FIX Protocol Trading Simulator

A self-contained FIX 4.4 trading simulator built with QuickFIX/J and Spring Boot 3.

Submit orders via REST API → they are routed over a live FIX 4.4 session to a mock exchange running inside the same JVM → execution reports update order state asynchronously in real time.

Architecture

 REST Client (curl / Swagger UI / Postman)
        │
        │  HTTP POST /api/orders
        ▼
 ┌─────────────────────────────────────────────────────────┐
 │                  Spring Boot Application                 │
 │                                                         │
 │  OrderController ──► OrderService ──► OrderRepository   │
 │                           │              (ConcurrentHashMap)
 │                           │ sendNewOrderSingle()
 │                           ▼
 │            ┌─────────────────────────┐
 │            │       FixClient         │  FIX Initiator
 │            │   (QuickFIX/J)          │  SenderCompID: CLIENT
 │            └────────────┬────────────┘  Port: 9878
 │                         │
 │           FIX 4.4 NewOrderSingle (MsgType=D)
 │                         │
 │            ┌────────────▼────────────┐
 │            │  MockExchangeAcceptor   │  FIX Acceptor
 │            │   (QuickFIX/J)          │  SenderCompID: EXCHANGE
 │            └────────────┬────────────┘  Port: 9878
 │                         │
 │     FIX 4.4 ExecutionReport (MsgType=8)
 │        OrdStatus=NEW  → then → OrdStatus=FILLED
 │                         │
 │            ┌────────────▼────────────┐
 │            │       FixClient         │
 │            │   fromApp() callback    │
 │            └────────────┬────────────┘
 │                         │ updateOrderStatus()
 │                         ▼
 │                   OrderService
 │                   OrderRepository
 └─────────────────────────────────────────────────────────┘

Features

Feature	Details
FIX 4.4 Protocol	Full session management, heartbeats, logon/logout
NewOrderSingle	Place LIMIT and MARKET orders
OrderCancelRequest	Cancel open orders
ExecutionReport	Asynchronous fill simulation (NEW → FILLED)
REST API	4 endpoints with full Swagger/OpenAPI documentation
In-memory Order Book	Thread-safe `ConcurrentHashMap` with dual indexing
Docker	Multi-stage build, single `docker-compose up` to run
Tests	37 tests — repository, service, controller and integration layers
Actuator	`/actuator/health`, `/actuator/metrics` endpoints

Prerequisites

Tool	Version	Notes
Java (JDK)	17 or later	Download Temurin 17
Maven	3.8+	Bundled with Eclipse (m2e)
Docker Desktop	24+	Only needed for Docker run
Eclipse IDE	2023-09+	With m2e plugin (bundled)

Quick Start — Docker (recommended)

No Java installation required. One command.

# 1. Clone the repository
git clone https://github.com/RIDHVI07/fix-trading-simulator.git
cd fix-trading-simulator

# 2. Build and run
docker-compose up --build

# 3. Open Swagger UI in your browser
open http://localhost:8080/swagger-ui.html

Expected startup output:

fix-trading-simulator  | MockExchangeAcceptor started on port 9878
fix-trading-simulator  | FixClient initiator started — connecting to localhost:9878
fix-trading-simulator  | FIX session logged on: FIX.4.4:CLIENT->EXCHANGE
fix-trading-simulator  | Started TradingSimulatorApplication in 4.2 seconds

Stop the container:

docker-compose down

Quick Start — Eclipse

Step 1 — Import the project

Open Eclipse IDE
Go to File → Import → Maven → Existing Maven Projects
Click Browse → navigate to the cloned fix-trading-simulator folder
Click Finish
Eclipse will automatically download all Maven dependencies (this takes ~2 minutes on first import)

Tip: If you see red error markers, right-click the project → Maven → Update Project → check Force Update of Snapshots/Releases → OK.

