Set up multiple JDKs with jenv and AdoptOpenJDK

2019-01-06

java jenv openjdk osx homebrew 

Happy new near everyone!

This short article describes how to set up multiple JDKs on a Mac for quick switching. The motivation behind this was that after the upgrade from JDK 10 to JDK 11 the @MockBeans annotation (originating from spring-boot-test) was not working anymore as methods from sun.misc.Unsafe had been deprecated. Due to an unwary brew update I suddenly had a new JDK on my system which broke the build of one of my projects.

I should note that this assumes you are using Homebrew as package manager to ease installation of binaries. This not only works for command line tools but also for OS X application, so you should really check it out.

Step 1: Install OpenJDKs from AdoptOpenJDK with brew

OpenJDK releases are available in a tap, meaning a separate repository of brew casks. brew tap adds the required repository so that you can use the casks in them.

$ brew tap AdoptOpenJDK/openjdk

We can see the available casks like so

$ brew search /adoptopenjdk/
==> Casks
adoptopenjdk                         adoptopenjdk11                     adoptopenjdk11-openj9                adoptopenjdk9
adoptopenjdk10                       adoptopenjdk11-jre                 adoptopenjdk8

Now we can install the OpenJDK versions we want to use:

$ brew cask install adoptopenjdk11
$ brew cask install adoptopenjdk10
$ brew cask install adoptopenjdk8

Step 2: Install and configure jenv

Before we start: what is jenv?

jenv is a version manager for java installations for the command line. Note that it does not install the JDKs, it just manages the currently active java version and what’s more important, per working directory.

$ brew install jenv

I’m using zsh as shell for the command line. If you’re interested, have a look at oh-my-zsh also, this greatly improves the zsh experience with loads of plugins for all kinds of tools. To enable jenv on zsh I execute

$ echo 'export PATH="$HOME/.jenv/bin:$PATH"' >> ~/.zshrc
$ echo 'eval "$(jenv init -)"' >> ~/.zshrc

Don’t forget to either source your *rc or to restart the shell so that the changes get effective.

Step 3: register JDKs with jenv

brew installs the JDKs into the folder /Library/Java/JavaVirtualMachines/, we now need to register each of them with jenv:

$ jenv add /Library/Java/JavaVirtualMachines/adoptopenjdk-11.0.2.jdk/Contents/Home/
$ jenv add /Library/Java/JavaVirtualMachines/adoptopenjdk-10.jdk/Contents/Home/
$ jenv add /Library/Java/JavaVirtualMachines/adoptopenjdk-8.jdk/Contents/Home/

NOTE: the pathes may differ on your machine, so please make sure they exist!

You can check whether the JDKs have been added correctly if you use the jenv versions command

$ jenv versions
* system (set by /Users/dhiller/.jenv/version)
  1.8
  1.8.0.202
  10.0
  10.0.2
  11.0
  11.0.2
  openjdk64-1.8.0.202
  openjdk64-10.0.2
  openjdk64-11.0.2

Step 4: Use jenv to specify the current JDK to use

Now that jenv knows the versions you can either set the JDK globally

$ jenv global 10.0
$ java -version
openjdk version "10.0.2" 2018-07-17
OpenJDK Runtime Environment AdoptOpenJDK (build 10.0.2+13)
OpenJDK 64-Bit Server VM AdoptOpenJDK (build 10.0.2+13, mixed mode)

or for a specific project in the project directory:

$ cd ~/projects/my_project
$ jenv local 1.8
$ java -version
openjdk version "1.8.0_202"
OpenJDK Runtime Environment (AdoptOpenJDK)(build 1.8.0_202-b08)
OpenJDK 64-Bit Server VM (AdoptOpenJDK)(build 25.202-b08, mixed mode)

To unset the version

$ jenv global system

or

$ cd ~/projects/my_project
$ jenv local --unset

Step 5: [Optional] Remove previous default Oracle JDK install

$ brew uninstall java

NOTE: I included this step because I had some interference on the command line, where jenv would not be able to override the chosen JDK, meaning that java -version still yielded the Oracle JDK. After I uninstalled the default Oracle JDK this went away. If you are using ~.zshrc or ~/.bashrc do not forget to remove manually setting JAVA_HOME and the like also as jenv will do that for you.

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