Package akka.stream.javadsl

Class Source$

  • public class Source$
extends java.lang.Object
    Java API

    • Field Detail

      • MODULE$

        public static final Source$ MODULE$
        Static reference to the singleton instance of this Scala object.

    • Constructor Detail

      • Source$

        public Source$()

    • Method Detail

      • empty

        public <O> Source<O,​NotUsed> empty()
        Create a Source with no elements, i.e. an empty stream that is completed immediately for every connected Sink.

      • empty

        public <T> Source<T,​NotUsed> empty​(java.lang.Class<T> clazz)
        Create a Source with no elements. The result is the same as calling Source.empty()

      • maybe

        public <T> Source<T,​java.util.concurrent.CompletableFuture<java.util.Optional<T>>> maybe()
        Create a Source which materializes a CompletableFuture which controls what element will be emitted by the Source. If the materialized promise is completed with a filled Optional, that value will be produced downstream, followed by completion. If the materialized promise is completed with an empty Optional, no value will be produced downstream and completion will be signalled immediately. If the materialized promise is completed with a failure, then the source will fail with that error. If the downstream of this source cancels or fails before the promise has been completed, then the promise will be completed with an empty Optional.

      • fromPublisher

        public <O> Source<O,​NotUsed> fromPublisher​(org.reactivestreams.Publisher<O> publisher)
        Helper to create Source from Publisher.

        Construct a transformation starting with given publisher. The transformation steps are executed by a series of Processor instances that mediate the flow of elements downstream and the propagation of back-pressure upstream.

      • fromIterator

        public <O> Source<O,​NotUsed> fromIterator​(Creator<java.util.Iterator<O>> f)
        Helper to create a Source from an Iterator. Example usage: 

        
 List<Integer> data = new ArrayList<Integer>();
 data.add(1);
 data.add(2);
 data.add(3);
 Source.from(() -> data.iterator());

        Start a new Source from the given Iterator. The produced stream of elements will continue until the iterator runs empty or fails during evaluation of the next() method. Elements are pulled out of the iterator in accordance with the demand coming from the downstream transformation steps.

      • fromJavaStream

        public <O,​S extends java.util.stream.BaseStream<O,​S>> Source<O,​NotUsed> fromJavaStream​(Creator<java.util.stream.BaseStream<O,​S>> stream)
        Creates a source that wraps a Java 8 Stream. Source uses a stream iterator to get all its elements and send them downstream on demand.

        You can use Source.async to create asynchronous boundaries between synchronous java stream and the rest of flow.

      • cycle

        public <O> Source<O,​NotUsed> cycle​(Creator<java.util.Iterator<O>> f)
        Helper to create a 'cycled' Source that will continually produce elements in the order they are provided.

        Example usage: 

        
 Source.cycle(() -> Arrays.asList(1, 2, 3).iterator());

        The function f is invoked to obtain an iterator and elements are emitted into the stream as provided by that iterator. If the iterator is finite, the function f invoked again, as necessary, when the elements from the previous iteration are exhausted. If every call to function f returns an iterator that produces the same elements in the same order, then the Source will effectively be cyclic. However, f is not required to behave that way, in which case the Source will not be cyclic.

        The Source fails if f returns an empty iterator.

      • from

        public <O> Source<O,​NotUsed> from​(java.lang.Iterable<O> iterable)
        Helper to create Source from Iterable. Example usage: 
        
 List<Integer> data = new ArrayList<Integer>();
 data.add(1);
 data.add(2);
 data.add(3);
 Source.from(data);

        Starts a new Source from the given Iterable. This is like starting from an Iterator, but every Subscriber directly attached to the Publisher of this stream will see an individual flow of elements (always starting from the beginning) regardless of when they subscribed.

        Make sure that the Iterable is immutable or at least not modified after being used as a Source. Otherwise the stream may fail with ConcurrentModificationException or other more subtle errors may occur.

