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:

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.
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

Install everything yourself (Option 1)

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)

Use lubuntu-developer-vm (Option 2)

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

Download and install the lubuntu-developer-vm as described
OPTIONAL: Change memory of VM to 6 GB (instead of 4 GB default) if you want to create a native image with GraalVM
Start the VM and login (developer / developer)
Open a console (Shortcut = ctrl alt t)

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)

Reboot
```
reboot
```

Clone and install project

Open a console (Ubuntu shortcut = ctrl alt t)

Clone the git repository

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

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

Open a console (Ubuntu shortcut = ctrl alt t)
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

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.
Opening http://localhost:8080/persons should show an empty JSON array
Open a console (Ubuntu shortcut = ctrl alt t)

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

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

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

Opening http://localhost:8080/persons/84565d62-115e-4502-b7c9-38ad69c64b05 should show
```
{"id":"84565d62-115e-4502-b7c9-38ad69c64b05","name":"Peter Parker"}
```
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

Stop Docker Compose (Ubuntu shortcut = ctrl c)
Remove Docker Compose container
```
docker-compose rm
```