跳到主要内容

JEP 282: jlink: The Java Linker

Summary​

Create a tool that can assemble and optimize a set of modules and their dependencies into a custom run-time image as defined in JEP 220.

Non Goals​

This JEP does not commit the resulting tool to generate anything other than a modular run-time image.

It is not a goal of this JEP to define a standard or supported API for plugins. Instead, the plugin API will be strictly experimental. A future JEP may re-visit this topic once experience has been obtained using the plugin API defined by this JEP.

Motivation​

JEP 261 defines link time as an optional phase between the phases of compile time (the javac command) and run-time (the java run-time launcher). Link time requires a linking tool that will assemble and optimize a set of modules and their transitive dependencies to create a run-time image or executable.

Link time is an opportunity to do whole-world optimizations that are otherwise difficult at compile time or costly at run-time. An example would be to optimize a computation when all its inputs become constant (i.e., not unknown). A follow-up optimization would be to remove code that is no longer reachable.

Description​

A basic invocation of the linker tool, jlink, is:

$ jlink --module-path <modulepath> --add-modules <modules> --limit-modules <modules> --output <path>

where:

  • --module-path is the path where observable modules will be discovered by the linker; these can be modular JAR files, JMOD files, or exploded modules

  • --add-modules names the modules to add to the run-time image; these modules can, via transitive dependencies, cause additional modules to be added

  • --limit-modules limits the universe of observable modules

  • --output is the directory that will contain the resulting run-time image

The --module-path, --add-modules, and --limit-modules options are described in further detail in JEP 261.

Other options that jlink will support include:

  • --help to print a usage/help message
  • --version to print version information

Alternatives​

The alternative to a linking tool is to use platform-specific JDK and JRE image-build scripts. This approach would make it difficult to create custom run-time images.

Testing​

Beyond the expected set of unit tests to exercise the tool I, the JDK build will regularly exercise jlink by creating the JDK and JRE run-time images.

Risks and Assumptions​

The set of requirements for the tool is not complete at this time. The tool's extensibility is expected to evolve.

Dependences​