      • range

        public Source<java.lang.Integer,​NotUsed> range​(int start,
                                                     int end)
        Creates Source that represents integer values in range ''[start;end]'', step equals to 1. It allows to create Source out of range as simply as on Scala Source(1 to N)

        Uses {@link scala.collection.immutable.Range.inclusive(Int, Int)} internally

      • range

        public Source<java.lang.Integer,​NotUsed> range​(int start,
                                                     int end,
                                                     int step)
        Creates Source that represents integer values in range ''[start;end]'', with the given step. It allows to create Source out of range as simply as on Scala Source(1 to N)

        Uses {@link scala.collection.immutable.Range.inclusive(Int, Int, Int)} internally

      • fromFuture

        public <O> Source<O,​NotUsed> fromFuture​(scala.concurrent.Future<O> future)
        Deprecated.
        Use 'Source.future' instead. Since 2.6.0.
        Start a new Source from the given Future. The stream will consist of one element when the Future is completed with a successful value, which may happen before or after materializing the Flow. The stream terminates with a failure if the Future is completed with a failure.

      • fromCompletionStage

        public <O> Source<O,​NotUsed> fromCompletionStage​(java.util.concurrent.CompletionStage<O> future)
        Deprecated.
        Use 'Source.completionStage' instead. Since 2.6.0.
        Starts a new Source from the given CompletionStage. The stream will consist of one element when the CompletionStage is completed with a successful value, which may happen before or after materializing the Flow. The stream terminates with a failure if the CompletionStage is completed with a failure.

      • fromFutureSource

        public <T,​M> Source<T,​scala.concurrent.Future<M>> fromFutureSource​(scala.concurrent.Future<? extends Graph<SourceShape<T>,​M>> future)
        Deprecated.
        Use 'Source.futureSource' (potentially together with `Source.fromGraph`) instead. Since 2.6.0.
        Streams the elements of the given future source once it successfully completes. If the Future fails the stream is failed with the exception from the future. If downstream cancels before the stream completes the materialized Future will be failed with a StreamDetachedException.

      • fromSourceCompletionStage

        public <T,​M> Source<T,​java.util.concurrent.CompletionStage<M>> fromSourceCompletionStage​(java.util.concurrent.CompletionStage<? extends Graph<SourceShape<T>,​M>> completion)
        Deprecated.
        Use 'Source.completionStageSource' (potentially together with `Source.fromGraph`) instead. Since 2.6.0.
        Streams the elements of an asynchronous source once its given CompletionStage completes. If the CompletionStage fails the stream is failed with the exception from the future. If downstream cancels before the stream completes the materialized CompletionStage will be failed with a StreamDetachedException

      • tick

        public <O> Source<O,​Cancellable> tick​(java.time.Duration initialDelay,
                                            java.time.Duration interval,
                                            O tick)
        Elements are emitted periodically with the specified interval. The tick element will be delivered to downstream consumers that has requested any elements. If a consumer has not requested any elements at the point in time when the tick element is produced it will not receive that tick element later. It will receive new tick elements as soon as it has requested more elements.

      • single

        public <T> Source<T,​NotUsed> single​(T element)
        Create a Source with one element. Every connected Sink of this stream will see an individual stream consisting of one element.

      • repeat

        public <T> Source<T,​NotUsed> repeat​(T element)
        Create a Source that will continually emit the given element.

      • unfold

        public <S,​E> Source<E,​NotUsed> unfold​(S s,
                                                  Function<S,​java.util.Optional<Pair<S,​E>>> f)
        Create a Source that will unfold a value of type S into a pair of the next state S and output elements of type E.

      • failed

        public <T> Source<T,​NotUsed> failed​(java.lang.Throwable cause)
        Create a Source that immediately ends the stream with the cause failure to every connected Sink.

      • lazily

        public <T,​M> Source<T,​java.util.concurrent.CompletionStage<M>> lazily​(Creator<Source<T,​M>> create)
        Deprecated.
        Use 'Source.lazySource' instead. Since 2.6.0.
        Creates a Source that is not materialized until there is downstream demand, when the source gets materialized the materialized future is completed with its value, if downstream cancels or fails without any demand the create factory is never called and the materialized CompletionStage is failed.