Step 2 — Run the application

In Package Explorer, expand src/main/java
Navigate to com.trading.simulator
Right-click TradingSimulatorApplication.java
Select Run As → Java Application
Watch the Console tab — you should see:

MockExchangeAcceptor started on port 9878
FixClient initiator started
FIX session logged on: FIX.4.4:CLIENT->EXCHANGE
Started TradingSimulatorApplication in 4.x seconds

Step 3 — Open Swagger UI

Navigate to: http://localhost:8080/swagger-ui.html

Quick Start — Maven CLI

# Clone
git clone https://github.com/RIDHVI07/fix-trading-simulator.git
cd fix-trading-simulator

# Build
mvn clean package -DskipTests

# Run
mvn spring-boot:run

API Reference

Once running, the full interactive API is available at:

http://localhost:8080/swagger-ui.html

Endpoints

Method	Endpoint	Description
`POST`	`/api/orders`	Place a new order
`GET`	`/api/orders`	List all orders (optional `?symbol=AAPL` filter)
`GET`	`/api/orders/{orderId}`	Get order by ID
`DELETE`	`/api/orders/{orderId}`	Cancel an open order

Place a LIMIT order

curl -X POST http://localhost:8080/api/orders \
  -H "Content-Type: application/json" \
  -d '{
    "symbol":   "AAPL",
    "side":     "BUY",
    "type":     "LIMIT",
    "quantity": 100,
    "price":    150.50
  }'

Response 201 Created:

{
  "orderId":   "3f7a2b1c-...",
  "symbol":    "AAPL",
  "side":      "BUY",
  "type":      "LIMIT",
  "quantity":  100,
  "filledQty": 0,
  "price":     150.50,
  "status":    "PENDING",
  "createdAt": "2025-05-08T14:30:01"
}

After ~2 seconds, polling GET /api/orders/{orderId} will show:

{
  "status":        "FILLED",
  "filledQty":     100,
  "avgFillPrice":  150.50
}

Place a MARKET order

curl -X POST http://localhost:8080/api/orders \
  -H "Content-Type: application/json" \
  -d '{
    "symbol":   "TSLA",
    "side":     "SELL",
    "type":     "MARKET",
    "quantity": 50
  }'

List all orders

curl http://localhost:8080/api/orders

# Filter by symbol
curl "http://localhost:8080/api/orders?symbol=AAPL"

Cancel an order

curl -X DELETE http://localhost:8080/api/orders/{orderId}

FIX Message Flow

Client (FixClient)                    Exchange (MockExchangeAcceptor)
      |                                           |
      |──── Logon (MsgType=A) ──────────────────►|
      |◄─── Logon (MsgType=A) ─────────────────── |
      |                                           |
      |  [POST /api/orders]                       |
      |──── NewOrderSingle (D) ─────────────────►|
      |         ClOrdID=CLO-123                   |  Validates order
      |         Symbol=AAPL                       |
      |         Side=1 (BUY)                      |
      |         OrdType=2 (LIMIT)                 |
      |         Price=150.50                      |
      |         OrderQty=100                      |
      |                                           |
      |◄─── ExecutionReport (8) ──────────────── |
      |         OrdStatus=0 (NEW)                 |  Acknowledged
      |         CumQty=0                          |
      |         LeavesQty=100                     |
      |                                           |
      |       [~2 seconds later]                  |
      |◄─── ExecutionReport (8) ──────────────── |
      |         OrdStatus=2 (FILLED)              |  Fully filled
      |         CumQty=100                        |
      |         AvgPx=150.50                      |
      |                                           |

Running Tests

# Run all tests
mvn test

# Run a specific test class
mvn test -Dtest=OrderServiceTest

# Run with coverage report
mvn verify

Test coverage summary:

Layer	Test Class	Tests
Repository	`OrderRepositoryTest`	10 tests
Service	`OrderServiceTest`	16 tests
Controller	`OrderControllerTest`	10 tests
Integration	`TradingSimulatorApplicationTests`	1 test
Total		37 tests

