Java 9 setup options

Installing Java 9

Option 1: Ops Tools
If you only need to use Java 9 with Maven, you can use our 'Ops Tools' project. This will run Maven with the desired Java version (defaults to 9, but you can switch to Java 7 or 8). Follow the instructions in the README of this project. This option has two benefits; No need install Java on you machine (it runs in a container). And you will always be using the latest version of Maven and Java update version (the bit after 'u' in '8u144' or 'minor'/'patch' version in Java 9). Beware that you will be using OpenJDK when using this option, and not Oracle JDK.

Option 2: Plain install
Go to the Oracle website (http://www.oracle.com/technetwork/java/javase/downloads/jdk9-downloads-3848520.html), download and run installer.

Option 3: Other

* Homebrew: https://stackoverflow.com/questions/24342886/how-to-install-java-8-on-mac
* Jenv: http://www.jenv.be/ 
* Java version manager: https://github.com/shyiko/jabba
* Extendable version manager: https://github.com/asdf-vm/asdf

Switching between versions:

When using the Ops tools you can switch versions by exporting a variable:

```
export OPS_TOOLS_MVN_JAVA_VERSION=8
```

When using Homebrew or the plain install you can do:

```
export JAVA_HOME=`/usr/libexec/java_home -v 1.8`
export JAVA_HOME=`/usr/libexec/java_home -v 9`
```

Please check the documentation for the other options.