      • lazilyAsync

        public <T> Source<T,​scala.concurrent.Future<NotUsed>> lazilyAsync​(Creator<java.util.concurrent.CompletionStage<T>> create)
        Deprecated.
        Use 'Source.lazyCompletionStage' instead. Since 2.6.0.
        Creates a Source from supplied future factory that is not called until downstream demand. When source gets materialized the materialized future is completed with the value from the factory. If downstream cancels or fails without any demand the create factory is never called and the materialized Future is failed.

        See Also:
        Source.lazily

      • future

        public <T> Source<T,​NotUsed> future​(scala.concurrent.Future<T> futureElement)
        Emits a single value when the given Scala Future is successfully completed and then completes the stream. The stream fails if the Future is completed with a failure.

        Here for Java interoperability, the normal use from Java should be Source.completionStage

      • never

        public <T> Source<T,​NotUsed> never()
        Never emits any elements, never completes and never fails. This stream could be useful in tests.

      • completionStage

        public <T> Source<T,​NotUsed> completionStage​(java.util.concurrent.CompletionStage<T> completionStage)
        Emits a single value when the given CompletionStage is successfully completed and then completes the stream. If the CompletionStage is completed with a failure the stream is failed.

      • completionStageSource

        public <T,​M> Source<T,​java.util.concurrent.CompletionStage<M>> completionStageSource​(java.util.concurrent.CompletionStage<Source<T,​M>> completionStageSource)
        Turn a CompletionStage[Source] into a source that will emit the values of the source when the future completes successfully. If the CompletionStage is completed with a failure the stream is failed.

      • lazySingle

        public <T> Source<T,​NotUsed> lazySingle​(Creator<T> create)
        Defers invoking the create function to create a single element until there is downstream demand.

        If the create function fails when invoked the stream is failed.

        Note that asynchronous boundaries (and other operators) in the stream may do pre-fetching which counter acts the laziness and will trigger the factory immediately.

        The materialized future Done value is completed when the create function has successfully been invoked, if the function throws the future materialized value is failed with that exception. If downstream cancels or fails before the function is invoked the materialized value is failed with a NeverMaterializedException

      • lazyCompletionStage

        public <T> Source<T,​NotUsed> lazyCompletionStage​(Creator<java.util.concurrent.CompletionStage<T>> create)
        Defers invoking the create function to create a future element until there is downstream demand.

        The returned future element will be emitted downstream when it completes, or fail the stream if the future is failed or the create function itself fails.

        Note that asynchronous boundaries (and other operators) in the stream may do pre-fetching which counter acts the laziness and will trigger the factory immediately.

        The materialized future Done value is completed when the create function has successfully been invoked and the future completes, if the function throws or the future fails the future materialized value is failed with that exception. If downstream cancels or fails before the function is invoked the materialized value is failed with a NeverMaterializedException

      • lazySource

        public <T,​M> Source<T,​java.util.concurrent.CompletionStage<M>> lazySource​(Creator<Source<T,​M>> create)
        Defers invoking the create function to create a future source until there is downstream demand.

        The returned source will emit downstream and behave just like it was the outer source. Downstream completes when the created source completes and fails when the created source fails.

        Note that asynchronous boundaries (and other operators) in the stream may do pre-fetching which counter acts the laziness and will trigger the factory immediately.

        The materialized future value is completed with the materialized value of the created source when it has been materialized. If the function throws or the source materialization fails the future materialized value is failed with the thrown exception.

        If downstream cancels or fails before the function is invoked the materialized value is failed with a NeverMaterializedException

      • lazyCompletionStageSource

        public <T,​M> Source<T,​java.util.concurrent.CompletionStage<M>> lazyCompletionStageSource​(Creator<java.util.concurrent.CompletionStage<Source<T,​M>>> create)
        Defers invoking the create function to create a future source until there is downstream demand.

        The returned future source will emit downstream and behave just like it was the outer source when the CompletionStage completes successfully. Downstream completes when the created source completes and fails when the created source fails. If the CompletionStage or the create function fails the stream is failed.

        Note that asynchronous boundaries (and other operators) in the stream may do pre-fetching which counter acts the laziness and triggers the factory immediately.

