add docker support

.github/workflows/build.yml

@@ -1,28 +1,48 @@
 name: Java CI
 
-on: [push]
+on: [ push ]
 
 jobs:
   build:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        java: ["8", "11", "17"]
+        java: [ "8", "11", "17" ]
 
     steps:
       - uses: actions/checkout@v3
         with:
           fetch-depth: 0
+
       - name: Set up Java
         uses: actions/setup-java@v3
         with:
           java-version: ${{ matrix.java }}
           distribution: "temurin"
           cache: "maven"
+
       - name: Build with Maven
         run: mvn --batch-mode --update-snapshots verify
+
       - uses: actions/upload-artifact@v3
         if: ${{ matrix.java == '8' }}
         with:
           name: commafeed.jar
           path: commafeed-server/target/commafeed.jar
+
+      # Docker
+      - name: Login to Container Registry
+        if: ${{ github.ref_type == 'tag' && matrix.java == '8' }}
+        uses: docker/login-action@v2
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Docker build and push
+        uses: docker/build-push-action@v4
+        with:
+          context: .
+          push: ${{ github.ref_type == 'tag' && matrix.java == '8' }}
+          tags: |
+            athou/commafeed:latest
+            athou/commafeed:${{ github.ref_name }}