This project contains an app built in getting started tutorial for Vaadin Flow, but with a JPA/Java EE backend.
Import it to the IDE of your choice as a Maven project.
Deploy with help of tutorial https://blog.payara.fish/payara-server-basics-adding-payara-server-to-intellij-idea
and open http://localhost:8080/tutorial-with-jpa-1.0.0-SNAPSHOT/ in browser.