        The materialized CompletionStage value is completed with the materialized value of the created source when it has been materialized. If the function throws or the source materialization fails the future materialized value is failed with the thrown exception.

        If downstream cancels or fails before the function is invoked the materialized value is failed with a NeverMaterializedException

      • asSubscriber

        public <T> Source<T,​org.reactivestreams.Subscriber<T>> asSubscriber()
        Creates a Source that is materialized as a Subscriber

      • actorRef

        public <T> Source<T,​ActorRef> actorRef​(Function<java.lang.Object,​java.util.Optional<CompletionStrategy>> completionMatcher,
                                             Function<java.lang.Object,​java.util.Optional<java.lang.Throwable>> failureMatcher,
                                             int bufferSize,
                                             OverflowStrategy overflowStrategy)
        Creates a Source that is materialized as an ActorRef. Messages sent to this actor will be emitted to the stream if there is demand from downstream, otherwise they will be buffered until request for demand is received.

        Depending on the defined OverflowStrategy it might drop elements if there is no space available in the buffer.

        The strategy akka.stream.OverflowStrategy.backpressure is not supported, and an IllegalArgument("Backpressure overflowStrategy not supported") will be thrown if it is passed as argument.

        The buffer can be disabled by using bufferSize of 0 and then received messages are dropped if there is no demand from downstream. When bufferSize is 0 the overflowStrategy does not matter.

        The stream can be completed successfully by sending the actor reference a message that is matched by completionMatcher in which case already buffered elements will be signaled before signaling completion.

        The stream can be completed with failure by sending a message that is matched by failureMatcher. The extracted Throwable will be used to fail the stream. In case the Actor is still draining its internal buffer (after having received a message matched by completionMatcher) before signaling completion and it receives a message matched by failureMatcher, the failure will be signaled downstream immediately (instead of the completion signal).

        Note that terminating the actor without first completing it, either with a success or a failure, will prevent the actor triggering downstream completion and the stream will continue to run even though the source actor is dead. Therefore you should **not** attempt to manually terminate the actor such as with a PoisonPill.

        The actor will be stopped when the stream is completed, failed or canceled from downstream, i.e. you can watch it to get notified when that happens.

        See also akka.stream.scaladsl.Source.queue.

        Parameters:
        completionMatcher - catches the completion message to end the stream
        failureMatcher - catches the failure message to fail the stream
        bufferSize - The size of the buffer in element count
        overflowStrategy - Strategy that is used when incoming elements cannot fit inside the buffer

      • actorRef

        public <T> Source<T,​ActorRef> actorRef​(int bufferSize,
                                             OverflowStrategy overflowStrategy)
        Deprecated.
        Use variant accepting completion and failure matchers. Since 2.6.0.
        Creates a Source that is materialized as an ActorRef. Messages sent to this actor will be emitted to the stream if there is demand from downstream, otherwise they will be buffered until request for demand is received.

        Depending on the defined OverflowStrategy it might drop elements if there is no space available in the buffer.

        The strategy akka.stream.OverflowStrategy.backpressure is not supported, and an IllegalArgument("Backpressure overflowStrategy not supported") will be thrown if it is passed as argument.

        The buffer can be disabled by using bufferSize of 0 and then received messages are dropped if there is no demand from downstream. When bufferSize is 0 the overflowStrategy does not matter.

        The stream can be completed successfully by sending the actor reference a Status.Success (whose content will be ignored) in which case already buffered elements will be signaled before signaling completion.

        The stream can be completed successfully by sending the actor reference a Status.Success. If the content is akka.stream.CompletionStrategy.immediately the completion will be signaled immediately, otherwise if the content is akka.stream.CompletionStrategy.draining (or anything else) already buffered elements will be signaled before signaling completion. Sending PoisonPill will signal completion immediately but this behavior is deprecated and scheduled to be removed.

        The stream can be completed with failure by sending a Status.Failure to the actor reference. In case the Actor is still draining its internal buffer (after having received a Status.Success) before signaling completion and it receives a Status.Failure, the failure will be signaled downstream immediately (instead of the completion signal).

