Maurice’s Blog

Refer: https://www.digitalocean.com/community/tutorials/how-to-install-java-on-ubuntu-with-apt-get

Installing default JRE/JDK

This is the recommended and easiest option. This will install OpenJDK 6 on Ubuntu 12.04 and earlier and on 12.10+ it will install OpenJDK 7.

Installing Java with apt-get is easy. First, update the package index:

sudo apt-get update

Then, check if Java is not already installed:

java -version

If it returns "The program java can be found in the following packages", Java hasn't been installed yet, so execute the following command, but you may want to move to Oracle 7 or 8 instead:

sudo apt-get install default-jre

Oracle JDK 7

This is the latest stable version.

sudo apt-get install oracle-java7-installer

Oracle JDK 8

Get repositories to install Java 8

$ sudo apt-get install python-software-properties
(Deprecated in Ubuntu 18.04)

$ sudo apt-get install software-properties-common
$ sudo add-apt-repository ppa:webupd8team/java
$ sudo apt-get update

Now Install Java 8
$ sudo apt-get install oracle-java8-installer

Manage various Java 8 Versions
$ sudo update-alternatives --config java

Oracle JDK 12
$ sudo add-apt-repository ppa:linuxuprising/java
$ sudo apt update
$ sudo apt install oracle-java12-installer

Managing Java (optional)

When there are multiple Java installations on your Droplet, the Java version to use as default can be chosen. To do this, execute the following command:

sudo update-alternatives --config java

It will usually return something like this if you have 2 installations (if you have more, it will of course return more):

There are 2 choices for the alternative java (providing /usr/bin/java).

Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/lib/jvm/java-7-oracle/jre/bin/java 1062 auto mode
1 /usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java 1061 manual mode
2 /usr/lib/jvm/java-7-oracle/jre/bin/java 1062 manual mode

Press enter to keep the current choice[*], or type selection number:

Setting the "JAVA_HOME" environment variable

To set the JAVA_HOME environment variable, which is needed for some programs, first find out the path of your Java installation:

sudo update-alternatives --config java

It returns something like:

There are 2 choices for the alternative java (providing /usr/bin/java).

Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/lib/jvm/java-7-oracle/jre/bin/java 1062 auto mode
1 /usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java 1061 manual mode
2 /usr/lib/jvm/java-7-oracle/jre/bin/java 1062 manual mode

Press enter to keep the current choice[*], or type selection number:

The path of the installation is for each:

/usr/lib/jvm/java-7-oracle

/usr/lib/jvm/java-6-openjdk-amd64

/usr/lib/jvm/java-7-oracle

Copy the path from your preferred installation and then edit the file /etc/environment:

sudo nano /etc/environment

In this file, add the following line (replacing YOUR_PATH by the just copied path):

JAVA_HOME="YOUR_PATH"

That should be enough to set the environment variable. Now reload this file:

source /etc/environment

Test it by executing:

echo $JAVA_HOME