The Publisher and Subscriber APIs in a Reactor

The previous chapter provided you with a brief introduction to the evolution of the reactive paradigm. In that chapter, we discussed how Reactive Streams enable us to perform reactive modeling in imperative languages, such as Java. We also discussed the key components in reactive—the publisher and subscriber. In this chapter, we will cover these two components in detail. Since Reactive Streams is a specification, it does not provide any implementations of the two components. It only lists the responsibilities of the individual components. It is left to implementation libraries, such as Reactor, to provide concrete implementations for the interfaces. Reactor also provides different methods for instantiating publisher and subscriber objects.

 We will cover the following topics in this chapter:

• Comparing streams to existing Java APIs
• Understanding the Flux API
• Understanding the Mono API
• Building subscribers to Flux and Mono publishers