        Note that terminating the actor without first completing it, either with a success or a failure, will prevent the actor triggering downstream completion and the stream will continue to run even though the source actor is dead. Therefore you should **not** attempt to manually terminate the actor such as with a PoisonPill.

        The actor will be stopped when the stream is completed, failed or canceled from downstream, i.e. you can watch it to get notified when that happens.

        See also akka.stream.javadsl.Source.queue.

        Parameters:
        bufferSize - The size of the buffer in element count
        overflowStrategy - Strategy that is used when incoming elements cannot fit inside the buffer

      • actorRefWithBackpressure

        public <T> Source<T,​ActorRef> actorRefWithBackpressure​(java.lang.Object ackMessage,
                                                             Function<java.lang.Object,​java.util.Optional<CompletionStrategy>> completionMatcher,
                                                             Function<java.lang.Object,​java.util.Optional<java.lang.Throwable>> failureMatcher)
        Creates a Source that is materialized as an ActorRef. Messages sent to this actor will be emitted to the stream if there is demand from downstream, and a new message will only be accepted after the previous messages has been consumed and acknowledged back. The stream will complete with failure if a message is sent before the acknowledgement has been replied back.

        The stream can be completed with failure by sending a message that is matched by failureMatcher. The extracted Throwable will be used to fail the stream. In case the Actor is still draining its internal buffer (after having received a message matched by completionMatcher) before signaling completion and it receives a message matched by failureMatcher, the failure will be signaled downstream immediately (instead of the completion signal).

        The actor will be stopped when the stream is completed, failed or canceled from downstream, i.e. you can watch it to get notified when that happens.

      • actorRefWithAck

        public <T> Source<T,​ActorRef> actorRefWithAck​(java.lang.Object ackMessage,
                                                    Function<java.lang.Object,​java.util.Optional<CompletionStrategy>> completionMatcher,
                                                    Function<java.lang.Object,​java.util.Optional<java.lang.Throwable>> failureMatcher)
        Deprecated.
        Use actorRefWithBackpressure instead
        Creates a Source that is materialized as an ActorRef. Messages sent to this actor will be emitted to the stream if there is demand from downstream, and a new message will only be accepted after the previous messages has been consumed and acknowledged back. The stream will complete with failure if a message is sent before the acknowledgement has been replied back.

        The stream can be completed with failure by sending a message that is matched by failureMatcher. The extracted Throwable will be used to fail the stream. In case the Actor is still draining its internal buffer (after having received a message matched by completionMatcher) before signaling completion and it receives a message matched by failureMatcher, the failure will be signaled downstream immediately (instead of the completion signal).

        The actor will be stopped when the stream is completed, failed or canceled from downstream, i.e. you can watch it to get notified when that happens.

      • actorRefWithAck

        public <T> Source<T,​ActorRef> actorRefWithAck​(java.lang.Object ackMessage)
        Deprecated.
        Use actorRefWithBackpressure accepting completion and failure matchers. Since 2.6.0.
        Creates a Source that is materialized as an ActorRef. Messages sent to this actor will be emitted to the stream if there is demand from downstream, and a new message will only be accepted after the previous messages has been consumed and acknowledged back. The stream will complete with failure if a message is sent before the acknowledgement has been replied back.

        The stream can be completed successfully by sending the actor reference a Status.Success. If the content is akka.stream.CompletionStrategy.immediately the completion will be signaled immediately, otherwise if the content is akka.stream.CompletionStrategy.draining (or anything else) already buffered element will be signaled before signaling completion.

        The stream can be completed with failure by sending a Status.Failure to the actor reference. In case the Actor is still draining its internal buffer (after having received a Status.Success) before signaling completion and it receives a Status.Failure, the failure will be signaled downstream immediately (instead of the completion signal).

        The actor will be stopped when the stream is completed, failed or canceled from downstream, i.e. you can watch it to get notified when that happens.

      • fromGraph

        public <T,​M> Source<T,​M> fromGraph​(Graph<SourceShape<T>,​M> g)
        A graph with the shape of a source logically is a source, this method makes it so also in type.

