Change effective on 03 February 2016
Heroku’s support for Java 7 has been upgraded to include OpenJDK 7u95. This is now the default JDK 7 for all Java, Scala, Clojure, Groovy and JRuby applications. This version will be installed after your next deploy if you are configured to use Java 7. To manually set the JDK version, create a
system.properties file in the root directory of your project and put the following code in it:
JDK 8 remains the default Java version on Heroku.