Reactive Streams

Reactive Streams is an initiative that aims to standardize asynchronous stream processing with non-blocking backpressure in the Java ecosystem. It provides a common API and set of rules for working with asynchronous data streams in a reactive manner, enabling interoperability between different reactive libraries and components. The Reactive Streams specification defines the contract between publishers and subscribers to ensure proper handling of backpressure and asynchronous data flow.

Key Components of Reactive Streams:

1. Publisher:

   • A publisher is a source of asynchronous data emissions.
   • It implements the org.reactivestreams.Publisher interface.
   • Key Methods:
     • subscribe(Subscriber<? super T> subscriber): Subscribes the given subscriber to the publisher. The subscriber will start receiving data emissions and other signals from the publisher.

2. Subscriber:

   • A subscriber consumes data emitted by a publisher asynchronously.
   • It implements the org.reactivestreams.Subscriber interface.
   • Key Methods:
     • onSubscribe(Subscription subscription): Receives a subscription from the publisher. The subscriber can use this subscription to request data from the publisher or cancel the subscription.
     • onNext(T item): Receives the next item emitted by the publisher.
     • onError(Throwable throwable): Receives an error signal from the publisher.
     • onComplete(): Receives a completion signal from the publisher, indicating that no more items will be emitted.

3. Subscription:

   • A subscription represents the relationship between a publisher and a subscriber.
   • It implements the org.reactivestreams.Subscription interface.
   • Key Methods:
     • request(long n): Requests the publisher to emit up to n items to the subscriber. This method is used by subscribers to control the rate of data emission and implement backpressure.
     • cancel(): Cancels the subscription, indicating that the subscriber is no longer interested in receiving data from the publisher.

Reactive Streams Specification:

The Reactive Streams specification defines the following rules and requirements:

• Asynchronous and Non-Blocking: Publishers and subscribers must operate asynchronously without blocking threads. All operations, including data emission, processing, and consumption, should be performed asynchronously to avoid thread contention and improve system responsiveness.

• Backpressure: Publishers must respect the backpressure signals sent by subscribers to control the rate of data emission. They should only emit items when requested by subscribers and apply backpressure mechanisms to prevent overwhelming subscribers with data.

• Error Handling: Publishers must notify subscribers of any errors encountered during data processing and propagate error signals downstream. Subscribers should handle errors appropriately and may choose to terminate the subscription upon encountering an error condition.

• Completion Signaling: Publishers must signal completion to subscribers after emitting the entire data stream successfully. They should send a completion signal downstream to indicate that no more items will be emitted. Subscribers should handle completion signals and perform any necessary cleanup or finalization actions.

By adhering to these rules and requirements, Reactive Streams implementations ensure consistent behavior and interoperability across different reactive libraries and components in the Java ecosystem. This enables developers to build reactive applications with asynchronous stream processing and non-blocking backpressure, making them more responsive, scalable, and resilient to failures.