Hands-on Examples on Advanced Beginner

Project Setup

d8lzz1gpw@mozmail.com (kimbenji) — Tue, 13 Jan 2026 00:00:00 +0000

Project Setup#

TL;DR

DDD layered architecture (Domain, Application, Infrastructure, Interfaces) package structure

Spring Boot 3.2.x + Spring Kafka + JPA based dependencies

AggregateRoot, DomainEvent, Entity base class implementations

Docker Compose for Kafka + PostgreSQL development environment

Target Audience and Prerequisites#

Item	Required Level
Target Audience	Backend developers looking to apply DDD patterns with Spring Boot
Java	Java 17+ syntax, Record, Stream API
Spring Boot	Spring Boot basics, DI, @Service, @Repository
Gradle	Kotlin DSL basic syntax
Docker	Experience running docker-compose up/down

Setting up the structure and dependencies for the DDD example project.

Order Domain

d8lzz1gpw@mozmail.com (kimbenji) — Tue, 13 Jan 2026 00:00:00 +0000

Order Domain Implementation#

TL;DR

Order: Aggregate Root. Manages the order’s consistency boundary

OrderLine: Internal Entity. Can only be created/modified through Order

Money, ShippingAddress, OrderId: Value Objects. Immutable and compared by value

Invariants: At least 1 order line, max amount 100M won, quantity 1~999

Domain Events: OrderCreatedEvent, OrderConfirmedEvent, etc. published on state changes

Target Audience and Prerequisites#

Item	Required Level
Target Audience	Developers implementing DDD tactical patterns in code
DDD Basics	Understanding of Aggregate, Entity, Value Object, Domain Event concepts
Java	Experience with Record, Optional, Stream API
Prerequisite	Project Setup completed

Implementing the order domain with DDD patterns.

Application Layer

d8lzz1gpw@mozmail.com (kimbenji) — Tue, 13 Jan 2026 00:00:00 +0000

Application Layer Implementation#

TL;DR

OrderService: Use Case orchestration. Calls domain logic, manages transactions, publishes events

Command objects: Encapsulate requests as immutable objects like CreateOrderCommand

DTO: Separate response representation from domain with OrderResponse, etc.

JPA Repository: Implementation of Domain Repository interface. Uses Mapper for Entity conversion

Event handler: Publishes to Kafka after commit using @TransactionalEventListener

Target Audience and Prerequisites#

Item	Required Level
Target Audience	Developers learning Application Service and Infrastructure layer implementation
Spring	Experience with @Service, @Transactional, @Repository annotations
JPA	Understanding of Entity, @Embedded, CascadeType
Prerequisites	Project Setup, Order Domain completed

Implementing Application Services that orchestrate use cases and the infrastructure layer.

Event Sourcing Practice

d8lzz1gpw@mozmail.com (kimbenji) — Tue, 13 Jan 2026 00:00:00 +0000

TL;DR

Event Sourcing: Store events instead of state. Restore state by replaying events

Event Store: Persistent storage for events. Version-based optimistic concurrency control

Event-Sourced Aggregate: Apply/when pattern for event application and state changes

Snapshot: Periodically save state snapshots for performance optimization

Point-in-time Recovery: Replay events up to a specific version to query past state

Target Audience and Prerequisites#

Item	Required Level
Target Audience	Developers looking to implement the Event Sourcing pattern
DDD	Understanding of Aggregate and Domain Event concepts
Java	Switch Expression, Pattern Matching syntax
Prerequisites	Order Domain, Application Layer completed

Implement the Event Sourcing pattern for an order domain. Store events instead of state, and restore state by replaying events.