Reactive development became a trending topic in many developers conferences, meetups, blog posts, and other countless content sources (both online and offline).

But what is a reactive application? Well, there's a official definition of it contained in something called The Reactive Manifesto (please refer to https://www.reactivemanifesto.org for more details).

In short, according to the manifesto, reactive systems are:

• Responsive: The system responds in a timely manner if at all possible
• Resilient: The system stays responsive in the face of failure
• Elastic: The system stays responsive under varying workloads
• Message driven: Reactive systems rely on asynchronous message-passing to establish a boundary between components that ensures loose coupling, isolation, and location transparency

So, this chapter will show you how to use Java EE 8 features to meet one or more of those reactive system requirements.