setup-maven/src/installer.ts

// Load tempDirectory before it gets wiped by tool-cache
let tempDirectory = process.env['RUNNER_TEMPDIRECTORY'] || '';

import * as core from '@actions/core';
import * as tc from '@actions/tool-cache';
import * as path from 'path';

if (!tempDirectory) {
  let baseLocation: string;
  if (process.platform === 'win32') {
    baseLocation = process.env['USERPROFILE'] || 'C:\\';
  } else {
    if (process.platform === 'darwin') {
      baseLocation = '/Users';
    } else {
      baseLocation = '/home';
    }
  }
  tempDirectory = path.join(baseLocation, 'actions', 'temp');
}

export async function getMaven(version: string) {
  let toolPath: string;
  toolPath = tc.find('maven', version);

  if (!toolPath) {
    toolPath = await downloadMaven(version);
  }

  toolPath = path.join(toolPath, 'bin');
  core.addPath(toolPath);
}

async function downloadMaven(version: string): Promise<string> {
  const toolDirectoryName = `apache-maven-${version}`
  const downloadUrl =
    `https://archive.apache.org/dist/maven/maven-3/${version}/binaries/${toolDirectoryName}-bin.tar.gz`
  console.log(`downloading ${downloadUrl}`)

  try {
    const downloadPath = await tc.downloadTool(downloadUrl)
    const extractedPath = await tc.extractTar(downloadPath)
    let toolRoot = path.join(extractedPath, toolDirectoryName)
    return await tc.cacheDir(toolRoot, 'maven', version)
  } catch (err) {
    throw err
  }
}