index.js

/**
 *
 * Uses <a href="http://twitter.com/brunoborges">Bruno Borges'</a> brilliant
 * <a href="https://twitter.com/brunoborges/status/1565783443216416768?s=21&t=EoHl3kqopkK5pry-VVsSZA">hack</a> to extract a property
 * from a Maven `pom.xml` and export it to an environment variable
 * or property that other things, like the `setup-java` Github Action, can use.
 *
 * @author Josh Long
 */
/* see: https://github.com/actions/toolkit */
const core = require("@actions/core");
const github = require("@actions/github");
const exec = require("@actions/exec");
const fs = require('fs');

/**
 * makes it a little more clean to exec something. make sure to redirect all other file descripters to stdout!
 * @param {*} cmd
 * @param {*} args
 * @param {*} stdoutListener
 */
function cmd(cmd, args, stdoutListener) {
    exec
        .exec(cmd, args, {
            listeners: {
                stdout: stdoutListener,
            },
        })
        .then((ec) => {
            console.debug("the exit code is " + ec);
        });
}

try {

    const maven = fs.existsSync('pom.xml')
    const gradleGroovy = fs.existsSync('build.gradle')
    const gradleKotlin = fs.existsSync('build.gradle.kts')

    console.log(maven)
    console.log(gradleGroovy)
    console.log(gradleKotlin)

    if (maven) { // maven build
        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);
                });
            }
        );
    }  //
    else {
        if (gradleGroovy || gradleKotlin) {
            cmd("./gradlew", [ ':properties','--property','sourceCompatibility' ], outputBuffer => {
                const buff = outputBuffer.toString();
                if (buff.indexOf ('sourceCompatibility')!=-1) {
                  console.log ('sourceCompatibility: ' + buff)
                }
                else {
                   console.log ('nope!')
                }
                
                
            });
        }
    }
} catch (error) {
    core.setFailed(error.message);
}