FluxfromIterable

Flux.fromIterable is a static factory method in the Reactor Core library that creates a Flux which emits the elements of a supplied Iterable. The emitted items appear in the same order as provided by the Iterable's iterator, and the sequence completes after the last element is emitted.

The publisher is cold, meaning each subscriber triggers a fresh iteration over the input Iterable. It is also backpressure-aware, emitting items only as downstream consumers request them. If the Iterable is empty, the resulting Flux completes immediately after subscription. If the input is null, a NullPointerException is thrown. If the Iterable yields a null element, a NullPointerException will be signaled to the subscriber, since Reactor publishers do not allow null signals.

Use cases include converting in-memory collections into reactive streams for downstream processing. This enables applying Reactor operators such as map, filter, flatMap, and reduce within a reactive pipeline. It is commonly used to bridge traditional collections with reactive programming models, allowing seamless composition with other publishers and operators.

In summary, Flux.fromIterable provides a straightforward, backpressure-aware way to adapt an Iterable into a Reactor Flux, preserving iteration order, deferring work until subscription, and integrating with the broader reactive ecosystem.