      • fromMaterializer

        public <T,​M> Source<T,​java.util.concurrent.CompletionStage<M>> fromMaterializer​(java.util.function.BiFunction<Materializer,​Attributes,​Source<T,​M>> factory)
        Defers the creation of a Source until materialization. The factory function exposes Materializer which is going to be used during materialization and Attributes of the Source returned by this method.

      • setup

        public <T,​M> Source<T,​java.util.concurrent.CompletionStage<M>> setup​(java.util.function.BiFunction<ActorMaterializer,​Attributes,​Source<T,​M>> factory)
        Deprecated.
        Use 'fromMaterializer' instead. Since 2.6.0.
        Defers the creation of a Source until materialization. The factory function exposes ActorMaterializer which is going to be used during materialization and Attributes of the Source returned by this method.

      • combineMat

        public <T,​U,​M1,​M2,​M> Source<U,​M> combineMat​(Source<T,​M1> first,
                                                                          Source<T,​M2> second,
                                                                          Function<java.lang.Integer,​? extends Graph<UniformFanInShape<T,​U>,​NotUsed>> fanInStrategy,
                                                                          Function2<M1,​M2,​M> matF)
        Combines two sources with fan-in strategy like Merge or Concat and returns Source with a materialized value.

      • zipN

        public <T> Source<java.util.List<T>,​NotUsed> zipN​(java.util.List<Source<T,​?>> sources)
        Combine the elements of multiple streams into a stream of lists.

      • zipWithN

        public <T,​O> Source<O,​NotUsed> zipWithN​(Function<java.util.List<T>,​O> zipper,
                                                    java.util.List<Source<T,​?>> sources)

      • queue

        public <T> Source<T,​BoundedSourceQueue<T>> queue​(int bufferSize)
        Creates a Source that is materialized as an BoundedSourceQueue. You can push elements to the queue and they will be emitted to the stream if there is demand from downstream, otherwise they will be buffered until request for demand is received. The buffer size is passed in as a parameter. Elements in the buffer will be discarded if downstream is terminated.

        Pushed elements may be dropped if there is no space available in the buffer. Elements will also be dropped if the queue is failed through the materialized BoundedQueueSource or the Source is cancelled by the downstream. An element that was reported to be enqueued is not guaranteed to be processed by the rest of the stream. If the queue is failed by calling BoundedQueueSource.fail or the downstream cancels the stream, elements in the buffer are discarded.

        Acknowledgement of pushed elements is immediate. akka.stream.BoundedSourceQueue.offer returns QueueOfferResult which is implemented as:

        QueueOfferResult.enqueued() element was added to buffer, but may still be discarded later when the queue is failed or cancelled QueueOfferResult.dropped() element was dropped QueueOfferResult.QueueClosed the queue was completed with akka.stream.BoundedSourceQueue.complete QueueOfferResult.Failure the queue was failed with akka.stream.BoundedSourceQueue.fail or if the stream failed

        Parameters:
        bufferSize - size of the buffer in number of elements

      • queue

        public <T> Source<T,​SourceQueueWithComplete<T>> queue​(int bufferSize,
                                                            OverflowStrategy overflowStrategy)
        Creates a Source that is materialized as an SourceQueueWithComplete. You can push elements to the queue and they will be emitted to the stream if there is demand from downstream, otherwise they will be buffered until request for demand is received. Elements in the buffer will be discarded if downstream is terminated.

        Depending on the defined OverflowStrategy it might drop elements if there is no space available in the buffer.

        Acknowledgement mechanism is available. akka.stream.javadsl.SourceQueueWithComplete.offer returns CompletionStage which completes with QueueOfferResult.enqueued() if element was added to buffer or sent downstream. It completes with QueueOfferResult.dropped() if element was dropped. Can also complete with QueueOfferResult.Failure - when stream failed or QueueOfferResult.QueueClosed when downstream is completed.

        The strategy akka.stream.OverflowStrategy.backpressure will not complete last offer():CompletionStage call when buffer is full.

        Instead of using the strategy akka.stream.OverflowStrategy.dropNew it's recommended to use Source.queue(bufferSize) instead which returns a QueueOfferResult synchronously.

