Here I developed and wrote detailed steps of Spring_Boot Calculator Application and Its robust web-based calculator that provides both a RESTful API and an intuitive user interface for performing arithmetic operations. Built with modern Java technologies and following best practices, this application is a practical tool demonstrating Spring Boot application development.

Core Features

Basic arithmetic operations (Addition, Subtraction, Multiplication, Division)
RESTful API endpoints
Web-based user interface
Docker support
Error handling for invalid operations
Real-time calculation

Technologies Used

Java 11
Spring Boot 2.7.0
Maven
Docker
HTML/CSS/JavaScript
RESTful API

Prerequisites

Java JDK 11 or higher
Maven 3.6 or higher
Docker 

Getting Started Local Setup and Clone the repository

git clone https://github.com/yourusername/Spring-Boot-calculator-app.git
cd Spring-Boot-calculator-app

Build the project

mvn clean package

Run the application

java -jar target/calculator-0.0.1-SNAPSHOT.jar

The application will be available at http://localhost:8080

or if you get the error occurs during the mvn clean package, we need to create the Maven wrapper files first. Let's fix this by creating the necessary Maven files by following ways:

Create Maven Wrapper files:

# Navigate to your project directory
cd calculator

# Initialize Maven Wrapper
mvn -N io.takari:maven:wrapper

Make the Maven wrapper executable:

chmod +x mvnw

Our project structure:

calculator/
├── src/
│   └── main/
│       ├── java/
│       └── resources/
├── .mvn/
│   └── wrapper/
│       ├── maven-wrapper.jar
│       └── maven-wrapper.properties
├── mvnw
├── mvnw.cmd
├── pom.xml
└── Dockerfile

Build the Docker image:

docker build -t <Image-Name:tag> .

Run the container:

docker run -p 8080:8080 <Image-Name:tag>

After running the calculator application container, you can check it in several ways:

Through your web browser:

#Open your browser and visit:
http://localhost:8080

Using curl command in terminal:

# Test the basic endpoint
curl http://localhost:8080

# Test the calculator API
curl -X POST http://localhost:8080/api/calculator/calculate \
-H "Content-Type: application/json" \
-d '{"num1": 10, "num2": 5, "operation": "add"}'

Check if the application is running:

# Check running processes on port 8080
lsof -i :8080

# Check Java processes
ps aux | grep java

Process of pushing your calculator application's Docker image to Docker Hub

Login to Docker Hub from terminal:

# Login to Docker Hub
docker login
# Enter your Docker Hub username and password when prompted

Tag your Docker image:

# Format: docker tag local-image:tag username/repository:tag
docker tag calculator-app yourdockerhubusername/calculator-app:latest

Push the image to Docker Hub:

# Push the image
docker push yourdockerhubusername/calculator-app:latest

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Important Note that:

Sometimes, when we run the docker command in GKE cluster "sudo docker run -p 8080:8080 lishan2023/calculator-app:latest" then result got the error

WARNING: The requested image's platform (linux/arm64/v8) does not match the detected host platform (linux/amd64/v3) and no specific platform was requested

exec /usr/local/openjdk-11/bin/java: exec format error

means that, The error you're encountering indicates a platform mismatch between the Docker image you're trying to run and the architecture of your host system. The image lishan2023/calculator-app:latest appears to be built for linux/arm64, but your host system is running on linux/amd64 (a different CPU architecture). This is why you're seeing the error:

exec /usr/local/openjdk-11/bin/java: exec format error

This issue typically happens when trying to run an image built for a different CPU architecture than the one your system uses. Here's how you can resolve this: Check Your Host's Architecture

uname -m

If it outputs x86_64, you're using an amd64 (64-bit Intel/AMD) architecture.

If it outputs aarch64 or arm64, you're using an arm64 architecture. Since your error indicates that your system is running on linux/amd64, but the Docker image is built for linux/arm64, we need to resolve this architecture mismatch.

Use a Multi-Architecture Docker Image Many Docker images are multi-architecture, meaning they can run on both arm64 and amd64 systems. If the image you're using is multi-architecture, Docker will automatically choose the right one. However, if it isn't, you can try forcing Docker to use the correct platform.

Rebuild the Image for Your Architecture To build the image locally for linux/amd64, use the following commands:

docker build --platform linux/amd64 -t lishan2023/calculator-app:latest .

Run the newly built image:

sudo docker run -p 8080:8080 lishan2023/calculator-app:latest

Force Docker to Use the Correct Platform You can tell Docker to specifically pull or run the image for the linux/amd64 platform, even if the image was originally built for linux/arm64. Use the --platform flag to specify the architecture.

Run the following command to force Docker to use the linux/amd64 architecture:

sudo docker run --platform linux/amd64 -p 8080:8080 lishan2023/calculator-app:latest

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Finally, Deploy the application onto the GKE Kubernetes cluster: using Deployment and Service Manifest file.