What to do if Maven does not download the necessary artifacts or dependencies?

If Maven does not download the necessary artifacts or dependencies, you can take the following steps:

1. Check internet and proxy settings, if they are used.

2. Clear the local Maven repository for the problematic artifact by deleting its folder in ~/.m2/repository.

3. Run the command with the -U flag to forcibly update dependencies:

   mvn clean install -U
   

4. Verify the correctness of the dependency coordinates (groupId, artifactId, version) in pom.xml.

5. Check the availability of repositories specified in pom.xml or Maven settings (settings.xml).

6. Review Maven logs to identify the cause of the error.

If the problem persists, you can try adding alternative repositories or check if the artifact has been removed from the central repository.