Kotlin REST API Application

A modern, containerized Kotlin web application built with Ktor framework, featuring three REST API endpoints and a beautiful responsive HTML UI for interacting with the APIs.

🚀 Features

• Three REST API Endpoints:

  • GET /api/greeting - Returns a personalized greeting with timestamp
  • POST /api/calculate - Performs arithmetic operations (add, subtract, multiply, divide)
  • GET /api/time - Returns current server time and timezone information

• Responsive Web UI:

  • Modern, gradient-based design with glassmorphism effects
  • Fully responsive (mobile and desktop)
  • Interactive forms to test each API endpoint
  • Real-time result display with smooth animations

• Containerized:

  • Docker support for easy deployment
  • Multi-stage build for optimized image size
  • Platform-specific build support (linux/amd64)

🛠️ Technology Stack

• Language: Kotlin 1.9.21
• Framework: Ktor 2.3.7
• Build Tool: Gradle 8.5
• Runtime: OpenJDK 17
• Server: Netty (embedded)

📋 API Endpoints

1. Greeting API

GET /api/greeting?name=YourName

Response:

{
  "message": "Hello, YourName! Welcome to Kotlin REST API.",
  "timestamp": "2025-12-19T16:50:01+05:30"
}

2. Calculator API

POST /api/calculate
Content-Type: application/json

{
  "operation": "add",
  "a": 10,
  "b": 5
}

Response:

{
  "result": 15.0,
  "operation": "add",
  "expression": "10.0 + 5.0 = 15.0"
}

Supported operations: add, subtract, multiply, divide

3. Server Time API

GET /api/time

Response:

{
  "currentTime": "2025-12-19 16:50:01",
  "timezone": "Asia/Kolkata",
  "epochMillis": 1734609601000
}

🐳 Docker Instructions

Building the Docker Image

Build the Docker image for linux/amd64 platform:

docker build --platform=linux/amd64 -t kotlin-docker-app .

This will:

1. Use Gradle to build the application
2. Create a fat JAR with all dependencies
3. Package it in a lightweight OpenJDK 17 runtime image

Running the Container

Run the container and map port 9000:

docker run -p 9000:9000 kotlin-docker-app

For running in detached mode:

docker run -d -p 9000:9000 --name kotlin-api kotlin-docker-app

Accessing the Application

Once the container is running, access the application at:

• Web UI: http://localhost:9000
• API Endpoints:
  • http://localhost:9000/api/greeting?name=Test
  • http://localhost:9000/api/calculate (POST)
  • http://localhost:9000/api/time

💻 Local Development

Prerequisites

• JDK 17 or higher
• Gradle 8.5 or higher (or use the Gradle wrapper)

Running Locally

1. Build the application:

./gradlew build

2. Run the application:

./gradlew run

The application will start on port 9000.

Testing the APIs

Using curl:

# Test greeting endpoint
curl "http://localhost:9000/api/greeting?name=Developer"

# Test calculator endpoint
curl -X POST http://localhost:9000/api/calculate \
  -H "Content-Type: application/json" \
  -d '{"operation":"multiply","a":7,"b":6}'

# Test time endpoint
curl http://localhost:9000/api/time

📱 UI Features

The web interface provides:

• Beautiful gradient background with purple-to-violet theme
• Glassmorphism cards for each API endpoint
• Interactive forms with real-time validation
• Smooth animations and hover effects
• Responsive design that works on all screen sizes
• JSON response display with proper formatting

🔧 Project Structure

kotlin-docker/
├── src/
│   └── main/
│       └── kotlin/
│           └── com/
│               └── example/
│                   └── Application.kt
├── build.gradle.kts
├── settings.gradle.kts
├── Dockerfile
└── README.md

📝 License

This project is open source and available for educational and commercial use.