After formal participation in the work, always use maven frequently, from SVN checkout project, to project into Maven project, every time will encounter that red small exclamation mark, make people irritable. This time I want to record it, I can easily solve the same problem, and share my experience. To be honest, this is really low for most people, but I'm just recording my growth.
1, first, we see the red exclamation mark of these items
2. Select Windows, click Preferences, click Maven, select Installations,
3, then select User Settings
This time the MAVEN library will automatically download the jar package you need for your project, and if there is a red exclamation mark after the update, it may be that the MAVEN library does not have some of the jar packages you need, so you can download it yourself and copy it manually to your local maven library.
4, finally, you can also choose to clean your project, click on Project's Clean option.
5. Some follow-up notes about Maven will be uploaded ...
The MAVEN project stuff.