To avoid any impact to your project and to your Environment Variables, you can configure the Maven Compiler Plugin just to the project's POM, specifying the Source and Target java version
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.5.1</version>
<configuration>
<source>1.7</source>
<target>1.7</target>
</configuration>
</plugin>
...
</plugins>