IDEA does not recognize the module (there is no blue square in the lower right corner of the module)

Summary of the recent encounter that Idea cannot recognize the module

I checked some methods, and some methods are not valid for my situation, so I will make a summary here.

The problem I encountered was that the files could not be displayed under the project, as shown in the picture below

Some bloggers say that simply deleting the .idea folder solves the problem.But after I delete it, the project cannot be recognized.

At this time, I created a new testtest module, which can be recognized by the idea. I opened the modules.xml file under .idea and found that the newly created module appeared under .At this time, we can make a bold guess, if we declare the .iml files under other modules here or not, it will be successful.

After adding it, it turned out to be a success.If it does not succeed automatically, click Rebuild Module.

Here I still can't run successfully after identification, Idea reported an error, as follows:

Here we do not configure the output path of the class file, we can set the output path according to the following figure.

Everyone's situation may be different, and it may not solve your problem. It is a reference for those who have the same problem as me.