ERROR Source option 1.5 is no longer supported. Use 1.6 or later

Question

It all happens when I was trying to build a springboot application by ./mvnw clean install

When I first run the install command, it runs into followin

Answer 1

In IntelliJ:

1. Open Project Structure (⌘;) > Modules > YOUR MODULE -> Language level: set 9, in your case.
2. Repeat for each module.