How to use "cache" method of Mono

Question

I'm a beginner of spring webflux. While researching I found some code like:

Mono result = someMethodThatReturnMono().cache();

The name "cache" tell me about caching something, but where is the cache and how to retrieve cached things? Is it something like caffeine?

Answer 1

It cache the result of the previous steps of the Flux/Mono until the cache() method is called, check the output of this code to see it in action:

import reactor.core.publisher.Mono;

public class CacheExample {

    public static void main(String[] args) {
        var mono = Mono.fromCallable(() -> {
            System.out.println("Go!");
            return 5;
        })
        .map(i -> {
            System.out.println("Double!");
            return i * 2;
        });

        var cached = mono.cache();

        System.out.println("Using cached");

        System.out.println("1. " + cached.block());
        System.out.println("2. " + cached.block());
        System.out.println("3. " + cached.block());

        System.out.println("Using NOT cached");


        System.out.println("1. " + mono.block());
        System.out.println("2. " + mono.block());
        System.out.println("3. " + mono.block());
    }
}

output:

Using cached
Go!
Double!
1. 10
2. 10
3. 10
Using NOT cached
Go!
Double!
1. 10
Go!
Double!
2. 10
Go!
Double!
3. 10