Adam L. Davis

Reactive Streams in JavaConcurrency with RxJava, Reactor, and Akka Streams

Adam L. Davis

Oviedo, FL, USA

Any source code or other supplementary material referenced by the author in this book is available to readers on GitHub via the book’s product page, located at www.​apress.​com/​9781484241752 . For more detailed information, please visit http://​www.​apress.​com/​source-code .

ISBN 978-1-4842-4175-2e-ISBN 978-1-4842-4176-9

https://doi.org/10.1007/978-1-4842-4176-9

Library of Congress Control Number: 2018965180

© Adam L. Davis 2019

This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed.

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While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein.

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Preface

Who Is the Target Audience?

This book is intended for Java developers of beginning or intermediate skill who wish to learn more about reactive programming. If you are still reading this, then that probably means you!

Why You Should Read This Book

You should read this book to learn the basic of reactive programming with Reactive Streams and understand what they are good for, when they should be used, and the principles behind them. This book uses straightforward examples and introduces concepts gradually so as not to overwhelm the reader. It will refer to existing models of concurrency from time to time only as reference points and will not assume any advanced knowledge on the topic.

After reading this book, you should have a firm understanding of Reactive Streams, including three different implementations, and how to integrate them into real software projects. You will understand when to use Reactive Streams, how to write tests, and how to build a whole project.

What Is Not in This Book

This book assumes you have a basic background of programming in Java, so it will not cover the basics.

For more of an introduction on basic Java concepts, please check out my other books: Modern Programming Made Easy, Modern Java, and What’s New in Java 8 .

Table of Contents

Chapter 1:​ Introduction to Reactive Streams 1

Java 9+ 2

Flow 2

Code for This Book 3

Chapter 2:​ Existing Models of Concurrency in Java 5

Prominent Models for Concurrency 5

Synchronize in Java 6

Java Futures 6

Drawbacks of the Future Interface 7

CompletableFutur​e 7

STM in Clojure 10

Actors 11

Groovy GPars 12

Reactive Streams 12

Chapter 3:​ Common Concepts 15

Streams 15

Hot and Cold 15

Backpressure 16

Filter 16

Any/​All 17

Map 18

FlatMap/​ConcatMap 18

Delay 19

Buffer 19

Window 20

Take While 21

Latest 22

Debounce 22

Throttle First 23

Chapter 4:​ RxJava 25

Getting Started 25

Flowable 26

Parallel Computing 27

Schedulers 28

Publishers 30

Backpressure 34

Handling Errors 36

Testing 37

Chapter 5:​ Reactor 41

Getting Started 41

Flux 42

Mono 43

Creating a Flux or Mono 44

Schedulers 46

Pull Events 49

Handling Backpressure 50

Context 51

Testing 53

StepVerifier 53

TestPublisher 55

Chapter 6:​ Akka Streams 57

Getting Started 58

ActorMaterialize​r 60

Sinks, Flows, and Graphs 61

Backpressure 64

Interoperation with Reactive Streams API 64

MergeHub, BroadcastHub, and PartitionHub 65

Testing 66

Chapter 7:​ Android and RxJava 71

Getting Started 71

Android SDK 74

Android Schedulers 75

RxBinding 76

RxLifecycle 78

Putting It Together 80

Using RxJava 81

Testing 81

Chapter 8:​ Spring Boot and Reactor 83

Getting Started 83

Gradle Plugin 84

Tasks 86

SpringBootApplic​ation 87

Auto-Configuration 88

Our Domain Model 89

ReactiveMongoRep​ository 90

Controllers 92

View Templates 94

Restful API 95

Further Configuration 98

Testing 102

Chapter 9:​ Akka HTTP and Akka Streams 105

Getting Started 106

Routes 110

WebSockets 112

Our Domain 114

Our Repository 115

ChatServer 115

MergeHub and Publisher 117

The WebSocket Flow 118

The Web Client 122

Testing 125

Chapter 10:​ Conclusions 129

RxJava 129

Reactor 130

Akka Streams 130

Conclusion 130

Appendix A:​ Java 10 and 11 131

Local Variable Types 131

Lambda Expression Local Variable Types 133

Index 135

About the Author and About the Technical Reviewer

About the Author

Adam L. Davis

(@adamldavis ) makes software. He’s spent many years developing in Java (since Java 1.2) and has enjoyed using Spring and Hibernate. Since 2006 he’s been using Groovy and Grails in addition to Java to create SaaS web applications that help track finances for large institutions (among other things). Adam has a master’s and a bachelor’s degree in computer science from Georgia Tech. For more, visit http://adamldavis.com .

 

About the Technical Reviewer

Manuel Jordan Elera

is an autodidactic developer and researcher who enjoys learning new technologies for his own experiments and creating new integrations. Manuel won the Springy Award – Community Champion and Spring Champion 2013. In his little free time, he reads the Bible and composes music on his guitar. Manuel is known as dr_pompeii. He has tech reviewed numerous books for Apress, including Pro Spring, 4th Edition (2014); Practical Spring LDAP (2013); Pro JPA 2, Second Edition (2013); and Pro Spring Security (2013). Read his 13 detailed tutorials about many Spring technologies, contact him through his blog at www.manueljordanelera.blogspot.com , and follow him on his Twitter account, @dr_pompeii .