JEP 493: Linking Run-Time Images without JMODs

JEP 493: Linking Run-Time Images without JMODsopenjdk.org

📌 What Is This JEP About?

JEP 493 simplifies the use of the jlink tool by allowing developers to create custom Java runtime images without needing .jmod files.

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💡 Motivation

Before JEP 493, if you wanted to build a custom runtime image using jlink, you had to:

• Compile your code as a modular JAR

• Then generate a JMOD file using the jmod tool

• Only then could you run jlink to create a runtime image

This made the process more complicated and redundant—especially in build pipelines or for library authors.

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📦 What is a .jmod File?

A JMOD file is a format introduced with the Java Platform Module System in Java 9. It's:

• A package format for compiled module artifacts

• Contains .class files, native libs, configs, etc.

• Used internally by the JDK for standard modules

Think of it like a fatter version of a JAR—but mostly useful for JDK developers, not application developers.

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🛠️ Problem With JMODs

For most real-world modular applications:

• You already build modular JARs

• You rarely need native code or special packaging

• Creating .jmod files adds unnecessary steps

• Build systems like Maven and Gradle don't produce JMODs by default

This creates friction.

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✅ What JEP 493 Changes

JEP 493 allows jlink to:

• Accept modular JAR files directly

• Skip the need for .jmod files altogether

• Treat modular JARs and JMODs interchangeably as input to the module path

So now:

Modular JAR → jlink → Custom Runtime No intermediate .jmod step needed.

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🚀 Benefits of JEP 493

Benefit	Explanation
🧹 Simpler Workflows	No need to generate .jmod files manually
⚙️ Tooling Compatibility	Works smoothly with Maven/Gradle outputs (modular JARs)
📦 CI/CD Friendly	Easier automation in pipelines
🧩 Modular Adoption Boost	Lowers the barrier to adopting Java modules
🧪 No Loss of Functionality	Native libraries and launchers still supported in other ways

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📜 Summary

• .jmod files are no longer required to link custom runtimes

• jlink now accepts modular JARs directly

• This improves developer experience, simplifies builds, and removes redundancy

• JEP 493 is a quality-of-life improvement for modular Java projects