Run tests on multiple java versions (#215)

Author: graebm

.github/workflows/ci.yml

@@ -51,3 +51,26 @@ jobs:
         python3 -c "from urllib.request import urlretrieve; urlretrieve('${{ env.BUILDER_HOST }}/${{ env.BUILDER_SOURCE }}/${{ env.BUILDER_VERSION }}/builder.pyz?run=${{ env.RUN }}', 'builder')"
         chmod a+x builder
         ./builder build -p ${{ env.PACKAGE_NAME }} --spec=downstream
+
+  java-compat:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        version:
+          - 8
+          - 11
+          - 17
+    steps:
+      - name: Checkout Sources
+        uses: actions/checkout@v2
+      - name: Setup Java
+        uses: actions/setup-java@v2
+        with:
+          distribution: temurin
+          java-version: ${{ matrix.version }}
+          cache: maven
+      - name: Build ${{ env.PACKAGE_NAME }} + consumers
+        run: |
+          java -version
+          mvn -B test