Automatically provision specific versions of JDKs for Gradle tasks that require JDKs (JavaCompile, Test, JavaExec etc) . Choose from a variety of different JDK vendors which can be automatically installed on multiple OSs.

Gradle has a built-in concept of auto-provisioning Java Toolchains, which will automatically install JDKs if they do not exist on system running Gradle, however it's lacking in some aspects:

1. Gradle always uses AdoptOpenJDK/Adoptium.
   1. You may prefer a different JDK vendor. We use Azul Zulu for their MTS support. It is important to us to develop and test with the same JDK we use in prod.
   2. Adoptium does not provide macos aarch64 for Java 11, which we need for Apple Silicon Macbooks.
2. Once Gradle finds an appropriate JDK on disk for that Java language version, it is always used and never updated.
   1. As a company with tens of millions of lines of Java, we often bump into JVM bugs. It's highly desirable we test and deploy using the exact same version of JDKs.
   2. Similarly, it's important to us that the exact same JDK versions are used on local machines as well as CI.
3. Gradle does not handle JDK CA certificates.
   1. Many companies use TLS interception when network calls are made outside their corporate network. Gradle provides no way to install the relevant CA certificates into auto-provisioned JDKs. This means they cannot be used in such an environment, or require manual patching.
4. You cannot easily set up a mirror for auto-provisioned JDK downloads.
   1. There's a Gradle property you can set to change to server base uri, but this still leaves you writing and maintaining a service that replicates the adoptium api.
   2. An internal corporate mirror can be 100x faster than a public one, especially for CI builds.

gradle-jdks solves all of these problems:

1. You can choose your favoured JDK vendor.
2. Use the same JDK version for representative, reproducible builds on dev machines and in CI.
3. Automatically add JDK CA certificates.
4. Point to an internal mirror for JDKs.

Palantirians: you probably shouldn't use this plugin directly - either use gradle-jdks-latest for OSS or gradle-jdks-internal for internal projects which will set everything up for you.

First, you must apply the plugin. In the root project, Either use the new plugin syntax:

plugins {
   id 'com.palantir.jdks' version '<latest version>'
}

or the old buildscript method:

buildscript {
   repositories {
      mavenCentral()
   }
   
   dependencies {
      classpath 'com.palantir.gradle.jdks:gradle-jdks:<latest-version>'
   }
}

apply plugin: 'com.palantir.jdks'

Next up comes configuring the JDKs plugin:

jdks {
   // Required: For each Java major version you use, you need to specify
   //           a distribution and version.
   jdk(11) {
      distribution = 'azul-zulu'
      jdkVersion = '11.54.25-11.0.14.1'
   }
   
   jdk(17) {
      distribution = 'amazon-corretto'
      jdkVersion = '17.0.3.6.1'
   }
   
   // Optional: For each distribution, you can set a base url for a
   //           mirror to use instead of the default public mirror.
   // Default:  Whatever mirror is publicly provided by the vendor
   jdkDistribution('azul-zulu') {
      baseUrl = 'https://internal-corporate-mirror/azul-zulu-cdn-mirror'
   }
   
   // Optional: You can specify CA certs which will be installed into
   //           the extracted JDK to work with TLS interception.
   // Default:  No CA certs are added.
   caCerts.put 'corporate-tls-cert', '''
      -----BEGIN CERTIFICATE-----
      // snip
      -----END CERTIFICATE-----
   '''.stripIndent(true)
   
   // Optional: Where to store the JDKs on disk. You almost certainly
   //           do not need to change this. 
   // Default:  $HOME/.gradle/gradle-jdks
   jdkStorageLocation = System.getProperty("user.home") + '/custom/location'
}

Behind the scenes, gradle-jdks applies com.palantir.baseline-java-versions (another gradle plugin - more docs in link) to handle configuring the Java language versions. You will need to configure this plugin as well to tell it what Java language versions:

// Read the docs at https://github.com/palantir/gradle-baseline#compalantirbaseline-java-versions
javaVersions {
   libraryTarget = 11
   distributionTarget = 17
}

Supported JDK distribution can be found here.

New JDK distributions are easily added - you just need to:

1. Add an entry to JdkDistributionName
2. Add a JdkDistribution - Azul Zulu example.
3. Add the JDK distribution here.
4. Write some tests to check the path is being built correctly - Azul Zulu example.
5. Make a PR.

1. Run the Gradle wrapper/daemon with a certain JDK
   • This plugin will only run common tasks that require JDKs, like JavaCompile, Test, JavaExec, GroovyCompile etc (the aforementioned com.palantir.baseline-java-versions does this).
   • The daemon itself still requires a preinstalled JDK.
   • In future, we hope to implement this feature, although it is not currently scheduled to be worked on.

If you run you gradle invocation with --info --rerun-tasks, the JDK will be visible in the output:

$ ./gradlew compileJava --info --rerun-tasks
> Task :my-project:compileJava
Compiling with toolchain '/Users/username/.gradle/gradle-jdks/azul-zulu-17.34.19-17.0.3-a3ceab47882436a6'.

• gradle-jdks-latest applies this plugin and configures the latest JDK releases - primarily exists for Palantir use, enforcing consistency across our open-source projects.