Book Image

Reactive Programming in Kotlin

By : Rivu Chakraborty
Book Image

Reactive Programming in Kotlin

By: Rivu Chakraborty

Overview of this book

In today's app-driven era, when programs are asynchronous, and responsiveness is so vital, reactive programming can help you write code that's more reliable, easier to scale, and better-performing. Reactive programming is revolutionary. With this practical book, Kotlin developers will first learn how to view problems in the reactive way, and then build programs that leverage the best features of this exciting new programming paradigm. You will begin with the general concepts of Reactive programming and then gradually move on to working with asynchronous data streams. You will dive into advanced techniques such as manipulating time in data-flow, customizing operators and provider and how to use the concurrency model to control asynchronicity of code and process event handlers effectively. You will then be introduced to functional reactive programming and will learn to apply FRP in practical use cases in Kotlin. This book will also take you one step forward by introducing you to Spring 5 and Spring Boot 2 using Kotlin. By the end of the book, you will be able to build real-world applications with reactive user interfaces as well as you'll learn to implement reactive programming paradigms in Android.
Table of Contents (20 chapters)
Title Page
About the Author
About the Reviewers
Customer Feedback

The error handling operators

We already learned about the onError event in the Subscriber/Observer. However, the problem with the onError event is that the error is emitted to the downstream consumer chain, and the subscription is terminated instantly. For example, take a look at the following program:

    fun main(args: Array<String>) { 
       .map { it.toIntOrError() } 
       .subscribeBy ( 
           onNext = { 
              println("Next $it") 
           onError = { 
              println("Error $it") 

The output of the program is shown in the following screenshot:

The program throws an exception in the map operator when the string Errr is emitted from the Observable. The exception was caught by the onError handler, but the Subscription doesn't get any further emissions.

This may not be the desired behavior every time. Although we cannot pretend the error never happened and continue...