What is reactive programming?

Reactive programming is a paradigm focused on data streams and the propagation of change. It is based on the idea of transmitting signals, which represent events or data, between system components.

Main concepts:

• Data Streams: A sequence of events or values that occur over time.
• Observers: Objects that subscribe to data streams and react to the events occurring within them.
• Publishers / Observables: Objects that generate data streams and notify observers of new events.
• Operators: Functions that transform, combine, or filter data streams.

Advantages:

• Scalability: Easier to handle a large number of parallel requests or data.
• Reactivity: The system responds quickly to events and changes.
• Resilience: The system remains operational even when failures occur in one of the components.
• Elasticity: The system can dynamically adapt to changing loads.
• Ease of composing asynchronous operations: Allows for more declarative descriptions of complex asynchronous scenarios.

Popular libraries and frameworks in Java:

• RxJava
• Project Reactor
• Vert.x

A simple example using Project Reactor:

import reactor.core.publisher.Flux;

public class ReactiveExample {
    public static void main(String[] args) {
        Flux.just("Apple", "Banana", "Cherry") // Create a data stream
            .map(String::toUpperCase) // Transform elements to uppercase
            .filter(s -> s.startsWith("B")) // Filter elements starting with "B"
            .subscribe( // Subscribe to the stream and output elements
                item -> System.out.println("Received: " + item),
                error -> System.err.println("Error: " + error),
                () -> System.out.println("Completed")
            );
    }
}