Upgrading to Java 11 LTS

[rtyley]

Base assumption: Project is already on Java 8

Overview

• You may want to complete Upgrading to Scala 2.13 #2 first - although Scala 2.12 supports Java 11, old project dependencies may use bytecode-manipulation libraries that didn't yet support Java 11. Updating to Scala 2.13 will give you a better chance of having up-to-date dependencies that can handle Java 11.
• Java 11 is the first version of Java optimised for ARM CPU architecture, eg AWS Graviton instances, for better performance & cheaper CPU cost. Java 11 has been a DevX recommendation since 2022.
• Note that at this point, we would recommend Upgrading to Java 21 LTS #8, rather than Java 11 (tho' if you are on Play 2.8, you may need to upgrade to Java 11 first, as a stepping-stone).

Checklist

• build.sbt
  • If you're publishing a library and consumers of your library are using Java 11, ensure that scalacOptions includes "-release:11" (even if you build under Java 21!)
  • Watch out for debianPackageDependencies, which may be set to include "openjdk-8-jre-headless" - you'll need to update that to "java11-runtime-headless"
  • Remove obsolete javaOptions, often these relate to RAM or GC (example), eg:
    • RAM (notes)
      • -XX:MaxRAMFraction
      • -XX:InitialRAMFraction
    • Garbage Collection (notes)
      • -XX:+PrintGCDetails
      • -XX:+PrintGCDateStamps
      • -XX:+UseGCLogFileRotation
      • -XX:NumberOfGCLogFiles
      • -XX:GCLogFileSize
• riff-raff.yaml (if this is a deployable application)
  • Ensure the AMIgo Recipe: specifies a recipe that includes Java 11, eg editorial-tools-focal-java11-ARM-WITH-cdk-base
• .github/workflows/ci.yml
  • Consider using the new guardian/setup-scala action in favour of setup-java & setup-sbt, which moves the place you specify your Java version from java-version into the .tool-versions file to become a source-of-truth for the Java version used by the project (example)

Examples

• Upgrade to Java 11 media-atom-maker#1149
• https://github.com/guardian/presence-indicator/pull/200
• https://github.com/guardian/ophan/pull/4047
• Frontend PRs
• Update to Java 11 tagmanager#534
• Update to Java 11 grid#4329