Reactor – Simple Ways to create Flux/Mono

Reactive Streams is an API and pattern that provides a standard for asynchronous stream processing with non-blocking back pressure. It is also being introduced in Java 9 Flow API with four simple interfaces: Publisher, Subscriber, Subscription and Processor.

But Reactive Streams API is just low level to make practical use in reactive applications. So Reactor Core provides two main implementations of Publisher: Flux and Mono. In this tutorial, we’re gonna know what they are and simple ways to create them.

I. Overview

For more details about Reactive Streams and Publish-Subscribe Pattern, please visit:
Java 9 Flow API – Reactive Streams

1. Flux & Mono

A Flux<T> is a standard Publisher<T> representing a reactive sequence of 0..N items, optionally terminated by either a success signal or an error.

While Mono<T> is a specialized Publisher<T> that emits at most single-valued-or-empty result.

2. Simple ways to create Publishers with Flux and Mono
2.1 Mono

Empty Mono:

– Mono with value:

– Mono that emits an Exception:

2.2 Flux

Empty Flux:

– Flux with items:

– Flux from Collections:

– Flux that is infinite and ticks every x units of time with an increasing Long:

– Flux that emits an Exception:

II. Practice

0. Technology

– Java 8
– Maven 3.6.1
– Reactor Core 3.0.4, with the Aluminium release train.

1. Reactor installation in Maven

– First, import the BOM by adding the following to pom.xml:

– Next, add dependency:

2. Write Code

3. Run & Check Result


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