github actions: upgrade the plugins

.github/workflows/maven.yml

@@ -20,7 +20,7 @@ jobs:
         java-version: ${{ matrix.java }}
         distribution: 'temurin'
     - name: Cache Maven packages
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       with:
         path: |
           ~/.m2/repository

Dockerfile

@@ -0,0 +1,26 @@
+# Allows you to run this app easily as a docker container.
+# See README.md for more details.
+#
+# 1. Build the image with: docker build --no-cache -t test/vaadin8-sampler:latest .
+# 2. Run the image with: docker run --rm -ti -p8080:8080 -m256m test/vaadin8-sampler
+#
+# Uses Docker Multi-stage builds: https://docs.docker.com/build/building/multi-stage/
+
+# The "Build" stage. Copies the entire project into the container, into the /app/ folder, and builds it.
+FROM eclipse-temurin:11 AS BUILD
+RUN apt update && apt install unzip -y
+COPY . /app/
+WORKDIR /app/
+RUN ./mvnw -C clean test package -Pproduction
+WORKDIR /app/target/
+RUN ls -la
+RUN unzip *.zip -d app/
+# At this point, we have the app (executable bash scrip plus a bunch of jars) in the
+# /app/target/app/ folder.
+
+# The "Run" stage. Start with a clean image, and copy over just the app itself, omitting gradle, npm and any intermediate build files.
+FROM eclipse-temurin:11
+COPY --from=BUILD /app/target/app /app/
+WORKDIR /app/
+EXPOSE 8080
+ENTRYPOINT ./bin/app