Project Template: Create a Docker image for a Java application

A template project to create a Docker image for a Java application. The example application exposes an HTTP endpoint.

Golang developer? Check out https://github.com/miguno/golang-docker-build-tutorial

Features:

• The Docker build uses a multi-stage build setup to minimize the size of the generated Docker image, which is 176MB
• Supports Docker BuildKit
• Java 17 (Eclipse Temurin)
• JUnit 5 for demonstrating how to integrate unit testing
• Maven for build management
• GitHub Actions workflows for Maven and Docker
• Optionally, uses just for running common commands conveniently, see justfile.
• Uses .env as central configuration to set variables used by justfile and other helper scripts in this project.

Requirements

Docker must be installed on your local machine. That's it. You do not need a Java JDK or Maven installed.

Usage and Demo

Step 1: Create the Docker image according to Dockerfile. This step uses Maven to build, test, and package the Java application according to pom.xml. The resulting image is 176MB in size, of which 170MB are the underlying eclipse-temurin image.

# ***Creating an image may take a few minutes!***
$ docker build --platform linux/x86_64/v8 -t miguno/java-docker-build-tutorial:latest .

# You can also build with the new BuildKit.
# https://docs.docker.com/build/
$ docker buildx build --platform linux/x86_64/v8 -t miguno/java-docker-build-tutorial:latest .

Optionally, you can check the size of the generated Docker image:

$ docker images miguno/java-docker-build-tutorial
REPOSITORY                          TAG       IMAGE ID       CREATED         SIZE
miguno/java-docker-build-tutorial   latest    1403a608d055   4 minutes ago   176MB

Step 2: Start a container for the Docker image.

$ docker run -p 8123:8123 miguno/java-docker-build-tutorial:latest

Step 3: Open another terminal and access the example API endpoint of the running container.

$ curl http://localhost:8123/status
{"status": "idle"}

Usage with just

If you have just installed, you can run the commands above more conveniently as per this project's justfile:

$ just
Available recipes:
    default             # print available targets
    docker-image-create # create a docker image (requires Docker)
    docker-image-run    # run the docker image (requires Docker)
    docker-image-size   # size of the docker image (requires Docker)
    evaluate            # evaluate and print all just variables
    send-request-to-app # send request to the app's HTTP endpoint (requires running container)
    system-info         # print system information such as OS and architecture

Example:

$ just docker-image-create

Notes

You can also build, test, package, and run the Java application locally (without Docker) if you have JDK 17+ and Maven installed.

# Build, test, package the application locally
$ mvn clean package

# Run the example application locally
$ java -jar target/app.jar