Managing multiple installations of Java on a Mac

The last few years we’ve seen an increase in various Java distributions. Now there is OpenJDK in multiple flavors (Oracle, AdoptOpenJDK, Amazon Corretto), Eclipse OpenJ9 and Azul Zing. With this increased interest in the Java ecosystem there is suddenly multiple Java distributions and versions to test your applications against. Running applications in containers is one approach, but for local development one should consider jEnv.

Installing different Java versions

First off you need to know what kind of Java distribution (vendor, JRE/JDK) you want. I personally like AdoptOpenJDK due to its community backing of known companies and ease of installation. Let’s install some JDKs!

Assuming Homebrew is installed:

# Will require you to input your account password for privileged installation
brew cask install AdoptOpenJDK/openjdk/adoptopenjdk{8,11,13}

Introducing jEnv

jEnv is probably the most well-known version manager for Java. It is similar to nvm, rbenv and similar project for other technologies. There is however one downside with jEnv that’s worth a mention: missing Windows support (but have Linux support).

Installing jEnv

brew install jenv

Then add the following to your shells configuration file. For bash that would typically be ~/.bash_profile/~/.bashrc or ~/.zshrc for zsh.

export PATH="$HOME/.jenv/bin:$PATH"
eval "$(jenv init -)"

Restart your terminal application or resource your configuration. You should now be able to run jenv doctor to verify your installation and see the message Jenv is correctly loaded (ignore other warnings).

An optional but recommended step is to enable a couple of plugins:

# ensure that JAVA_HOME is correct
jenv enable-plugin export
# make Maven aware of the Java version in use (and switch when your project does)
jenv enable-plugin maven

Adding Java installations

Now that jEnv is correctly installed, it’s time to make it aware of the JDK’s which we installed earlier.

for version in 8 11 13
do
   jenv add /Library/Java/JavaVirtualMachines/adoptopenjdk-$version.jdk/Contents/Home
done

# You should now see output like this (exact versions can vary)
#
# openjdk64-1.8.0.232 added
# 1.8.0.232 added
# 1.8 added
# openjdk64-11.0.5 added
# 11.0.5 added
# 11.0 added
# openjdk64-13.0.1 added
# 13.0.1 added
# 13.0 added

jEnv is now ready for use in daily development workflows. To assign a default system-wide version use jenv global 11.0. If a specific project needs a different version of Java just use jenv local 13.0 when standing in the directory of that project. jEnv will then create a .java-version file that describes which JDK to use. This file can safely be checked in so that your whole team runs the same version of Java (if using jEnv of course).

Conclusion

Using Homebrew on a Mac, it is easy to install multiple versions of Java and manage it with jEnv. This enables experimentation with different flavors of Java and can lead to teams avoiding Java version conflicts.