagerFactory and
JPA implementation.
You have access to managed MySQL instances in the form of
Google Cloud SQL. Spring Framework and Spring Rest are known to work, and you will have no problems with any JavaScript frameworks like Bootstrap or AngularJS.