[M2]How to change the m2's defalut webapp dir to my own webroot dir?

[Hong Xing]

Hi all,

In my previous projects, I have the following project layout:

my-webapp
|-- pom.xml
|-- WebRoot
|   |-- index.jsp
|   `-- WEB-INF
|       `-- classes
|       `-- lib
`-- src

When I used "mvn package" to package my war, it can't find my WebRoot and 
failed.
So how can I change the m2's defalut webapp dir to my own webroot dir in 
pom.xml?