<profile>  
       <id>jdk9</id>  
       <activation>  
           <activeByDefault>true</activeByDefault>  
           <jdk>9</jdk>  
       </activation>  
       <properties>  
           <maven.compiler.source>9</maven.compiler.source>  
           <maven.compiler.target>9</maven.compiler.target>  
           <maven.compiler.compilerVersion>9</maven.compiler.compilerVersion>
       </properties> 
</profile>