Project Structure

fix-trading-simulator/
├── src/
│   ├── main/java/com/trading/simulator/
│   │   ├── TradingSimulatorApplication.java   # Entry point
│   │   ├── config/
│   │   │   └── OpenApiConfig.java             # Swagger configuration
│   │   ├── controller/
│   │   │   └── OrderController.java           # REST endpoints
│   │   ├── dto/
│   │   │   ├── PlaceOrderRequest.java         # Inbound request body
│   │   │   └── OrderResponse.java             # Outbound response body
│   │   ├── fix/
│   │   │   ├── FixClient.java                 # FIX initiator (CLIENT side)
│   │   │   └── MockExchangeAcceptor.java      # FIX acceptor (EXCHANGE side)
│   │   ├── model/
│   │   │   ├── Order.java
│   │   │   ├── OrderSide.java                 # BUY | SELL
│   │   │   ├── OrderStatus.java               # PENDING → NEW → FILLED
│   │   │   └── OrderType.java                 # MARKET | LIMIT
│   │   ├── repository/
│   │   │   └── OrderRepository.java           # Thread-safe in-memory store
│   │   └── service/
│   │       └── OrderService.java              # Business logic
│   ├── main/resources/
│   │   └── application.properties
│   └── test/java/com/trading/simulator/
│       ├── TradingSimulatorApplicationTests.java
│       ├── controller/
│       │   └── OrderControllerTest.java
│       ├── repository/
│       │   └── OrderRepositoryTest.java
│       └── service/
│           └── OrderServiceTest.java
├── Dockerfile                                 # Multi-stage build
├── docker-compose.yml
├── pom.xml
└── README.md

Configuration Reference

All properties are in src/main/resources/application.properties and can be overridden via environment variables.

Property	Default	Description
`server.port`	`8080`	HTTP server port
`fix.acceptor.port`	`9878`	FIX session port (acceptor listens here)
`fix.initiator.host`	`localhost`	Host the initiator connects to
`fix.fill.delay.seconds`	`2`	Seconds before exchange sends FILLED report

Override via environment variable (Docker):

environment:
  - fix.fill.delay.seconds=5

Tech Stack

Component	Technology
Language	Java 17
Framework	Spring Boot 3.2.5
FIX Engine	QuickFIX/J 2.3.1
FIX Version	FIX 4.4
API Docs	SpringDoc OpenAPI 2.3 (Swagger UI)
Build	Maven 3.8+
Container	Docker + Docker Compose
Testing	JUnit 5, Mockito, MockMvc

Author

Ridhvi Kulshrestha — Backend Developer · Java & Spring Boot · Electronic Trading Systems

Email: ridhvikul07@gmail.com
LinkedIn: linkedin.com/in/ridhvi-kulshrestha
GitHub: github.com/RIDHVI07

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FIX Protocol Trading Simulator

Table of Contents

Architecture

Features

Prerequisites

Quick Start — Docker (recommended)

Quick Start — Eclipse

Step 1 — Import the project

Step 2 — Run the application

Step 3 — Open Swagger UI

Quick Start — Maven CLI

API Reference

Endpoints

Place a LIMIT order

Place a MARKET order

List all orders

Cancel an order

FIX Message Flow

Running Tests

Project Structure

Configuration Reference

Tech Stack

Author

About

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LICENSE		LICENSE
README.md		README.md
docker-compose.yml		docker-compose.yml
pom.xml		pom.xml

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FIX Protocol Trading Simulator

Table of Contents

Architecture

Features

Prerequisites

Quick Start — Docker (recommended)

Quick Start — Eclipse

Step 1 — Import the project

Step 2 — Run the application

Step 3 — Open Swagger UI

Quick Start — Maven CLI

API Reference

Endpoints

Place a LIMIT order

Place a MARKET order

List all orders

Cancel an order

FIX Message Flow

Running Tests

Project Structure

Configuration Reference

Tech Stack

Author

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