Github-actions: cache repo to speed up maven builds

For completeness, this is an example of how to cache the local Maven repository on subsequent builds:

steps:
  # Typical Java workflow steps
  - uses: actions/checkout@v1
  - name: Set up JDK 11
    uses: actions/setup-java@v1
    with:
      java-version: 11
  # Step that does that actual cache save and restore
  - uses: actions/cache@v1
    with:
      path: ~/.m2/repository
      key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}
      restore-keys: |
        ${{ runner.os }}-maven-
  # Step that runs the tests
  - name: Run tests
    run: mvn test

See this page for more details.

As of 2021, the most up to date official answer would be

- name: Cache local Maven repository
  uses: actions/cache@v2
  with:
    path: ~/.m2/repository
    key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}
    restore-keys: |
      ${{ runner.os }}-maven-

taken from an official github example at https://github.com/actions/cache/blob/master/examples.md#java---maven