Reactive Stock/Crypto Tracker

Real-time stock and cryptocurrency price tracker built with reactive stack.

Architecture

┌──────────────────────────────────────────────────────┐
│                    Clients                            │
│          REST API          SSE Stream                 │
└──────────┬──────────────────┬────────────────────────┘
           │                  │
┌──────────▼──────────────────▼────────────────────────┐
│              Spring WebFlux (Netty)                   │
│     StockRouter → StockHandler → StockService         │
└──────────┬──────────────────────────────────────────┘
           │
     ┌─────▼─────┐         ┌────────────────┐
     │  R2DBC    │         │  Reactor Kafka  │
     │ PostgreSQL│◄────────│   Consumer      │
     └───────────┘         └───────┬────────┘
                                   │
                           ┌───────▼────────┐
                           │  Kafka Topic    │
                           │  stock-prices   │
                           └───────┬────────┘
                                   │
                           ┌───────▼────────┐
                           │ PriceProducer   │
                           │  (scheduled)    │
                           └──┬──────────┬──┘
                              │          │
                    ┌─────────▼┐   ┌─────▼──────┐
                    │ Tinkoff  │   │  CoinGecko  │
                    │ API      │   │  API        │
                    │ SBER,GAZP│   │  BTC, ETH   │
                    └──────────┘   └─────────────┘

Tech Stack

Layer	Technology
Runtime	Java 17, Spring Boot 3.4
Web	Spring WebFlux (Netty), functional routing
Database	R2DBC PostgreSQL, Liquibase migrations
Messaging	Reactor Kafka (producer/consumer)
HTTP Client	WebClient (reactive, non-blocking)
Testing	JUnit 5, Mockito, StepVerifier, Testcontainers
Infra	Docker Compose (PostgreSQL 16 + Kafka)

Data Sources

• Tinkoff API — Russian stocks (SBER, GAZP, LKOH, YNDX), free API
• CoinGecko API — Cryptocurrencies (BTC, ETH), free API

Quick Start

# Start infrastructure
docker-compose up -d

# Run application
./gradlew bootRun

# Open dashboard
open http://localhost:8080

# Or use API directly
curl http://localhost:8080/api/stocks
curl -N http://localhost:8080/api/stocks/stream  # SSE live prices

API Endpoints

Method	Path	Description
GET	/api/stocks	List all tracked stocks
GET	/api/stocks/{symbol}	Get stock by symbol
POST	/api/stocks	Add stock to track
DELETE	/api/stocks/{symbol}	Remove stock
GET	/api/stocks/stream	SSE stream — all prices
GET	/api/stocks/{symbol}/prices/stream	SSE stream — single stock
GET	/api/stocks/{symbol}/prices?limit=50	Price history

Testing

./gradlew test

Test Class	Type	What it covers
StockServiceTest	Unit	CRUD operations, StepVerifier + Mockito
StockHandlerTest	WebFlux	Handlers with WebTestClient
PriceFlowIntegrationTest	E2E	Full flow with Testcontainers (PostgreSQL + Kafka)

Key Patterns

• Functional routing — RouterFunction + HandlerFunction instead of @RestController
• SSE streaming — Flux<T> + MediaType.TEXT_EVENT_STREAM for real-time updates
• Reactive Kafka — non-blocking producer/consumer with Project Reactor
• StepVerifier — testing reactive streams step by step
• Constructor injection — explicit DI, no @Autowired

License

MIT