Dockerizing a Java Web Application: A Step-by-Step Guide

🚀 Dockerizing a Java Web Application: A Step-by-Step Guide

Are you looking to containerize your Java-based web application? In this post, we’ll walk through creating an efficient, production-ready Dockerfile for a Java web app (like Spring Boot) using a multi-stage build approach.

📌 Why Use Docker for Java Applications?

• Portability: Run your app anywhere without worrying about dependencies.
• Consistency: Eliminate “It works on my machine” issues.
• Scalability: Deploy easily on Kubernetes or cloud platforms.

🛠 Step-by-Step Guide to Writing an Optimized Dockerfile

🏗️ 1. Project Structure

Your Java web application should follow this structure:

my-java-app/
│── src/                    # Java source code
│── pom.xml                 # Maven build configuration
│── Dockerfile              # Docker build configuration

📝 2. Writing the Dockerfile

This Dockerfile uses a multi-stage build to keep the final image lightweight and efficient.

# ==========================
# 1️⃣ Build Stage - Compiling the Java Application
# ==========================
FROM maven:3.8.7-openjdk-17 AS builder

# Set working directory inside container
WORKDIR /app

# Copy only pom.xml first to cache dependencies
COPY pom.xml .
RUN mvn dependency:go-offline

# Copy the complete source code
COPY src ./src

# Build the application (skip tests for faster build)
RUN mvn clean package -DskipTests

# ==========================
# 2️⃣ Runtime Stage - Running the Java Application
# ==========================
FROM openjdk:17-jdk-slim

# Set working directory
WORKDIR /app

# Copy the built JAR from the builder stage
COPY --from=builder /app/target/*.jar app.jar

# Expose application port (default 8080 for Spring Boot)
EXPOSE 8080

# Start the application
CMD ["java", "-jar", "app.jar"]

🔍 3. Understanding the Dockerfile

✅ Multi-stage Build: Reduces final image size by separating build and runtime stages.

✅ Maven Caching Optimization: COPY pom.xml . ensures dependencies are cached.

✅ Lightweight Runtime Image: Uses openjdk:17-jdk-slim for efficiency.

✅ Exposes Port 8080: The app will be accessible on http://localhost:8080.

⚙️ 4. Building and Running the Docker Image

📌 Step 1: Build the Docker Image

Run this command in your project directory:

docker build -t my-java-app .

📌 Step 2: Run the Container

docker run -p 8080:8080 my-java-app

📌 Step 3: Verify the Running Container

docker ps

Now, open http://localhost:8080 in your browser to access your application. 🎉

🏆 Best Practices for Java Dockerization

🔹 Use Multi-Stage Builds – Keeps image size small.

🔹 Optimize Maven Caching – Speeds up build times.

🔹 Use a Slim Base Image – Reduces attack surface and resource usage.

🔹 Skip Tests in Build Stage – Faster builds in dev/test environments.

🎯 Final Thoughts

Dockerizing a Java web app is straightforward when you follow best practices. With a clean Dockerfile, your app becomes portable, scalable, and production-ready.

Do you use a different approach? Let me know in the comments! 💬

Happy coding! 🚀