Agree with @J-Dizzle,
I am a beginner in web-development and had a hard time solving this today.
Had similar problems when I was creating a SpringBoot project in STS.
Tried most of the solutions mentioned but they didn't work.
Tried removing .metadata
folder and re-building my springboot project but still nothing worked.
NOTE : I had multiple workspace in STS and this error occurred after migrating a project from one workspace to another.
Solution : All you need to do is restart your eclipse/STS IDE and it will work just fine.