Event Sourcing REST API Demo application using Java / Spring / Axon / Mongo. This application demonstrates how to implement a RESTful API with Event Sourcing, CQRS and DDD principles. This will allow for capturing events and appending these to the event history. In doing this, we are able to load past events and replay history to build the latest snapshot of data.
In addition, by implementing the API using CQRS principles, we can split the write (Command) from the read (Query) phases. This means that data being written in the system utilizes a separate path from the querying side. To name a few advantages for this, we would be able to performance tune the path that is more frequently used by for instance using a faster Database for the busier side.
Mongo DB was used as the database for the read and write models, primarily for its speed annd being a document database, writing documents requires little transformation logic from Java objects.
Finally, Axon was used in order to facilitate the event sourced and CQRS design of this application. The primary benefit of using such a framework is that this will handle the event store required for event sourcing. In addition, this will encourage using DDD principles.
In order to develop this app, a docker-compose file was added to host Mongo and Axon.
Step 1) Download docker desktop from https://www.docker.com/products/docker-desktop/
Step 2) Run the app
The app uses the Maven for dependency management. Using the Maven wrapper (MVNW), you do not need to install Maven to run the app.
Command to run from the top level of the project:
./mvnw spring-boot:run
Step 3) enable axon server node
Go to http://localhost:8024/ ensure that "Start as standalone node or first node" is selected and select Finish in the form to initialize the node for a fresh installation.
After a short while the app should connect to the Axon server and become available for REST requests,
Run the following command:
./mvnw test