From JMV/Java run Python code that is using packages like requests, using GraalVM with Python module (graalpython).

• No java dependencies, only Java code example and maven pom.xml example to handle Python setup.
• Specify Python direct requirements in req.txt
• Ready for production! Python code can be bundled into .jar or be external. Python packages can be bundled into .jar, but GraalVM cannot yet execute this way, so they must be external to .jar file.

This template is based on https://github.com/hpi-swa-lab/graalpython-java-example

Changelog

1.1 (2021-6-23)

• venv name is configurable in maven pom.xml property <venv.name>, default venv
• pip requirements filename is configurable in maven pom.xml property <pip.install.requirements.filename>, default req.txt, usual requirements.txt

Quick start

1. Download GraalVM and set your JAVA_HOME to point to it.
   Make sure you have installed Python support:

"${JAVA_HOME}"/bin/gu install python

2. Compile the example:

mvn package

3. Run the example, using maven:

mvn exec:exec

or java, like:

java -jar target/java-python-graalvm.jar

See output like

Hello Java!
11.0.11
11.0.11+8-jvmci-21.1-b05
venv/bin/graalpython
Hello Python!  <-- from this point it is from python
3.8.5 (Fri Jun 25 17:55:09 CST 2021)
[Graal, GraalVM CE, Java 11.0.11]
{'data': {'indexingStatusForCurrentVersion': None}}  <-- json from python requests

To use

git clone https://github.com/paulvi/graalpython-java-template
mvn generate-resources

Deploy to production

Build:

mvn package

Distribute:
copy target/your.jar, pom.xml, req.txt to some new location

mkdir dist
cp ./{target/*.jar,pom.xml,req.txt} dist/

Run:

cd dist
mvn generate-resources
java -jar java-python-graalvm.jar

To recreate

This project is created as Python project (using graalpython), then converted into Java project by adding maven pom.xml.

Create new graalpython project:

mkdir dirname && cd dirname
graalpython -m venv venv
source venv/bin/activate

To see list of supported packages:

graalpython -m ginstall install --help

Install requests

graalpython -m ginstall install requests

Document dependencies

pip freeze > req.txt

Run (using graalpython actually):

python health.py

At this point this is still Python project. You can open with PyCharn, however PyCharn does not support (yet) running .py files, even though venv\bin\python is commonly used. To have this project as Java add maven pom.xml, src/main/java Java sources. How you can open in IDEA, Eclipse as maven project.

Converting into Java maven project:

cp pomx.xml, src/

Notes

Using src/main/python instead of src/main/resources as of 2021, has no benefits, as there is no maven plugins for python sources.

Docs & links

• https://www.graalvm.org/python/
• https://www.graalvm.org/reference-manual/python/
• https://www.graalvm.org/reference-manual/python/Packages/
• pip Requirements Files https://pip.pypa.io/en/stable/user_guide/#requirements-files
• pipreqs https://pypi.org/project/pipreqs/ can generate requirements.txt based on imports in project