Supercharge Your Java Apps With Python Blogpost

Context.java

Context context = Context.newBuilder("python").
    allowAllAccess(true).
    option("python.ForceImportSite", "true").
    option("python.Executable", VENV_EXECUTABLE).
    build();

GraphRenderer.java

interface GraphRenderer {
  InputStream render(String function, int steps);
}

Main.java

Main.class.getClassLoader().getResource("venv/bin/python").getPath();

pom_1.xml

<id>enforce-graalvm-python</id>
<phase>validate</phase>
<goals><goal>enforce</goal></goals>
<configuration>
  <rules>
    <requireFilesExist>
      <message>JAVA_HOME must be a GraalVM with Python installed. Download GraalVM from https://www.graalvm.org/downloads and install the Python component: `gu install python`</message>
      <files><file>${env.JAVA_HOME}/bin/graalpy</file></files>
    </requireFilesExist>
  </rules>
  <fail>true</fail>
</configuration>

pom_2.xml

<executions>
  <execution>
    <id>Prepare venv</id>
    <phase>generate-resources</phase>
    <goals><goal>exec</goal></goals>
    <configuration>
      <executable>${env.JAVA_HOME}/bin/graalpy</executable>
      <arguments>
        <argument>-m</argument>
        <argument>venv</argument>
        <argument>venv</argument>
      </arguments>
    </configuration>
  </execution>
  <execution>
    <id>Install required packages into venv</id>
    <phase>generate-resources</phase>
    <goals><goal>exec</goal></goals>
    <configuration>
      <executable>venv/bin/pip</executable>
      <arguments>
        <argument>install</argument>
        <argument>pygal==2.4.0</argument>
      </arguments>
      <environmentVariables>
        <VIRTUAL_ENV>${project.basedir}/venv</VIRTUAL_ENV>
      </environmentVariables>
    </configuration>
  </execution>
</executions>

pom_3.xml

<resource>
  <directory>${project.basedir}</directory>
  <includes>
    <include>venv/**/*</include>
  </includes>
</resource>

PyGalRenderer.java

Value pygalRendererClass = context.getPolyglotBindings().getMember("PygalRenderer");
Value pygalRenderer = pygalRendererClass.newInstance();
pygalRenderer.as(GraphRenderer.class);

pygalrenderer.py

import polyglot
polyglot.export_value("PygalRenderer", PygalRenderer)

renderer_1.py

class PygalRenderer:
  def render(self, func, steps):

renderer_2.py

    values = []
    x = -100
    while x < 100:
      values.append(eval(func, globals={"x": x, **math.__dict__}))
      x += 200 / steps

renderer_3.py

    chart = pygal.Line(fill=False)
    chart.add(f"f(x) = {func}", values)
    svg_data = chart.render()

renderer_4.py

    stream = SVGInputStream()
    stream.this.bytestream = iter(svg_data)
    return stream

svg_input_stream.py

class SVGInputStream(java.io.InputStream):
  def read(self, *args):
    ...