Installing (multiple) Java on MacOS managed by jEnv

Install some Java!

I'm gonna install three version's from openjdk using Homebrew! We should all know what Homebrew is by now...
$ brew install openjdk@17
$ brew install openjdk@21

Create some Symlinks

As far as I understand it MacOS has a special Java VM folder where it installs the JVMs. We'll create symlinks to versions we just installed from Homebrew.
sudo ln -sfn /opt/homebrew/opt/openjdk@17/libexec/openjdk.jdk /Library/Java/JavaVirtualMachines/openjdk-17.jdk
sudo ln -sfn /opt/homebrew/opt/openjdk@21/libexec/openjdk.jdk /Library/Java/JavaVirtualMachines/openjdk-21.jdk

Install jEnv

jenv is a Java installation version manager. Install with Homebrew as well:
$ brew install jenv

Add the following to your shell's .rc file so jenv is executed upon terminal startup

# Setup JEnv to install run
export PATH="$HOME/.jenv/bin:$PATH"
eval "$(jenv init -)"
# Have JAVA_HOME set by JEnv for us...
jenv enable-plugin export

Source the file to apply the changes
source ~/.zshrc # or ~/.bash_profile, ~/.bashrc, etc.

Add the JVMs to jenv

Add the versions in Java VM folder to jenv so it can manage them
jenv add /Library/Java/JavaVirtualMachines/openjdk-17.jdk/Contents/Home/
jenv add /Library/Java/JavaVirtualMachines/openjdk-21.jdk/Contents/Home/

See the versions installed by jenv

You can see the installed versions by echo ${JAVA_HOME}

$ jenv versions
* system (set by /Users/user/.jenv/version)
  17
  17.0
  17.0.12
  21
  21.0
  21.0.4
  openjdk64-17.0.12
  openjdk64-21.0.4

See which version of Java you're using:

$ java -version
openjdk version "17.0.12" 2024-07-16
OpenJDK Runtime Environment Homebrew (build 17.0.12+0)
OpenJDK 64-Bit Server VM Homebrew (build 17.0.12+0, mixed mode, sharing)

Set/unset global version of Java

$ jenv global 21.0.2
$ jenv global --unset

Set/unset local version of Java

This will add a .java-version file in the directory you're currently in so you can commit it as a part of your Java project.

$ jenv local 21.0.2
$ jenv local --unset

Congrats! You've just installed Java on your MacOS! Have fun on your Java/Kotlin projects! 🥳