[Update] Following our Reactor 2.5 introduction, we shifted the version to 3.0 to reflect better the major redesign effort overtaken.

A meaningful composition API

The former reactor-stream module has been merged into Reactor Core 3.0. Flux and Mono respectively representing 0..N and 0..1 sequence types now cover a solid range of operations for the following categories:

• Cold-to-Hot or Multicasting : publish, publishNext, cache, multicast...
• Aggregating/Reducing (Transforming) : buffer, reduce, scan, window, sample...
• Filtering : filter, exists, single...
• Conditioning : timeout, take, takeUntil, skip, skipUntil...
• Combining : withLatestFrom, combineLatest
• Backpressuring : onBackpressureDrop, onBackpressureLatest...
…

Entering Reactive Streams Era

Reactor 2.0 development started by the end of 2014, around the same time as Reactive Streams. We were keen on joining the effort and early adopt a backpressure protocol to mitigate our main message-passing limitation: bounded capacity. We delivered in Reactor 2.0 the first attempt to make Reactive Streams implementations of RingBuffer-based schedulers and derived an increasingly popular reactive pattern: Reactive Extensions.

Meanwhile, Reactive Streams started getting traction and an entire ecosystem of libraries discussed this transition. The regular concern ? Implementing Reactive Streams semantics is all but an easy task. We observed an increasing need for a reactive foundation to solve message-passing and implement common streaming operators. We therefore created a dedicated project space for Reactor Core and started a focused effort with Spring Framework team…