javajava-9jlinkjava-modulejdeps

Creating custom runtime image dedicated for specific modular application

Let's say I'm developing a modular application that consists of 2 modules: com.spacey.explorer that depends on com.spacey.rocket module. I have their modular JAR files in some bin directory.

And I want to prepare lightweight JRE to run it. So obviously, I use the jlink tool:

$ jlink --module-path /opt/jdk-9/jmods:../bin --add-modules com.spacey.explorer --output ~/custom-jre3

Now when I list modules in my JRE I get the following:

$ java --list-modules 
com.spacey.explorer
com.spacey.rocket
java.base@9

That is, my application modules are bundled into JRE. But if I wanted to build a JRE that has just JDK-originated modules that are sufficient to run my application and keep my application modules separate, I have to know what my JDK dependencies are (in the example this is just java.base) and specify them explicitly like:

$ jlink --module-path /opt/jdk-9/jmods --add-modules java.base --output ~/custom-jre3

Is there any way to make jlink do this for me ? Or any tool that would figure out those JDK-originated dependencies for me?

Solution

  • You can use the jdeps tool. The option that could help is:

    jdeps --list-deps <path>

    Lists the dependences and use of JDK internal APIs.

    where <path> can be a pathname to a .class file, a directory, a JAR file.

    Note: Use jdeps -help to list out all the option and their syntax. You can use

    For example, I gave a try to a jar file in my machines .m2 folder, which would be treated as an unnamed module like:

    jdeps --list-deps /.m2/repository/org/apache/commons/commons-lang3/3.6/commons-lang3-3.6.jar

    Output::

    java.base
java.desktop
unnamed module: /.m2/repository/org/apache/commons/commons-lang3/3.6/commons-lang3-3.6.jar

    You can also make use of the 

    jdeps --jdk-internals --class-path <path> <path>

    Finds class-level dependences on JDK internal APIs. By default, it analyzes all classes on --class-path and input files unless -include option is specified.

    Update November 1,2017

    There is future revision change to make use of the same with jlink as : 

    jlink --module-path jmods --add-modules $(jdeps --print-module-deps myapp.jar) --output image