In the previous chapter, we learned the essentials of Project Reactor, as well as the behavior of reactive types and operators and how they help to solve different business problems. Along with the straightforward API, we saw that, under the hood, there are hidden complex mechanisms that allow concurrent, asynchronous, nonblocking message processing. In addition to this, we explored available backpressure controls and related strategies. As we saw in the previous chapter, Project Reactor is more than just a reactive programming library. It also offers add-ons and adapters that make it possible to build reactive systems, even without the Spring Framework. Through this, we saw an integration of Project Reactor with Apache Kafka and Netty.

While Project Reactor may work well without Spring Framework, it is usually not enough to build a feature-rich application. One of the missing elements here is the well-known dependency injection, which gives us decoupling between components. Moreover, the time when we build powerful and customizable applications is when Spring Framework shines more brightly. However, even better applications may be built with Spring Boot.

Consequently, in this chapter, we are going to describe the importance of Spring Boot and the features that it brings. We are also going to see the changes that come with Spring Framework 5 and Spring Boot 2, looking at how the Spring ecosystem adopts the reactive programming approach.

This chapter covers the following topics:

• The problems Spring Boot solves, and how
• The essentials of Spring Boot
• Reactivity in Spring Boot 2.0 and Spring Framework