Ktor + Koin + Exposed Example

Source code accompanying the blog post series on softwaremill.com:

• Part 1: Bootstrap Your Backend Server Using Ktor, Koin, and Exposed

A Trading Accountability App — a tool that logs trades, enforces trading rules, and flags violations when discipline slips. Built with Kotlin-native libraries only.

Stack

• Kotlin 2.3.20
• Ktor 3.4.1 — HTTP server framework
• Koin 4.1.1 — Dependency injection
• Exposed 1.2.0 — Type-safe SQL
• H2 — In-memory database
• Gradle 9.4.1, JDK 25 (LTS)

Run

./gradlew run

The server starts at http://localhost:8080.

API Endpoints

Health check

curl http://localhost:8080/health

{"status": "UP"}

Create a trading rule

curl -X POST http://localhost:8080/rules \
  -H "Content-Type: application/json" \
  -d '{"name": "Always add notes", "description": "Every trade must have notes explaining the rationale"}'

{"id": 1, "name": "Always add notes", "description": "Every trade must have notes explaining the rationale"}

List all rules

curl http://localhost:8080/rules

Open a trade

curl -X POST http://localhost:8080/trades \
  -H "Content-Type: application/json" \
  -d '{"ticker": "BTC/USD", "direction": "LONG", "entryPrice": "67000.00", "quantity": "0.5"}'

{"id": 1, "ticker": "BTC/USD", "direction": "LONG", "entryPrice": "67000.0000", "quantity": "0.5000", "openedAt": "2026-04-02T10:48:54"}

Close a trade

Closing a trade automatically checks active trading rules and logs any violations:

curl -X PUT http://localhost:8080/trades/1/close \
  -H "Content-Type: application/json" \
  -d '{"exitPrice": "68500.00", "notes": "Target hit"}'

Get a trade (with violations)

curl http://localhost:8080/trades/1

List all trades

curl http://localhost:8080/trades

Log a violation manually

curl -X POST http://localhost:8080/trades/1/violations \
  -H "Content-Type: application/json" \
  -d '{"ruleId": 1, "description": "Entered without checking higher timeframe"}'

Repo Tags

The repo is tagged by article progression:

• v0 — Minimal runnable scaffold: Ktor + Koin + Exposed configured, health endpoint only
• v1 — You are here. Complete implementation from Part 1: full CRUD, trading rules, violation detection

Project Structure

src/main/kotlin/com/trading/
├── Application.kt              — Entry point (fun main)
├── config/
│   ├── Database.kt             — H2 connection + schema creation
│   ├── Koin.kt                 — DI module definitions
│   ├── Serialization.kt        — JSON content negotiation
│   └── StatusPages.kt          — Error handlers → HTTP status codes
├── db/
│   └── Tables.kt               — Exposed table definitions
├── model/
│   ├── Models.kt               — Domain models + request DTOs
│   └── BigDecimalSerializer.kt — Custom serializer for financial precision
├── repository/                 — Data access layer (interface + Exposed implementation)
├── routes/                     — HTTP endpoint definitions
└── service/                    — Business logic with transaction management