Example Java DDD/CQRS/Event Sourcing microservices with Quarkus, Spring Boot and the EventStore from Greg Young. The code uses the lightweight ddd-4-java and cqrs-4-java libaries. No special framework is used except the well known JEE/Spring standards.

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:

• 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.

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)

1. Clone the git repository

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

2. 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.

Change into the project's directory and run Docker Compose

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

Start one query service and then one command service. You can mix Quarkus & Spring Boot if you want to!

1. Start the Quarkus query service:

   cd ddd-cqrs-4-java-example/quarkus/query
   ./mvnw quarkus:dev
   

2. Opening http://localhost:8080/ should show the query welcome page

For more details see quarkus/query.

1. Start the Quarkus command service:

   cd ddd-cqrs-4-java-example/quarkus/command
   ./mvnw quarkus:dev
   

2. Opening http://localhost:8081/ should show the command welcome page

For more details see quarkus/command.

1. Start the Spring Boot query service:

   cd ddd-cqrs-4-java-example/spring-boot/query
   ./mvnw spring-boot:run
   

2. Opening http://localhost:8080/ should show the query welcome page

For more details see spring-boot/query.

1. Start the Spring Boot command service:

   cd ddd-cqrs-4-java-example/spring-boot/command
   ./mvnw spring-boot:run
   

2. Opening http://localhost:8081/ should show the command welcome page

For more details see spring-boot/command.

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

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 service (Console window 3) should show something like

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

Query service (Console window 2) should show something like

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

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

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

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

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

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

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

   docker-compose rm