File encoding has not been set, using platform encoding GBK

执行mvn package命令时，报以下警告：

File encoding has not been set, using platform encoding GBK

或

编码GBK的不可映射字符

解决方法：

在pom.xml中加入以下内容：

<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>