Since v2.7.4, Jython has supported the Java Platform Module System (JPMS), and since v2.7.2 (experimentally at first) it has provided a "slim" JAR as an alternative to the "standalone" and "classic" JARs. This project provides a simple example using both these features.
The project creates an application that performs a simple claculation. Use this as a starting point for your own work.
The build uses Gradle, but it should be possible to build it without installing Gradle: the project will fetch its own local copy.
The "standalone" and "classic" JARs include Jython dependencies in "shaded" form. That is, the classes are added to the Jython JAR with modified names. This results in a large JAR, quite possibly duplicating classes already present in the client project. It also breaks certain classes that check their own integrity (particularly the BouncyCastle classes behind the implementation of SSL).
Modern build tools like Maven and Gradle are also dependency managers. That is, components declare the dependencies they have and the tool resolves the full set of dependencies in your project. It then obtains them from repositories on the Internet or elsewhere.
The slim JAR does not contain its dependencies. It only requests them from the build tool. This means there is less duplication and the depended-on classes run with their proper names and integrity.
Jython 2 is unlikely ever fully to embrace the Java module system for its own use. (Jython 3 should.) It can, however, play nicely within a modular project.
This tutorial on dev.java is very helpful if you are still getting to grips with the detail of modules.
Packages from the slim JAR appear in the automatic module org.python.jython2.
Most of the dependency JARs also present themselves as modules (explicit or automatic) and will be found and added to the "module graph" by the JVM during start-up.
Some modules are not added to the graph because
their packages are referenced dynamically.
The declared dependencies are added to the module path by the build,
but surprisingly this does not get them into the module graph,
so they are missing at run-time.
To make available the full set available at run-time we use the option
--add-modules ALL-MODULE-PATH on the Java command.
The project shows how to take care of this in the build script build.gradle.
By varying the JVM options there,
you can see module resolution take place (add the --show-module-resolution option),
or watch it fail (suppress the --add-modules option).
Clone this repository onto your own machine. Open a shell in the root of the project. I'm using Windows PowerShell here, but the Unix equivalent is easy to work out.
The application is in a sub-project called app.
You can build it from the root of the project with:
PS demo-jython-slim-gradle> .\gradlew --console=plain app:install
> Task :app:compileJava
> Task :app:processResources NO-SOURCE
> Task :app:classes
> Task :app:jar
> Task :app:startScripts
> Task :app:installDist
BUILD SUCCESSFUL in 11s
4 actionable tasks: 4 executed
(I force Gradle to use a plain console because I find the colours unreadable.)
The command has compiled the program, obtained the Jython slim JAR and all its dependencies, and created a launch script you can run with:
PS demo-jython-slim-gradle> .\app\build\install\app\bin\app
42
If you think the word app appears too many times in this command,
you can run the application directly with Gradle:
PS demo-jython-slim-gradle> .\gradlew --console=plain app:run
...
> Task :app:run
42
but the idea of the install directory is that you can take its contents
and "install" them elsewhere,
to run any time you need 42 printed on the console, very slowly.
You can also ask for the contents as a zip or tar file.
The install directory has two subdirectories.
bin as we've seen contains the launch script.
lib contains the application JAR, the Jython JAR,
and everything they depend on that the JDK doesn't supply.
The sub-project called cli has no code of its own.
It simply names the Jython command as its main class.
You can build and run it from the root of the project with:
PS demo-jython-slim-gradle> .\gradlew --console=plain cli:install
> Task :cli:compileJava NO-SOURCE
> Task :cli:processResources NO-SOURCE
> Task :cli:classes UP-TO-DATE
> Task :cli:jar
> Task :cli:startScripts
> Task :cli:installDist
BUILD SUCCESSFUL in 12s
3 actionable tasks: 3 executed
PS demo-jython-slim-gradle> .\cli\build\install\cli\bin\cli
Jython 2.7.4 (tags/v2.7.4:3f256f4a7, Aug 18 2024, 16:49:39)
[Java HotSpot(TM) 64-Bit Server VM (Oracle Corporation)] on java17.0.7
Type "help", "copyright", "credits" or "license" for more information.
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