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The Reactive Manifesto

You might have heard about the Reactive Manifesto, a document that describes a set of principles for designing reactive systems.

These systems have the following characteristics:

  • Responsiveness. The system must provide fast and consistent response times.
  • Resilience. The system must stay responsive even after failure.
  • Elasticity. The system must stay responsive even after increasing workload.
  • Message-driven. The system uses asynchronous messages for communication between its components.

But, as you can see, it’s an architectural style. It’s different from reactive programming.

You can build a reactive system without using reactive programming as long as the system is designed with the principles described above.

Yes, messages and events are both, non-blocking and asynchronous, but they refer to different things and operate at different levels of abstraction.

A message is some data (usually an object) sent to a particular address. In this case, a message broker like Apache Kafka or RabbitMQ is in charge of the communication.

On the other hand, events in reactive programming are actions or data from a source (a publisher) that the subscribers react to asynchronously using callbacks, futures, or libraries like Reactor that also offer a declarative/functional API.

In summary, reactive programming means programming in a non-blocking, asynchronous way.

With this out of the way, let’s introduce Project Reactor and set up a demo project.