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OrElse stage for fallback when no elements emitted #21024

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Johan Andrén 2016-08-30 13:35:59 +02:00 • committed by GitHub
parent fbfc8b4c58
commit 012919fdb3
12 changed files with 465 additions and 7 deletions
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25
akka-stream/src/main/scala/akka/stream/javadsl/SubSource.scala
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@ -980,6 +980,31 @@ class SubSource[+Out, +Mat](delegate: scaladsl.SubFlow[Out, Mat, scaladsl.Source
def prepend[T >: Out, M](that: Graph[SourceShape[T], M]): SubSource[T, Mat] =
new SubSource(delegate.prepend(that))
/**
* Provides a secondary source that will be consumed if this source completes without any
* elements passing by. As soon as the first element comes through this stream, the alternative
* will be cancelled.
*
* Note that this Flow will be materialized together with the [[Source]] and just kept
* from producing elements by asserting back-pressure until its time comes or it gets
* cancelled.
*
* On errors the stage is failed regardless of source of the error.
*
* '''Emits when''' element is available from first stream or first stream closed without emitting any elements and an element
* is available from the second stream
*
* '''Backpressures when''' downstream backpressures
*
* '''Completes when''' the primary stream completes after emitting at least one element, when the primary stream completes
* without emitting and the secondary stream already has completed or when the secondary stream completes
*
* '''Cancels when''' downstream cancels and additionally the alternative is cancelled as soon as an element passes
* by from this stream.
*/
def orElse[T >: Out, M](secondary: Graph[SourceShape[T], M]): javadsl.SubSource[T, Mat] =
new SubSource(delegate.orElse(secondary))
/**
* Attaches the given [[Sink]] to this [[Flow]], meaning that elements that passes
* through will also be sent to the [[Sink]].