ddd-cqrs-4-java-example

Example microservices that use ddd-4-java and cqrs-4-java libraries and an EventStore to store the events (Event Sourcing). Supports Quarkus and Spring Boot.

Background

This application shows how to implement DDD, CQRS and Event Sourcing without a DDD/CQRS framework. It uses just a few small libraries in addition to standard web application frameworks like Quarkus and Spring Boot.

If you are new to the DDD/CQRS topic, you can use these mindmaps to find out more:

• DDD Mindmap
• CQRS Mindmap

Here is an overview of how such an application looks like:

Components

• Shared - Common code for all demo applications (commands, events, value objects and utilities).
• Aggregates - DDD related code for all demo applications (aggregates, entities and business exceptions).
• Quarkus - Two microservices (Command & Query) based on Quarkus that is the successor of Wildfly Swarm/Thorntail and has CDI, JAX-RS and SmallRye (Eclipse MicroProfile).
• Spring Boot - Two microservices (Command & Query) based on Spring Boot.
• Java SE + CDI - Two standalone applications (Command & Query) using CDI for dependency injection.

Getting started

Prerequisites

Option 1: Install everything yourself

Make sure you have the following tools installed/configured:

• git (VCS)
• Docker CE
• Docker Compose
• OPTIONAL GraalVM
• Hostname should be set in /etc/hosts (See Find and Change Your Hostname in Ubuntu for more information)

⭐ Option 2: Use lubuntu-developer-vm ⭐

The lubuntu-developer-vm has already (almost) everything installed. You only need to execute the following steps:

1. Download and install the lubuntu-developer-vm as described
2. OPTIONAL: Change memory of VM to 6 GB (instead of 4 GB default) if you want to create a native image with GraalVM
3. Start the VM and login (developer / developer)
4. Open a console (Shortcut = ctrl alt t)
5. Run a script that finalizes the setup of the developer virtual machine

   bash <(curl \
   -s https://raw.githubusercontent.com/fuinorg/ddd-cqrs-4-java-example/master/setup-lubuntu-developer-vm.sh)   
   

6. Reboot

   reboot
   

Clone and install project

1. Open a console (Ubuntu shortcut = ctrl alt t)
2. Clone the git repository

   git clone https://github.com/fuinorg/ddd-cqrs-4-java-example.git
   

3. Change into the project's directory and run a Maven build

   cd ddd-cqrs-4-java-example
   ./mvnw install
   

   Be patient - This may take a while (~5 minutes) as all dependencies and some Docker images must be downloaded and also some integration tests will be executed.

Start Event Store and Maria DB

1. Open a console (Ubuntu shortcut = ctrl alt t)
2. Change into the project's directory and run Docker Compose

   cd ddd-cqrs-4-java-example
   docker-compose up
   

Start command / query implementations

Start one command microservice and one query microservice - You can mix Quarkus & Spring Boot!

Quarkus Microservices

Module
Command
Query

Spring Boot Microservices

Module
Command
Query

Test

1. Open http://localhost:2113/ to access the event store UI (User: admin / Password: changeit) You should see a projection named "qry-person-stream" when you click on "Projections" in the top menu.
2. Opening http://localhost:8080/persons should show an empty JSON array
3. Open a console (Ubuntu shortcut = ctrl alt t)
4. Change into the demo directory and execute a command using cURL (See shell script and command)

   cd ddd-cqrs-4-java-example/demo
   ./create-person-command.sh
   

   Command console should show something like

   Update aggregate: id=PERSON 84565d62-115e-4502-b7c9-38ad69c64b05, version=-1, nextVersion=0
   

   Query console should show something like

   PersonCreatedEventHandler ... Handle PersonCreatedEvent: Person 'Peter Parker' was created
   

5. Refreshing http://localhost:8080/persons should show

   [{"id":"84565d62-115e-4502-b7c9-38ad69c64b05","name":"Peter Parker"}]
   

6. Opening http://localhost:8080/persons/84565d62-115e-4502-b7c9-38ad69c64b05 should show

   {"id":"84565d62-115e-4502-b7c9-38ad69c64b05","name":"Peter Parker"}
   

7. The event sourced data of the person aggregate could be found in a stream named PERSON-84565d62-115e-4502-b7c9-38ad69c64b05

Stop Event Store and Maria DB and clean up

1. Stop Docker Compose (Ubuntu shortcut = ctrl c)
2. Remove Docker Compose container

   docker-compose rm