Currency Exchange Service

A Spring Boot microservice that provides a REST API for fetching, storing, and converting currency exchange rates using live data from an external API. This project demonstrates a complete end-to-end workflow, from project setup to production-ready API.

---

🚀 Features

• Fetch & Store Rates: Retrieve live exchange rates from the ExchangeRate API and persist them in an H2 database.
• Retrieve Latest Rate: Query the most recently stored rate for any currency pair.
• Convert Amounts: Convert monetary values using the latest stored rate.
• Error Handling: Returns meaningful HTTP status codes (400, 404, 201, 200).
• Configuration-Driven: Externalize API keys and database settings in application.yml.
• Auto-Configuration & Starters: Leverage Spring Boot’s auto-configuration and starter dependencies for rapid development.
• Postman Collection: Includes a ready-to-import collection to test all endpoints and error scenarios.

---

📂 Project Structure

currency-exchange-app/
├── src/main/java/com/drill/currencyexchangeapp/
│   ├── controller/       # REST controllers
│   ├── service/          # Service interfaces & implementations
│   ├── repository/       # Spring Data JPA repositories
│   ├── model/            # JPA entity classes
│   └── dto/              # External API response mappings
├── src/main/resources/
│   └── application.yml   # Application configuration (DB, API keys, etc.)
├── src/test/java/        # Unit tests for service layer
├── pom.xml               # Maven build file (dependencies & plugins)
└── README.md             # Project documentation

---

⚙️ Getting Started

Prerequisites

• Java 8+
• Maven 3.6+
• (Optional) IDE: IntelliJ IDEA, Eclipse, VS Code

Installation

1. Clone the repository

   git clone https://github.com/your-username/springboot-currency-exchange-service-backend.git
   cd springboot-currency-exchange-service-backend

2. Obtain and configure your API key

   1. Sign up for a free key at ExchangeRate API.

   2. In your account dashboard, copy your API Key.

   3. Open src/main/resources/application.yml and replace YOUR_API_KEY:

      exchange:
        api:
          url: https://v6.exchangerate-api.com/v6  # Base URL for all requests
          key: <YOUR_API_KEY>                     # ← Paste your key here

   4. Verify you can fetch live rates:

      curl https://v6.exchangerate-api.com/v6/$YOUR_API_KEY/latest/USD

   exchange:
     api:
       url: https://v6.exchangerate-api.com/v6
       key: YOUR_API_KEY   # Replace with your key from ExchangeRate API

3. Build & run the application

   mvn clean install
   mvn spring-boot:run

4. Access H2 Console (for database exploration)

   • URL: http://localhost:8080/h2-console
   • JDBC URL: jdbc:h2:mem:currencydb
   • User: sa, Password: (leave blank)

---

📡 API Endpoints

Method	Endpoint	Description
GET	/api/ping	Health check, returns pong.
POST	/api/rates/fetch?from={from}&to={to}	Fetches live rate, stores it, returns entity.
GET	/api/rates/latest?from={from}&to={to}	Returns the most recently stored rate.
GET	/api/convert?from={from}&to={to}&amount=	Converts the amount using the stored rate.

Error Responses:

• 400 Bad Request: Invalid or unsupported currency codes.
• 404 Not Found: No rate stored for the specified currency pair.

---

🛠️ Testing

1. Unit Tests

   mvn test

2. Postman Collection

   • Import postman/ExchangeRateService.postman_collection.json to execute happy-path and error-case scenarios.

---

🔑 Skills & Technologies

• Java 8+: BigDecimal, Instant, Java 8 streams
• Spring Boot: Auto-configuration, starter dependencies, embedded Tomcat
• Spring Data JPA: Entity mapping, CRUD, custom finder methods
• Hibernate: ORM, schema generation, transaction management
• WebClient: Reactive HTTP client for external API integrations
• H2 Database: In-memory persistence for rapid development
• REST API Design: Controllers, validation, HTTP status codes
• Error Handling: Custom exceptions, @ControllerAdvice
• Maven: Dependency & build management, plugins
• Testing: JUnit 5, Mockito, Spring Boot Test
• API Documentation: Postman collections for endpoint validation