Adam L. Davis - 2019

Reactive Streams is an initiative to provide a standard for asynchronous stream processing with non-blocking back pressure. This encompasses efforts aimed at runtime environments (JVM and JavaScript) as well as network protocols.

reactive-streams.org

At their core, Reactive Streams are an effort to provide highly responsive applications able to handle many requests per second with the ability to manage backpressure (the ability to skip or queue data that is coming too fast to be processed). Asynchronous means processing can take place in many threads, without stopping to read data from a file or a web request for example. Although many implementations already exist for asynchronous processing, such as Javas Future, CompletableFuture, and parallel streams, most of them do not have standard support for asynchronous handling of backpressure.

Reactive Streams are a unifying standard that abstracts existing methods of concurrency. Also, by having one standard, different Reactive Streams implementations can interoperate in one application.

Java 9 was an important release of Java and includes Project Jigsaw which represents a huge restructuring of the core JDK (Java Development Kit ) as well as a new and improved way of defining code dependencies. This provides compile-time errors when dependencies are missing as opposed to runtime errors, which is a vast improvement for software development efficiency. Java 9 also introduced a unified interface for Reactive Streams.