In this chapter, we will explore one of the most important features of the Spring 5 Framework, which is reactive pattern programming. The Spring 5 Framework introduced this new feature with the Spring web reactive module. We will discuss this module in this chapter. Before that, let's have a look at reactive patterns. What is the reactive pattern, and why is it growing more popular nowadays? I will start my discussion on reactive pattern with the following statement made by Satya Nadella, CEO, Microsoft Corporation:

The topics we will cover here are as follows:

• Why reactive pattern?
• The reactive pattern principles
• Blocking calls
• Non-blocking calls
• Back-pressure
• Implementing the reactive pattern using the Spring Framework
• The Spring web reactive module