Download your desired JAR in server.jar and set the variables PORT and RAM!
Example:
# Build the image
docker build --pull --rm -f "Dockerfile" -t containercraft:latest "."
# Run it!
docker run -e "RAM=1G" -e "PORT=25565" containercraft:latest "."If you need Java 8 for Minecraft 1.8, get NachoSpigot!
(or change the 16 in the Dockerfile to 8)