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Rohit is an investor, startup advisor and an Application Modernization Scale Specialist working at Google.

Wednesday, October 26, 2016

CQRS and Event Sourcing in Java with Spring Framework

Recently I have had the opportunity to delve deep in to the world of Event Sourcing and CQRS for a modernization project where we are refactoring a 1M LOC a decade old classic java application that does more than a billion dollars of revenue across multiple lines of business. If you have to embark on a similar journey these are the resources I found useful:

1. DDD Distilled : This is the best summary of the classic Eric Evan's DDD book and Vernon's iDDD book. There is also a more practical Tools and Techniques section which summarizes Event Storming technique very well. We used a 3 day event storming inception to discover the complex business and technical domain and figure out the bounded contexts and problem areas.

2. Event Storming from Alberto Brandolini: A very easy read on the why and how of event storming. Alberto's writing style is very entertaining. This is probably the most interesting book written in this space. Alberto and Paul Raynor's videos(1, 2) on event storming provide a good getting-started guide to the world of event storming.

3. This Gist from Szymon provides an excellent collection of videos to understand the basics of modeling, Domain-Driven Design, CQRS and Event Sourcing.

4. Online Class: Greg Young's entire Domain Driven Design, CQRS, and Event Sourcing class all online.

5. Read Event Sourcing and CQRS chapter from Cloud Native Go: Building Web Applications and Microservices for the Cloud with Go and React on Safari Online.

6. Can't say enough good things about Michael Ploed's talk on building microservices with event sourcing and CQRS at SpringOne 2016. His practical advice is sorely needed in understanding the production concerns when refactoring a monolith to event-sourcing.

7. Peruse significant discussions on the DDD CQRS Group google mailing list.

8. Blogs & Articles

9. Code Repositories:

10. Videos & Webinars:


  1. Great list of resources.

    I recently came across this one from a CapitalOne engineer: https://github.com/capitalone/cqrs-manager-for-distributed-reactive-services/blob/master/doc/rationale.md#context-and-references . It's not about Spring, but it's a great resource about ES/CQRS. That has links to a presentation that he gave about the concept at Strange Loop and some other great presentations like Rich Hickey's "value of values" talk from 2012.

  2. Great collection of resources here! Have you encountered any deep dive examples of event sourcing with a real domain model? There's a wealth of general, conceptual information out there about cqrs and event sourcing but I'd love to explore a real world example with all the finicky requirements of a real domain.