Reactor - Creating Flux and Mono with empty()

Following are empty() methods of Flux and Mono to create their empty instances which complete without emitting any item.

Flux method

public static <T> Flux<T> empty()

Mono method

public static <T> Mono<T> empty()

Examples

package com.logicbig.example;

import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

public class FluxMonoJustExamples {
    public static void main(String[] args) {
        System.out.println("-- Flux#empty example --");
        Flux.empty()
            .subscribe(System.out::println);

        System.out.println("-- Mono#empty example --");
        Mono.empty()
            .subscribe(System.out::println);
    }
}

-- Flux#empty example --
-- Mono#empty example --

Since Flux/Mono don't allow null items, Flux#empty() and Mono#empty() can be useful where we need to handle null situation, examples:

package com.logicbig.example;

import reactor.core.publisher.Flux;

public class FluxEmptyExample1 {

    public static void main(String[] args) {
        if (args.length != 0) {
            process(Flux.just(args[0]));
        } else {
            process(Flux.empty());
        }
    }

    private static void process(Flux<String> flux) {
        flux.map(n -> n.length())
            .subscribe(System.out::println);
    }
}

package com.logicbig.example;

import reactor.core.publisher.Flux;

public class FluxEmptyExample2 {

    public static void main(String[] args) {
        process(args.length != 0 ? args[0] : null)
                .subscribe(System.out::println);
    }

    private static Flux<Integer> process(String i) {
        if (i == null) {
            return Flux.empty();
        } else {
            return Flux.just(i)
                       .map(String::length);
        }
    }
}

Example Project

Dependencies and Technologies Used:

• reactor-core 3.3.10.RELEASE: Non-Blocking Reactive Foundation for the JVM.
• JDK 8
• Maven 3.5.4