What is JLink?

The JDK gives you two tools that work together for packaging and distribution:

• jlink creates a trimmed runtime image.
• jpackage wraps that image into an installer or native package.

jlink works with modular applications. It starts from your application module, resolves its required modules, and then assembles a runtime image that includes only that module graph. That means you get the JDK modules you actually use, instead of shipping the whole JDK.

In practice, that image already contains a runnable java launcher and the platform modules your app depends on, so the target machine does not need a separate full JDK install.

One important detail: modules are included at the module level, not class-by-class. So if you depend on a large module just to use one class, you may still pull in more than you expected. jlink is great at trimming the JDK, but it cannot trim inside a module.

If your application is not modular, jlink is not the right tool. It needs named modules so it can resolve the dependency graph before building the image.

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jlink \
  --module-path $JAVA_HOME/jmods:mods \
  --add-modules com.myapp \
  --output myapp-runtime

This command tells jlink where to find the platform modules ($JAVA_HOME/jmods) and your application modules (mods), which root module to include, and where to write the custom runtime image.

From there, jlink walks the module graph:

• it starts at com.myapp;
• adds every transitive requires dependency;
• keeps only the JDK modules that are actually needed;
• writes the finished image to myapp-runtime.

If you add jpackage afterward, you can turn that image into a platform-specific installer instead of shipping a raw directory.

Use jlink when you want to distribute a modular application with a smaller, self-contained runtime. Then use jpackage if you want to turn that runtime into an installer for Windows, macOS, or Linux.

Think of the pipeline like this:

1. compile your module;
2. package it as a modular JAR;
3. link a custom runtime with jlink;
4. optionally wrap that runtime with jpackage.

So the short version is: jlink trims the runtime, jpackage ships it.