Flow.lazyCompletionStageFlow
Defers creation and materialization of a Flow
until there is a first element.
Description
When the first element comes from upstream the actual CompletionStage<Flow>
is created and when that completes it is materialized and inserted in the stream. The internal Flow
will not be created if there are no elements on completion or failure of up or downstream.
The materialized value of the Flow
will be the materialized value of the created internal flow if it is materialized and failed with a akka.stream.NeverMaterializedException
if the stream fails or completes without the flow being materialized.
See also lazyFlow.
Can be combined with prefixAndTail(1)
to base the flow construction on the initial element triggering creation. See lazyFlow for sample.
Reactive Streams semantics
emits when the internal flow is successfully created and it emits
backpressures when the internal flow is successfully created and it backpressures
completes when upstream completes and all elements have been emitted from the internal flow
completes when upstream completes and all futures have been completed and all elements have been emitted