IDEA project configuration error: Error: Module not specified, maven project has no maven operation

Error：Module not specified

The startup class that caused SpringBoot to fail to recognize the project.

wrong reason

This phenomenon is caused by the fact that the project cannot recognize Maven.

Solution

1. Re-import Maven
Maven -> Reload project

2. If there is no Maven here, enter the settings to set Maven.

Select the local Maven in the Maven home path column. (Try not to use the Maven that comes with the project, so that the project will report some inexplicable errors).
3. Clear the cache and restart

File -> Invalidate Caches, and wait for IDEA to restart.