I’ve got multiple versions of Java installed and want/need to use different versions for different applications I’m supporting.

Example Problem

I have multiple versions of Java installed and need to use different versions depending on the source code I’m editing.

App1J8 - Uses Java 8
App2J11 - Uses Java 11
App3J17 - Uses Java 17

Solution

There are different ways people have done this. One solution uses Linux

Manually

I often just manually install the Java JDK and manually switch to the version I want to use. I define a function in my .bashrc file and then call it when starting bash.

function setJAVA_HOME(){
    :
    # Run "update-alternatives --list java" to see what's installed
    # and "sudo update-alternatives --config java"  to update
    # 
    # Use whatever version of Java my system is pointing to
    export JAVA_HOME=$(readlink -f /usr/bin/java | sed "s:/bin/java::" )

    # Force java8 to be used
    # export JAVA_HOME=/etc/alternatives/java_sdk_1.8.0_openjdk
    # export JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64/
    # export JAVA_HOME=/usr/lib/jvm/java-11-openjdk-amd64
    # export JAVA_HOME=/usr/lib/jvm/java-14-openjdk-amd64
    export JAVA_HOME=$HOME/.jdks/jdk-17.0.13
    # export JAVA_HOME=$HOME/.jdks/jdk-23.0.1
     pjs_addPath $JAVA_HOME/bin
}

Using UNIX Alternatives

See https://www.redhat.com/en/blog/alternatives-command for a intro to this command.

Debian update-alternatives

Debian unix uses update-alternatives which is like the original

To switch between different versions that have been installed use

# List the choices of Java Compiler installed and registered with alternatives
update-alternatives --list javac

# Pick a different version
update-alternatives --config javac
There are 2 choices for the alternative javac (providing /usr/bin/javac).

  Selection    Path                                          Priority   Status
------------------------------------------------------------
* 0            /usr/lib/jvm/java-11-openjdk-amd64/bin/javac   1111      auto mode
  1            /usr/lib/jvm/java-11-openjdk-amd64/bin/javac   1111      manual mode
  2            /usr/lib/jvm/java-8-openjdk-amd64/bin/javac    1081      manual mode

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

Installing JDKs

From Apt

On Ubuntu 20 and 22, you can install Java using this command. The problem is you don’t know what version will be installed.

sudo apt install default-jdk

Manually Downloading

Depending on which version of Oracle Java you install, you might need to sign away your life (jk, but you can’t just download it).

I’ve downloaded

JDK8 - https://www.oracle.com/java/technologies/downloads/#java8?er=221886
JDK11 - https://www.oracle.com/java/technologies/javase/jdk11-archive-downloads.html
JDK17 - https://www.oracle.com/java/technologies/javase/jdk17-archive-downloads.html
JDK21 - https://www.oracle.com/java/technologies/javase/jdk21-archive-downloads.html
JDK23 - https://www.oracle.com/java/technologies/javase/jdk23-archive-downloads.html

I download the TAR.GZ formatted file and then untar to $HOME/.jdks or $HOME/.apps.

Then make symlinks (if necessary) to simpler names.

cd $HOME/.jdks
tar tzf $HOME/Downloads/jdk-21_linux-x64_bin.tar.gz | head
tar xzf $HOME/Downloads/jdk-21_linux-x64_bin.tar.gz
ln -s jdk-21.0.5 jdk-21

Ubuntu 22 Linux using apt

Also see https://www.digitalocean.com/community/tutorials/how-to-install-java-with-apt-on-ubuntu-22-04

sudo apt install -y openjdk-8-jdk
sudo apt install openjdk-11-jre-headless
sudo apt install openjdk-17-jre-headless

Following instructions from Google’ing

I found this when seraching

https://www.digitalocean.com/community/tutorials/how-to-install-java-with-apt-on-ubuntu-22-04
https://askubuntu.com/questions/48468/how-do-i-install-java

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