Custom JDK Versions Per Project With SDKMAN!

SDKMAN! allows us to easily install and use different JDKs. It can become frustrating to have to change JDK versions manually for different projects. Fortunately, SDKMAN! has a solution to this in the form of the sdk env command. This command allows us to define a different JDK per project which can be easily switched to, without having to remember the JDK version. Additionally, it can be configured to automatically change to the required JDK when changing directories.

For more information about installing and using SDKMAN!, check out our article - Managing JDK Versions With SDKMAN!

Updating SDKMAN!

Before we can start using the sdk env command, we must first ensure we are using the latest version of SDKMAN! The software can be updated by using the sdk selfupdate command

% sdk selfupdate
No update available at this time.

Specifying a JDK Version For A Project

SDKMAN! uses a hidden file called .sdkmanrc which contains a parameter specifying which JDK version to use for a project. To configure and use this file is a simple 3 step process.

  1. Create the .sdkmanrc file. This can easily be created by navigating to the required directory and executing sdk env init
% sdk env init
.sdkmanrc created.
  1. Configure the version. Once we've created the file, edit it and add a line java=x.x.x.x specifying the version of Java to use. For example to use Adopt Open JDK version 11, the file would look like:
% cat .sdkman
  1. Initialize the environment. After editing the .sdkmanrc fille, we can configure the environment by executing the sdk env command.
% sdk env

Using java version 11.0.2-open in this shell.
% java -version
openjdk version "11.0.2" 2019-01-15
OpenJDK Runtime Environment 18.9 (build 11.0.2+9)
OpenJDK 64-Bit Server VM 18.9 (build 11.0.2+9, mixed mode

Specifying a JDK Automatically

Finally, we can get SDKMAN! to automatically change JDK to the version defined within .sdkmanrc by changing configuration. To do this, edit the ~/.sdkman/etc/config file and add/edit the property sdkman_auto_env=true. This will probably already exist and be set to false, so make sure you edit this setting if it is there rather than duplicating it.

Now, whenever you change into a directory containing a .sdkmanrc file in it, the JDK will automatically be changed to your desired version. Fantastic !

% cd project1 

Using java version 11.0.2-open in this shell.
% cd project2

Using java version 14.0.1-open in this shell.

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