Be ready and prepare Raspberry Pi for Java 9

   Java 9 is coming soon with many new features. Aside of continued discussion about Project Jigsaw impact, it's time to get prepared.

This article helps you to prepare your RaspberryPi environment with multiple installed JDKs.

Whole process is quite straight forward: 

The first step is to download the last stable release of java jdk-9. 

In the article we use the most recent build: jdk-9+170

http://jdk.java.net/9/

You can download JDK directly into your RapsberryPi or your local machine and then by using $scp command upload it to your RaspberryPi machine

$scp ./jdk-9-ea+170_linux-arm32-vfp-hflt_bin.tar.gz pi@<raspberrypi_ip>/home/pi

The next step is to login into your RaspberryPi machine  

$ssh pi@<raspberry_ip>

To unzip the downloaded JDK file execute following command:

$ sudo tar zxvf jdk-9-ea+170_linux-arm32-vfp-hflt_bin.tar.gz -C /opt

The command extracts the jdk-9 into the /opt folder

Now link java and javac with newly available JDK

$ sudo update-alternatives --install /usr/bin/javac javac /opt/jdk-9/bin/javac 1

$ sudo update-alternatives --install /usr/bin/java java /opt/jdk-9/bin/java 1

by using following command we select the jdk-9 available for us under the number 1

$ sudo update-alternatives --config javac

$ sudo update-alternatives --config java

at the end we verify our current java version by:

$ java -version

java version "9-ea"

Java(TM) SE Runtime Environment (build 9-ea+170)

Java HotSpot(TM) Client VM (build 9-ea+170, mixed mode)

$ javac -version

javac 9-ea

Congratulation your RaspberryPi is now running on Java 9 and you can switch between JDKs.