404 appears on the page when troubleshooting springboot startup

When I was developing today, there was no problem with the Contronller code and the front-end html. I found that when the browser entered localhost:8080, 404, so I checked and found that the SpringbootWebApplication file was placed in the subdirectory.
The startup file of springboot must be placed in the parent directory to detect that

resources can be accessed normally after Contronller modification is completed.