Whilst taking a quick look into the Hilla Web Framework the documentation includes some useful steps for deploying a jar to heroku.

Deploying a jar straight to heroku is an alternative to the approach that builds and deploys from your git repo.

Those steps are summarised here:

heroku login

heroku plugins:install java

heroku create --no-remote --region=eu teggr-some-app-name

heroku config --app=teggr-some-app-name

heroku config:set --app=teggr-some-app-name COM_ROBINTEGG_SOME_VALUE=a value

mvn package -Pproduction

heroku deploy:jar target\some-app-name-1.0-SNAPSHOT.jar --app 

heroku logs --tail teggr-some-app-name

heroku addons:create heroku-postgresql -a teggr-some-app-name