问 题：“Failed to execute goal org.apache.maven.plugins:maven-clean-plugin:2.4.1:clean
(default-clean) on project”?
This usually happens in Windows environments when the target folder is "locked". E.g.
when you are running your web application (looks like you do) and want to perform a mvn clean.
The application server/servlet engine locks the files so that mvn clean cannot delete
the files because they are locked.
Try to run this command when the web application is not running.
Edit: This also may happen if you have the target folder open in explorer
or editing a text file from target folder, etc.