Change effective on 18 October 2017
Heroku’s support for Java, Scala, Clojure, Gradle, and JRuby now includes the option of using JDK 8u151, 8u152, or 9.0.1. To set the JDK version for an application, create a system.properties file in the root directory of your project and put the following code in it:
For a complete list of supported versions, see the Dev Center documentation for Java. For more information on OpenJDK 8u151 and 8u152, see the OpenJDK documentation for Java 8. For more information on JDK 9.0.1, see the OpenJDK documentation for Java 9.