<properties>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
</properties>
参考：https://www.cnblogs.com/tongxuping/p/7257623.html
其他：
http://maven.apache.org/plugins/maven-compiler-plugin/examples/set-compiler-source-and-target.html
http://blog.csdn.net/kai161/article/details/50379418
http://blog.csdn.net/qh_java/article/details/52299062