Add Docker support with image build, CI workflow, and README updates

Author: CoderYellow

.dockerignore

@@ -0,0 +1,43 @@
+# Mirrors .gitignore so build artifacts and IDE/VCS files are NOT copied into the image.
+# The image rebuilds target/ and re-populates the Maven repo itself, then keeps them.
+.git
+.gitignore
+
+# Build output
+**/target/
+target/
+build/
+out/
+
+# IDE
+.idea/
+.idea_modules/
+*.iws
+*.iml
+.classpath
+.project
+atlassian-ide-plugin.xml
+
+# Maven / release scratch files
+.mvn/timing.properties
+.mvn/wrapper/maven-wrapper.jar
+dependency-reduced-pom.xml
+pom.xml.next
+pom.xml.releaseBackup
+pom.xml.tag
+pom.xml.versionsBackup
+release.properties
+buildNumber.properties
+
+# CMake
+cmake-build-*/
+
+# Crashlytics / Fabric
+com_crashlytics_export_strings.xml
+crashlytics-build.properties
+crashlytics.properties
+fabric.properties
+
+# Docker scratch
+Dockerfile
+.dockerignore

.github/workflows/build.yml

@@ -0,0 +1,60 @@
+name: build
+
+# Builds the project inside the Docker image (downloading all Maven dependencies and
+# producing the module jars), then publishes the image to GitHub Container Registry.
+on:
+  push:
+    branches: [ main, master ]
+    tags: [ 'v*' ]
+  pull_request:
+  workflow_dispatch:
+
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: ${{ github.repository }}
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      # Push everywhere except on pull requests (PRs from forks can't access GHCR).
+      - name: Log in to GitHub Container Registry
+        if: github.event_name != 'pull_request'
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Docker metadata
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          # metadata-action lowercases the image name, so mixed-case owners are fine.
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+          tags: |
+            type=ref,event=branch
+            type=ref,event=tag
+            type=sha
+            type=raw,value=latest,enable={{is_default_branch}}
+
+      # The Dockerfile runs `mvn install` (install the deps and build in the image build),
+      # keeping the downloaded deps, built jars and source inside the published image.
+      - name: Build and push image
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          push: ${{ github.event_name != 'pull_request' }}
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max

Dockerfile

@@ -0,0 +1,35 @@
+# Builds the whole project and KEEPS everything in the final image:
+#   - every downloaded Maven dependency        -> /root/.m2/repository
+#   - every built module jar / build artifact  -> /workspace/spark-test/**/target
+#   - the project source code                  -> /workspace/spark-test
+#
+# The source is copied as-is except for the files excluded by .dockerignore
+# (which mirrors .gitignore), so generated/IDE/VCS files are not brought in.
+#
+# Tests are NOT run during the image build: the scenario needs a Docker daemon
+# (Testcontainers), which is not available inside an image build. Dependencies and
+# jars are still fully resolved and produced.
+FROM maven:3.9-eclipse-temurin-17
+
+# Optional proxy support for local builds behind an HTTP proxy (empty in CI).
+# Example: docker build --build-arg HTTPS_PROXY=http://host.docker.internal:10809 .
+ARG HTTP_PROXY=""
+ARG HTTPS_PROXY=""
+ARG NO_PROXY=""
+ENV HTTP_PROXY=${HTTP_PROXY} HTTPS_PROXY=${HTTPS_PROXY} NO_PROXY=${NO_PROXY} \
+    http_proxy=${HTTP_PROXY} https_proxy=${HTTPS_PROXY} no_proxy=${NO_PROXY}
+
+WORKDIR /workspace/spark-test
+
+# Copy the project source (ignored files are filtered out by .dockerignore).
+COPY . .
+
+# Archive the (gitignore-filtered) source into the image as a tarball, before building
+# so it holds pure source with no target/ build output.
+RUN tar --exclude='*/target' -czf /workspace/spark-test-src.tgz -C /workspace spark-test
+
+# Install all dependencies and build the module jars; keep the local repo + target dirs.
+# Do NOT use a cache mount here on purpose: the downloaded deps must persist in the image.
+RUN mvn -B -e install -DskipTests
+
+CMD ["bash"]

README.md

@@ -99,3 +99,29 @@ mvn -pl spark-cloudera test
 # or both
 mvn test
 ```
+
+## Docker image
+
+The [`Dockerfile`](Dockerfile) builds the whole project inside the image and **keeps everything**:
+all downloaded Maven dependencies (`/root/.m2/repository`), every built module jar
+(`**/target/*.jar`), the project source (`/workspace/spark-test`), and a source tarball
+(`/workspace/spark-test-src.tgz`, captured before the build so it is pure source with no
+`target/`). The source is copied except for the files excluded by [`.dockerignore`](.dockerignore),
+which mirrors `.gitignore` (so `target/`, `.idea/`, `.git`, etc. are not brought in). Tests are
+skipped during the image build because Testcontainers needs a Docker daemon that isn't available
+there.
+
+```bash
+docker build -t spark-test .
+
+# Behind an HTTP proxy (e.g. local dev), pass it through:
+docker build --build-arg HTTPS_PROXY=http://host.docker.internal:10809 -t spark-test .
+```
+
+## CI / GitHub Container Registry
+
+[`.github/workflows/build.yml`](.github/workflows/build.yml) builds that image (installing the deps
+and building the jars in the image build) and publishes it to **GitHub Container Registry**
+(`ghcr.io/<owner>/spark-test`) on pushes to the default branch and on `v*` tags. It needs no extra
+secrets — it authenticates with the built-in `GITHUB_TOKEN` (`packages: write`). Pull requests build
+the image but do not push.