README.md

A Github Action to Export Your Maven Project's Version for Use in Subsequent Steps

I saw a great tweet from Bruno Borges about using Github Actions to derive the version of Java to be installed by analyzing the pom.xml of the build itself. It seems like a good enough idea, so I put it into practive here. Most of the magic lives in a very tiny JavaScript file, index.js:

Usage:

const core = require("@actions/core");
const github = require("@actions/github");
const exec = require("@actions/exec");

function cmd(cmd, args, stdoutListener) {
  exec
    .exec(cmd, args, {
      listeners: {
        stdout: stdoutListener,
      },
    })
    .then((ec) => {
      console.debug("the exit code is " + ec);
    });
}

try {
  cmd(
    "mvn",
    [
      "help:evaluate",
      "-q",
      "-DforceStdout",
      "-Dexpression=maven.compiler.target",
    ],
    // ["help:evaluate", "-q", "-DforceStdout", "-Dexpression=java.version"],
    (outputBuffer) => {
      const output = outputBuffer.toString();
      console.log(output);
      const varsMap = new Map();
      varsMap.set("java_version", output + "");
      varsMap.set("java_major_version", parseInt("" + output) + "");
      varsMap.forEach(function (value, key) {
        console.log(key + "=" + value);
        core.setOutput(key, value);
        core.exportVariable(key.toUpperCase(), value);
      });
    }
  );
} catch (error) {
  core.setFailed(error.message);
}

Basically, you put this at the very beginning of your Github Actions flow, right after the checkout, and it'll analyse your Maven pom.xml to determine which version of Java you've configured by having Maven tell it the value of maven.compiler.version. The program then exports the version and the major version of Java as a step output and an environment variable that you could use in subsequent steps.

So, assuming the following usage:

      - uses: joshlong/java-version-export-github-action@v17
        id: jve

You can use the exported environment variable:

      - uses: actions/setup-java@v3
        with:
          java-version: ${{ env.JAVA_MAJOR_VERSION }}

or reference the step's output values, like this:

      - uses: actions/setup-java@v3
        with:
          java-version: ${{ steps.jve.outputs.java_major_version }}

Now Github Actions will download whatever version of Java you've specified in your Maven pom.xml.

I really should make this work for Gradle... (Pull requests welcome!)