title: Hereku java spring boot app - version
body: <p>In documentation I read java 8 is default, but I use 9.0.4 version and I dont know where to set system.properties in my app project to push app to hereku to recognize and build my app, still failed from hereku maven building</p>
  
  <p><strong>You can specify a Java version by adding a file called system.properties to your application.
  Set a property java.runtime.version in the file:
  java.runtime.version=9</strong></p>