Add Java 21 GitHub Actions CI workflow

.github/workflows/java-21.yml

@@ -0,0 +1,71 @@
+# Java 21 CI with Maven
+name: Java 21 CI with Maven
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    types: [ labeled, opened, synchronize, reopened ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up JDK 21
+        uses: actions/setup-java@v4
+        with:
+          distribution: 'temurin'
+          java-version: 21
+          cache: maven
+
+      - name: Build with Maven
+        run: mvn -B verify -P run-its
+
+      - name: Generate JaCoCo badge
+        id: jacoco
+        uses: cicirello/[email protected]
+        with:
+          badges-directory: .github/badges
+          generate-branches-badge: true
+          generate-summary: true
+          summary-filename: coverage-summary_java-21.json
+          coverage-badge-filename: jacoco_java-21.svg
+          branches-badge-filename: branches_java-21.svg
+          coverage-endpoint-filename: jacoco_java-21.json
+          branches-endpoint-filename: branches_java-21.json
+
+      - name: Log coverage percentages to workflow output
+        run: |
+          echo "(java-21) coverage = ${{ steps.jacoco.outputs.coverage }}%"
+          echo "(java-21) branches = ${{ steps.jacoco.outputs.branches }}%"
+
+      - name: Upload JaCoCo coverage report
+        uses: actions/upload-artifact@v4
+        with:
+          name: jacoco-report-java-21
+          path: target/site/jacoco/
+
+      - name: Deploy to Coverage Branch
+        if: ${{ github.event_name != 'pull_request' }}
+        uses: crazy-max/ghaction-github-pages@v4
+        with:
+          target_branch: coverage
+          build_dir: .github/badges
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}  
+
+      - name: Comment on PR with coverage percentages
+        if: ${{ github.event_name == 'pull_request' }}
+        run: |
+          REPORT=$(<.github/badges/coverage-summary_java-21.json)
+          COVERAGE=$(jq -r '.coverage' <<< "$REPORT")%
+          BRANCHES=$(jq -r '.branches' <<< "$REPORT")%
+          NEWLINE=$'\n'
+          BODY="## JaCoCo Test Coverage Summary Statistics (java-21) ${NEWLINE}* __Coverage:__ ${COVERAGE}${NEWLINE}* __Branches:__ ${BRANCHES}"
+          gh pr comment ${{github.event.pull_request.number}} -b "${BODY}"
+        continue-on-error: true
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}