All the code used in this chapter can be downloaded from the following GitHub link: https://github.com/PacktPublishing/Spring-5.0-Projects/tree/master/chapter02. The code can be executed on any operating system, although it has only been tested on Windows.

The word reactive has become popular today and has different meanings for different people, such as lightweight, real time, asynchronous, streaming, and so on. Reactive, in broader terms, refers to a set of design techniques or principles, and is a way to consider the system architecture in a distributed environment. It comprises tooling, design methodologies, and implementation procedures. 

The analogy of a team can be used to describe a reactive system: individual players working with each other to achieve a desired goal. The interaction between the components is the main quality that differentiates a Reactive System from other systems. Components can operate individually or still work in harmony with others to achieve the intended result as a whole system. In other words, it is the system design that allows individual sub-applications to form...

Reactive Programming can be used to build a Reactive System. By definition, Reactive Programming is a programming practice or pattern that is aligned around the data flow and the propagation of the changes. The changes in data are automatically propagated by the underlying execution model through the data flow. 

To make it simple, Reactive Programming is a way to handle asynchronous data streams in a more effective manner. In other words, it is programming dealing with an asynchronous data stream, or it can be called the subset of asynchronous programming. Reactive Programming is a way of execution where new information will push the flow forward, rather than having the flow controlled by an execution thread.

The data stream is a series of business events that happen during the system execution, such as various keyboard or mouse events, HTML field...

An asynchronous processing approach is a perfect fit while dealing with a huge volume of data or a large set of users. It will make the system responsive and improve the overall user experience. Implementing asynchronous processing in Java with the custom code would be cumbersome and harder to implement. Reactive Programming would be beneficial in this scenario.

Java doesn't provide native support for Reactive Programming like other JVM-based programming languages such as Scala or Clojure do. However, from version 9, Java has started supporting Reactive Programming natively. Apart from native support in Java 9, there are other implementation layers that help to achieve Reactive Programming with an older version of Java (such as Java 8). We will see a few of them, as follows.

Spring is a modular framework and used to build every aspect of an application from the web to the persistence layer. Each module is considered as a sub-framework and targeted for a specific area of development. For example, to support a web layer with a servlet API,  the Spring MVC module was included in the Spring Framework. 

Similarly, to support a reactive stack in the web layer, Spring WebFlux was introduced in Spring Framework 5. It is fully non-blocking, backpressure, asynchronous, and compliant with Reactive Streams specifications. It can be run on Servlet 3.1+, Netty, and Undertow containers.

Spring Framework has both the stacks, Spring Web MVC and spring-WebFlux, and developers are free to use either of them, or in some scenarios to mix both of them to develop a Spring-based web application. The typical example...

We will create a sample web application with the WebFlux framework. The application will simply access existing student information from a data store. Instead of making a fully fledged application, we will focus more on how to access data in a reactive manner with the WebFlux framework.

We will use Spring Boot to kickstart the development. For those who are new to Spring Boot, it is a tool and part of Spring Horizon, which is designed to speed up and simplify the bootstrapping and development of new Spring-based applications.

You might have come across bulky XML and other configurations repeatedly in Spring projects. The Spring team was well aware of this and has finally developed a tool called Spring Boot, aimed at freeing the developer from providing a boilerplate configuration, which is not only tedious but time consuming.

We will create...

Reactive is definitely a promising new technology that will help to build a scalable and high-performance application. Spring has done an impressive job of supporting Reactive Systems with a new framework called WebFlux. Reactive is the future of next-generation applications, and it is needed almost everywhere: datastores, middle layers, frontends, or even mobile platforms.

Through this chapter, we learned the basics of Reactive Systems and Reactive Programming followed by various techniques to achieve it. We then learned about Reactive Streams, which is one of the most popular ways of implementing a Reactive System. Starting with the Reactive Streams specifications and the basic fundamentals, we explored various JVM-based libraries that provide an implementation for a particular specification. We did some hands-on work with RxJava and Project Reactor and learned the underlying...