Functional programming marks a shift from traditional imperatives to a more declarative style of programming. Reactive programming builds on top of functional programming to provide an alternative style.

In this chapter, we will discuss the basics of reactive programming.

The microservice architecture promotes message-based communication. One important tenet of reactive programming is building applications around events (or messages). Some of the important questions we will look at in this chapter include the following:

• What is reactive programming?
• What are the typical use cases?
• What kind of support does Java provide for it?
• How does Spring support reactive programming?
• What are the reactive features in Spring WebFlux?