Java9 and Docker - minimalist future is here

Quick look at how to dish out those size zero docker images that packages your runtime app binaries

Steps to install java9 on ubuntu (included a provision script, invoked when vagrant launches)

sudo add-apt-repository ppa:webupd8team/java
sudo apt-get install oracle-java9-installer
sudo apt-get install oracle-java9-set-default
export JAVA_HOME=/usr/lib/jvm/java-9-oracle
export MODS=$JAVA_HOME/jmods/

confirm java version

> java -version
java version "9-ea"
Java(TM) SE Runtime Environment (build 9-ea+140)
Java HotSpot(TM) 64-Bit Server VM (build 9-ea+140, mixed mode)

now cd to your working directory

> cd /vagrant/
> tree
├── Dockerfile
├── Readme.md
├── src
│   └── com.greetings
│       ├── com
│       │   └── greetings
│       │       └── HelloWorld.java
│       └── module-info.java
└── Vagrantfile

compile HelloWorld java9 style

> javac -d mods/com.greetings src/com.greetings/module-info.java src/com.greetings/com/greetings/HelloWorld.java

run HelloWorld::main

> java --module-path mods -m com.greetings/com.greetings.HelloWorld
Hello World

create jar of HelloWorld

mkdir -p mlib
jar --create --file=mlib/com.greetings.jar --main-class=com.greetings.HelloWorld -C mods/com.greetings .

build your runtime image using the jlink command

> jlink --module-path mlib:$MODS --add-modules com.greetings --output image

> tree image -L 2
image
├── bin
│   ├── com.greetings
│   ├── java
│   └── keytool
├── conf
│   ├── net.properties
│   └── security
├── lib
│   ├── amd64
│   ├── jexec
│   ├── modules
│   ├── security
│   └── tzdb.dat
└── release

>./image/bin/com.greetings 
Hello World

build the Dockerfile

> docker build . -t greetings

run the built docker image

> docker run greetings
Hello World

size of docker images

> docker images 
greetings   latest    31f997624827  34 minutes ago      169.7 MB
<none>      <none>    fa96f037e908  36 minutes ago      169.7 MB
ubuntu      latest    e4415b714b62  5 days ago          128.1 MB