Compiling Java 17 using Maven in an Azure DevOps Pipeline

Using ubuntu-latest machines in an Azure DevOps pipeline, there is currently no support for versions beyond 11. So using a Maven@3 task to compile using a newer version fails. The workaround is to use a container version of Maven.

jobs:
  # build uberjar
  - job: ${{ parameters.jobName }}
    pool:
      vmImage: ubuntu-latest
    container: maven:3.8.1-openjdk-17-slim
    variables:
      - name: JAVA_HOME_11_X64
        value: /usr/local/openjdk-17
    steps:
      - template: steps-prepare-maven.yml
      - task: Maven@3
        displayName: build ${{ parameters.moduleName }} uberJar 
        inputs:
          mavenPomFile: pom.xml
          mavenOptions: -Xmx3072m $(MavenOpts)
          javaHomeSelection: 'path'
          jdkDirectory: '/usr/local/openjdk-17'
          publishJUnitResults: true
          testResultsFiles: "**/surefire-reports/TEST-*.xml"
          effectivePomSkip: true
          goals: -P production -pl ${{ parameters.moduleName }} -am $(MavenOpts) -Dmaven.test.skip=${{ parameters.skipTests }} $(BuildGoal)

We are using openjdk-17 and explicitly using javaHomeSelection and jdkDirectory to set our JAVA_HOME to match where the container puts the JDK.

So why are we also defining the environment variable JAVA_HOME_11_X64, you ask? Well, I have reusable templates that are used outside the container setting. For example, the steps-prepare-maven.yml file is a template that creates a settings.xml file using the project secrets and updates the revision based on my build parameters - I also use it on Windows jobs. Such steps use the default version, Java 11. When running inside the container, the JAVA_HOME_11_X64 takes precedence and the Maven steps in the reusable templates work correctly.

This is extracted from a template file, replace the parameters with what you need.

Credit: sfragata's answer to a github issue got me started. Then I stumbled around until I could fix my included templates using the environment variable.