问 题：“Failed to execute goal org.apache.maven.plugins:maven-clean-plugin:2.4.1:clean
(default-clean) on project”?
出现情况：maven在clean或者install一个项目时，会出现此异常
解决方法：
1.有可能这个项目正在跑着在，关闭掉就好
2.有可能某个配置文件打开着在，修改完没有保存关闭
用英语来讲就是：
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.
