Table Of ContentHands-On Reactive
Programming in Spring 5
Build cloud-ready, reactive systems with Spring 5
and Project Reactor
Oleh Dokuka
Igor Lozynskyi
BIRMINGHAM - MUMBAI
Hands-On Reactive Programming in
Spring 5
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In the memory of my father, Ivan
– Igor Lozynskyi
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Foreword
Reactive programming is finally getting the attention it deserves with the help of famous
Java names such as Spring Boot and Spring Framework. Which qualifier would you use to
describe Spring solutions? The usual answer I hear and read from various
users—pragmatic. The reactive support offered is no exception, and the team has chosen to
keep supporting both reactive and non-reactive stacks. With choice comes responsibility, it
is, therefore, critical to understand when to design your application "the reactive way" and
what best practices you can apply to your next production-ready systems.
Spring positions itself as a provider of the best tooling available to write all kinds of
microservices. With its reactive stack, Spring helps developers to create incredibly efficient,
available, and resilient endpoints. As a byproduct, reactive Spring microservices tolerate
network latency and cope with failure in a much less impacting way. Think about it—it's
the right solution if you are writing an Edge API, a mobile backend, or a heavily
mutualized microservice! The secret? Reactive microservices isolate slow transactions and
reward the fastest.
Once you have qualified your needs, Project Reactor will be a reactive foundation of choice
that will naturally pair with your reactive Spring project. In its latest 3.x iterations, it
implements most of the Reactive extensions described first by Microsoft in 2011. Along
with a standard vocabulary, Reactor introduces first-class support for Reactive Streams
flow control at every functional stage and unique features such as Context passing.
In a synthetic but not simplistic set of example-driven chapters, Oleh and Igor describe a
fantastic journey into reactive programming and reactive systems. After a quick context
setting, reminding the history and challenges of Project Reactor, we quickly dive into
ready-to-use examples running on Spring Boot 2. The book never does miss an occasion to
seriously cover testing, giving a clear idea on how to produce quality reactive code.
Oleh and Igor perfectly introduce their readers to those reactive design patterns for the
scalability needs of today and tomorrow. The authors cover more than reactive
programming with plenty of guidance on Spring Boot or Spring Framework. In a forward-
looking chapter, authors stimulate the readers' curiosity with some details about reactive
communications using RSocket—a promising technology poised to deliver reactive benefits
to the transport layer.
I hope you will take as much pleasure from reading this book as I did and keep learning
new ways of writing applications.
Stéphane Maldini
Lead developer, Project Reactor
Contributors
About the authors
Oleh Dokuka is an experienced software engineer, Pivotal Champion, and one of the top
contributors to Project Reactor and Spring Framework. He knows the internals of both
frameworks very well and advocates reactive programming with Project Reactor on a daily
basis. Along with that, the author applies Spring Framework and Project Reactor in
software development, so he knows how to build reactive systems using these technologies.
Igor Lozynskyi is a senior Java developer who primarily focuses on developing reliable,
scalable, and blazingly fast systems. He has over seven years of experience with the Java
platform. He is passionate about interesting and dynamic projects both in life and in
software development.
About the reviewers
Mikalai Alimenkou is a senior delivery manager, Java tech lead, and experienced coach.
An expert in Java development, scalable architecture, agile engineering practices, QA
processes, and project management, he has more than 14 years of development experience,
specializes in complex, distributed, scalable systems, and global company transformations.
He's an active participant and speaker at many international conferences and is the founder
and an independent consultant at XP Injection—a training and consulting provider. He's an
organizer and founder of Selenium Camp, JEEConf, and XP Days Ukraine international
conferences, as well as the Active Anonymous Developers Club (UADEVCLUB).
Nazarii Cherkas works as a solutions architect at Hazelcast—a company that develops
open source projects such as Hazelcast IMDG and Hazelcast Jet. Nazarii has many years of
experience of working in different positions, from Java engineer to team lead. He has been
involved in various projects for different industries, from telecoms and healthcare to critical
systems serving the infrastructure of one of world's biggest airlines. He holds a master's
degree in computer science of the Yuriy Fedkovych Chernivtsi National University.
Tomasz Nurkiewicz is a Java champion. He had spent half of his life programming. On a
daily basis, he works in the e-commerce sector. He's involved in open source, is DZone's
most valuable blogger, and used to be very active on Stack Overflow. He's an author,
trainer, conference speaker, technical reviewer, and runner. He claims that code that's not
tested automatically is not a feature but just a rumor. He also wrote a book on RxJava.
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Table of Contents
Preface 1
Chapter 1: Why Reactive Spring? 6
Why reactive? 6
Message-driven communication 10
Reactivity use cases 15
Why Reactive Spring? 19
Reactivity on the service level 20
Summary 29
Chapter 2: Reactive Programming in Spring - Basic Concepts 30
Early reactive solutions in Spring 30
Observer pattern 31
Observer pattern usage example 35
Publish-Subscribe pattern with @EventListener 38
Building applications with @EventListener 40
Bootstrapping a Spring application 41
Implementing business logic 42
Asynchronous HTTP with Spring Web MVC 43
Exposing the SSE endpoint 44
Configuring asynchronous support 45
Building a UI with SSE support 46
Verifying application functionality 47
Criticism of the solution 48
RxJava as a reactive framework 49
Observer plus iterator equals Reactive Stream 50
Producing and consuming streams 52
Generating an asynchronous sequence 55
Stream transformation and marble diagrams 56
Map operator 56
Filter operator 57
Count operator 58
Zip operator 59
Prerequisites and benefits of RxJava 60
Rebuilding our application with RxJava 63
Implementing business logic 63
Custom SseEmitter 65
Exposing the SSE endpoint 66
Application configuration 67
Brief history of reactive libraries 68
Reactive landscape 69
Summary 72
