Spring Boot's Maven plugin currently forks a separate process for the web application that cannot be debugged easily from most IDEs. Most information online suggests that one set up a remote debugging session.
Instead, it is easiest to right click on your main() method and choose "Debug YourClass....main()—You'll be hitting breakpoints in no time.
For more information see the following Spring Boot issues:
The month of July has sped past, but I've captured a few moments from the summer; Willow being lazy on the porch, scenes from various walks, and hot air balloons at night.