Introduction
As a lot of programs require to have Java installed, this
article will guide you through the process of installing and managing different
versions of Java.
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:
sudo apt-get install default-jre
This will install the Java Runtime
Environment (JRE). If you instead need the Java Development Kit (JDK), which is
usually needed to compile Java applications (for example Apache Ant, Apache
Maven, Eclipse and IntelliJ IDEA execute the following command:
sudo apt-get install default-jdk
That is everything that is needed to
install Java.
All other steps are optional and must
only be executed when needed.
Installing OpenJDK 7 (optional)
To install OpenJDK 7, execute the
following command:
sudo apt-get install openjdk-7-jre
This will install the Java Runtime
Environment (JRE). If you instead need the Java Development Kit (JDK), execute
the following command:
sudo apt-get install openjdk-7-jdk
Installing Oracle JDK (optional)
The Oracle JDK is the official JDK;
however, it is no longer provided by Oracle as a default installation for
Ubuntu.
You can still install it using
apt-get. To install any version, first execute the following commands:
sudo apt-get install
python-software-properties
sudo add-apt-repository
ppa:webupd8team/java
sudo apt-get update
Then, depending on the version you
want to install, execute one of the following commands:
Oracle JDK 6
This is an old version but still in
use.
sudo apt-get install
oracle-java6-installer
Oracle JDK 7
This is the latest stable version.
sudo apt-get install
oracle-java7-installer
Oracle JDK 8
This is a developer preview, the
general release is scheduled for March 2014. This external article about Java 8
may help you to understand what it's all about.
sudo apt-get install
oracle-java8-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:
You can now choose the number to use
as default. This can also be done for the Java compiler (javac):
sudo update-alternatives --config
javac
It is the same selection screen as the
previous command and should be used in the same way. This command can be executed
for all other commands which have different installations. In Java, this
includes but is not limited to: keytool, javadoc and jarsigner.
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"
JAVA_HOME=”
/usr/lib/jvm/java-7-openjdk-amd64”
That should be enough to set the
environment variable. Now reload this file:
source /etc/environment
Test it by executing:
echo $JAVA_HOME
If it returns the just set path, the
environment variable has been set successfully.
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