1. Find problems
right click pom.xml, run as – > After Maven install, you will see some similar messages in the console, such as errors in Maven repository, repos, org, mortbay, jetty, servlet-api-2.5, 6.1h.14.1, servlet-api-2.5, 6.1h.14.1, jar and so on. Pom.xml displays a red cross

2. Cause analysis
the package was not downloaded correctly

3. Solution
find the directory of the package, delete the package and download it again. After downloading again, test it with Maven test, and the Red Cross disappears