ddd-java

Preface

This is a DDD sample implementation using Spring Boot.
It is not a framework, but a simple example of implementation based on Evans's DDD.

This approach is straightforward and based on Evans's book, rather than verbose approaches like Clean Architecture or Hexagonal Architecture.

Concept of Layering

This follows the famous three-layer model, but considers the infrastructure layer as a cross-cutting concern.

Layer
UI	Receives use case requests
Application	Use case processing (including external resource access)
Domain	Pure domain logic (does not depend on external resources)
Infrastructure	DI container, ORM, and various libraries

Usually, the UI layer handles public interactions using Thymeleaf, but this sample assumes the use of different types of clients and only provides APIs through RESTful endpoints.

Spring Boot Usage Policy

Spring Boot can be used in various ways, but this sample follows the following policies:

• Use standard configurations as much as possible, such as DB settings.
• Configuration files use YAML. XML files are not used for Bean definitions.
• Exception handling is defined at endpoints (RestErrorAdvice).

Java Coding Policy

• Java 21 or higher
• Use Lombok actively to reduce boilerplate code.
• Keep names as brief as possible.
• Do not overuse interfaces.
• DTOs that are part of the domain are defined as inner classes.

Resource Structure

Refer to the following for the package and resource structure:

main
  java
    sample
      context                         … Infrastructure Layer
      controller                      … UI Layer
      model                           … Domain Layer
      usecase                         … Application Layer
      util                            … Utilities
      - Application.java              … Bootstrap
  resources
    - application.yml                 … Spring Boot Configuration
    - messages-validation.properties  … Validation Message Resources
    - messages.properties             … Label Message Resources

Use Case

Consider the following as a sample use case:

• A customer with an account balance requests a withdrawal. (Event T, Delivery T + 3)
• The system closes the withdrawal request. (Allows cancellation of the request until closing)
• The system advances the business day to the next day.
• The system reflects the cash flow on the delivery date to the account balance.

Getting Started

This sample uses Gradle. You can check the operation easily with an IDE or console.

Server Start (VSCode DevContainer)

The following steps are required:

• Ensure Docker is installed.
• Ensure VSCode with DevContainer Extension is installed.

Prepare this sample with the following steps:

1. Navigate to the cloned ddd-java directory.
2. Run the command code ..
3. Choose Open Container.

Start the server with the following steps:

1. Open VSCode "Run And Debug".
2. Choose Run ddd-java.
3. If the console shows "Started Application", the server has started on port 8080.
4. Run the command curl http://localhost:8080/actuator/health.

Server Start (Console)

Run the application from a Windows/Mac console using Gradle.

The following steps are required:

• Ensure JDK 21+ is installed.

Start the server with the following steps:

1. Navigate to the cloned ddd-java directory.
2. Run the command ./gradlew bootRun --args='--spring.profiles.active=dev'.
3. If the console shows "Started Application", the server has started on port 8080.
4. Run the command curl http://localhost:8080/actuator/health.

Check Use Case

After launching the server on port 8080, you can test the RESTful API execution by accessing the following URLs from the console:

Customer Use Case

• curl -X POST -H "Content-Type: application/json" -d '{"accountId" : "sample" , "currency" : "JPY", "absAmount": 1000}' http://localhost:8080/asset/cio/withdraw
  • Request a withdrawal.
• curl 'http://localhost:8080/asset/cio/unprocessedOut'
  • Search for outstanding withdrawal requests.

Internal Use Case

• curl 'http://localhost:8080/admin/asset/cio?updFromDay=yyyy-MM-dd&updToDay=yyyy-MM-dd'
  • Search for deposit and withdrawal requests.
  • Please set actual dates for upd*Day parameters.

Batch Use Case

• curl -X POST http://localhost:8080/system/job/daily/closingCashOut
  • Close withdrawal requests.
• curl -X POST http://localhost:8080/system/job/daily/processDay
  • Advance the business day to the next day.
• curl -X POST http://localhost:8080/system/job/daily/realizeCashflow
  • Realize cash flow. (Reflects to the balance on the delivery date)

Please execute these according to the business day appropriately.

License

The license for this sample code is MIT License. Use it as a base implementation when starting a project using Spring Boot.