n00b here, just getting started with Docker.
This is (hopefully) an image that you add to any existing (Maven-built) runnable .jar project. Maven-built package should be found at target/app.jar (i.e., use
<build> <finalName>app.jar</finalName> </build>
in your pom.xml).
This image starts FROM vettl/amazon-linux:2014.03, RUNs rpm to install the Oracle JDK 8u20, then sets up the ONBUILD. All you should have to do is use this in the FROM line of your Dockerfile, which should appear right next to the pom.xml. The docker build then should ADD the file from target/app.jar, and run it as the ENTRYPOINT using /usr/bin/java -jar.