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Real-Time Currency Converter Web Application

This is a high-performance, responsive web application built with Java 23 and Spring Boot 4.0.5. It provides real-time currency exchange rates, interactive market trend graphs, and a secure user environment.

🚀 Key Features

  • User Authentication: Secure Registration and Login system powered by Spring Security.
  • Real-Time Dashboard: Displays live exchange rates for top global currencies (USD, EUR, GBP, PKR, etc.).
  • Interactive Charts: Visualizes market trends using Chart.js for a modern, data-driven experience.
  • Surgical Converter: A dedicated tool for instant currency conversion with a one-click "Swap" feature.
  • High Performance Caching: Implements Caffeine Cache with a 6-hour TTL (Time-To-Live) to ensure lightning-fast responses and resilient API usage.
  • Responsive Design: Fully mobile-friendly UI built with Vanilla CSS and Thymeleaf fragments.

🛠️ Technology Stack

  • Backend: Java 23, Spring Boot 4.0.5, Spring Data JPA.
  • Security: Spring Security (Form-based Auth).
  • Database: H2 (In-memory, for rapid development and user management).
  • External API: ExchangeRate-API (v6).
  • Frontend: Thymeleaf, Vanilla CSS, Chart.js.
  • Client: Spring's modern RestClient.

📂 Project Structure

src/main/java/com/example/realtime_currency_converter/
├── config/        # Security and App configuration
├── controller/    # Web Controllers (Auth, Dashboard, Converter)
├── model/         # JPA Entities and API DTOs (Records)
├── repository/    # Database access layers
└── service/       # Business logic & External API Client

⚙️ How It Works

1. Security Flow

Users must register and log in to access the dashboard. We use BCryptPasswordEncoder for secure password storage in the H2 database.

2. API Integration & Caching

The ExchangeRateClient uses Spring's RestClient to fetch JSON data from the ExchangeRate-API. To avoid hitting API rate limits and to ensure < 100ms response times, we use @Cacheable.

  • Cache Strategy: Data is stored in-memory for 6 hours. If the API is down, the system remains stable by serving cached data.

3. Data Visualization

On the Dashboard, we fetch the top 10 world currencies. This data is passed to the frontend and rendered as a Line Chart using Chart.js, allowing users to see the relative strength of currencies at a glance.

🚦 Getting Started

Prerequisites

  • JDK 23
  • Maven 3.9+

Configuration

The API key is already configured in src/main/resources/application.yaml:

app:
  exchange-rate-api:
    key: put your api key 
    key is avilable at https://www.exchangerate-api.com/

Running the App

  1. Open your terminal in the project root.
  2. Run: ./mvnw spring-boot:run
  3. Access the app at: http://localhost:8080
  4. H2 Console: Access the database at http://localhost:8080/h2-console (JDBC URL: jdbc:h2:mem:currency_db).

🛡️ Future Enhancements

  • Historical data persistence for 30-day trend analysis.
  • Multi-currency conversion (convert to 5 currencies at once).
  • Geolocation to automatically detect local currency.

Developed as a modern utility for travelers, expatriates, and business professionals.