[JDK 24] Provide JMODs as a separate download for deployment tool compatibility

[ingokegel]

Please provide a brief summary of the bug

The new JMOD-less builds introduced in Temurin 24 negatively impact deployment tools relying on jlink's cross-linking capabilities. This capability, as outlined by Alan Bateman in a highly voted Stack Overflow answer (+51 votes), demonstrates significant community interest:

https://stackoverflow.com/questions/47593409/create-java-runtime-image-on-one-platform-for-another-using-jlink

One prominent example is install4j which is a multi-platform installer builder. install4j allows users to select Adoptium as a JDK provider, generating customized runtime images containing only the necessary modules for the deployed application.

The install4j compiler itself is cross-platform, capable of creating installers for Windows, Linux, and macOS from any host platform. This critical functionality depends on jlink’s cross-linking capabilities.

Other widely used deployment tools and environments also leverage this functionality, including:

moditect: Maven plugin used to create custom Java runtime images across different platforms.

Badass Runtime Plugin: Popular Gradle plugin that builds platform-specific runtime images and installers using jlink.

Notably, other JDK providers such as Zulu, Corretto, and Liberica continue to offer JMOD-enabled builds in their Java 24 releases. Without official JMOD-enabled builds from Adoptium, these critical deployment scenarios will break, significantly affecting users who rely on Adoptium.

Did you test with the latest update version?

• Yes

Please provide steps to reproduce where possible

1. Download a 24.0 Temurin JDK for the current platform, extract it to $CURRENT
2. Download a 24.0 Temurin JDK for another platform, extract it to $TARGET.

Expected Results

Executing $CURRENT/bin/jlink with the argument --module-path $TARGET/jmods will generate a runtime image for the target platform.

Actual Results

The jmods directory is no longer present in the Java 24 builds, so the command cannot work and cross-linking is broken.

What Java Version are you using?

jdk-24+36

What is your operating system and platform?

Any

How did you install Java?

No response

Did it work before?

Yes, it worked with 23.

Did you test with other Java versions?

Corretto, Zulu and Liberica JDKs still include JMODs in Java 24, so cross-linking continues to work with those providers.

Relevant log output

[jerboaa]

It sounds like for this use-case you don't need the full JDK, but just the JMODs (for the other platforms). Can you verify this is something that would be sufficient?

So the idea to solve this problem for a specific cross-link scenario would be:

1. Download the JDK for the current platform (say Linux x64). Let that be available in $CURRENT.
2. Download JMODs for the target platforms (say Windows x64 and MacOS aarch64). Let them be available in $TARGET_WIN and $TARGET_MAC.
3. Produce a JDK bundle for Mac using: $CURRENT/bin/jlink --module-path $TARGET_MAC --add-modules [...] --output mac_aarch64_jdk.
4. Do the same for Windows.

The idea would be that the default JDK download would not include jmods folder, but be available for more specific use-cases like you have. Thoughts?

[ingokegel]

Yes, that would be fine!

For cross-linking, you only need the JMODs for the target platform, not a full JDK.

[jerboaa]

Just an update here. There wasn't an Adoptium PMC meeting this week so we'll discuss this next week in terms of deciding to go forward with providing that additional download and possible api.adoptium.net change to support JMODs. It should be fairly non-controversial. As for timing if this gets approved it'll likely land in July 2025 the earliest.

[ingokegel]

Wow, thanks for the fast response, that sounds really promising!