Enforcing JDK version in Gradle

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Keep team using same version can be a challenge, but I bring an easy way to enforce that.

Last week a fried of mine faced a very special problem with a build in CI/CD pipeline.
In its Dockerfile, he wasn’t setting a specific JDK version.
This reponsibility was so, automatically, transfered to the image eclipse-temurin:21.
He was using version 21.0.9 then image updated to 21.0.10 and bang… build started to fail.

A some time I wanted to write about similar thing:

How could we keep same JDK version when working in a team?

Is very easy to us, while working in a team, have different versions, e.g.:

  1. In our local JAVA_HOME
  2. In our IDE
  3. In CI/CD
  4. And so on

And indepently which JDK version manager you’re using:

  1. manually (i was this guy a long time a go)
  2. sdkman (today is my favorite)
  3. jenv
  4. etc

It’s very simple:

  1. We create a file in root project that containing a version, e.g. .java-version: 
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     21.0.9
  2. In Gradle(build.gradle.kts - yes I prefer kotlin over groove), set the toolchain to use that major version: 
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     val projectJdkFullVersion = file(".java-version").readText().trim()
 val projectJdkMajorVersion = projectJdkFullVersion.substringBefore('.').toInt()

 java {
   toolchain {
     languageVersion.set(JavaLanguageVersion.of(projectJdkMajorVersion))
   }
 }
  3. We create a task that will check the version: 
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     val checkJavaVersion by tasks.registering(Task::class) {
   doLast {
     val jdkRuntimeVersion = System.getProperty("java.version")
     if (!jdkRuntimeVersion.startsWith(projectJdkFullVersion)) {
       throw GradleException("Requires JDK $projectJdkFullVersion, but found $jdkRuntimeVersion")
     }
   }
 }
  4. Bind the task validation compile task in Gradle Lifecycle: 
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     tasks.compileJava {
   dependsOn(checkJavaVersion)
 }

In case the environment isn’t using the expected version, it’ll fail:

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❯ gradlew build
> Task :checkJavaVersion FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':checkJavaVersion'.
> Requires JDK 21.0.9, but found 21.0.10

* Try:
> Run with --stacktrace option to get the stack trace.
> Run with --info or --debug option to get more log output.
> Run with --scan to get full insights.
> Get more help at https://help.gradle.org.

BUILD FAILED in 974ms
1 actionable task: 1 executed

That’s it.
Everywhere your project is on, it’ll always be running on same version and be consistent.

That care with your versions.
When updating, even in case its a “low importance”.
Like the example, it was just “21.0.9 to 21.10”, it can result in fail on your end.
Take a moment to read the release notes.
Remember: if you don’t assume the responsibility about your version, your code… someone will do it.

xoff.