        You can watch accessibility of stream with akka.stream.javadsl.SourceQueueWithComplete.watchCompletion. It returns a future that completes with success when this operator is completed or fails when stream is failed.

        The buffer can be disabled by using bufferSize of 0 and then received message will wait for downstream demand unless there is another message waiting for downstream demand, in that case offer result will be completed according to the overflow strategy.

        The materialized SourceQueue may only be used from a single producer.

        Parameters:
        bufferSize - size of buffer in element count
        overflowStrategy - Strategy that is used when incoming elements cannot fit inside the buffer

      • queue

        public <T> Source<T,​SourceQueueWithComplete<T>> queue​(int bufferSize,
                                                            OverflowStrategy overflowStrategy,
                                                            int maxConcurrentOffers)
        Creates a Source that is materialized as an SourceQueueWithComplete. You can push elements to the queue and they will be emitted to the stream if there is demand from downstream, otherwise they will be buffered until request for demand is received. Elements in the buffer will be discarded if downstream is terminated.

        Depending on the defined OverflowStrategy it might drop elements if there is no space available in the buffer.

        Acknowledgement mechanism is available. akka.stream.javadsl.SourceQueueWithComplete.offer returns CompletionStage which completes with QueueOfferResult.enqueued() if element was added to buffer or sent downstream. It completes with QueueOfferResult.dropped() if element was dropped. Can also complete with QueueOfferResult.Failure - when stream failed or QueueOfferResult.QueueClosed when downstream is completed.

        The strategy akka.stream.OverflowStrategy.backpressure will not complete maxConcurrentOffers number of offer():CompletionStage call when buffer is full.

        Instead of using the strategy akka.stream.OverflowStrategy.dropNew it's recommended to use Source.queue(bufferSize) instead which returns a QueueOfferResult synchronously.

        You can watch accessibility of stream with akka.stream.javadsl.SourceQueueWithComplete.watchCompletion. It returns a future that completes with success when this operator is completed or fails when stream is failed.

        The buffer can be disabled by using bufferSize of 0 and then received message will wait for downstream demand unless there is another message waiting for downstream demand, in that case offer result will be completed according to the overflow strategy.

        The materialized SourceQueue may be used by up to maxConcurrentOffers concurrent producers.

        Parameters:
        bufferSize - size of buffer in element count
        overflowStrategy - Strategy that is used when incoming elements cannot fit inside the buffer
        maxConcurrentOffers - maximum number of pending offers when buffer is full, should be greater than 0, not applicable when OverflowStrategy.dropNew is used

      • unfoldResource

        public <T,​S> Source<T,​NotUsed> unfoldResource​(Creator<S> create,
                                                          Function<S,​java.util.Optional<T>> read,
                                                          Procedure<S> close)
        Start a new Source from some resource which can be opened, read and closed. Interaction with resource happens in a blocking way.

        Example: 

        
 Source.unfoldResource(
   () -> new BufferedReader(new FileReader("...")),
   reader -> reader.readLine(),
   reader -> reader.close())

        You can use the supervision strategy to handle exceptions for read function. All exceptions thrown by create or close will fail the stream.

        Restart supervision strategy will close and create blocking IO again. Default strategy is Stop which means that stream will be terminated on error in read function by default.

        You can configure the default dispatcher for this Source by changing the akka.stream.materializer.blocking-io-dispatcher or set it for a given Source by using ActorAttributes.

        Adheres to the ActorAttributes.SupervisionStrategy attribute.

        Parameters:
        create - - function that is called on stream start and creates/opens resource.
        read - - function that reads data from opened resource. It is called each time backpressure signal is received. Stream calls close and completes when read returns an empty Optional.
        close - - function that closes resource

      • unfoldResourceAsync

        public <T,​S> Source<T,​NotUsed> unfoldResourceAsync​(Creator<java.util.concurrent.CompletionStage<S>> create,
                                                               Function<S,​java.util.concurrent.CompletionStage<java.util.Optional<T>>> read,
                                                               Function<S,​java.util.concurrent.CompletionStage<Done>> close)
        Start a new Source from some resource which can be opened, read and closed. It's similar to unfoldResource but takes functions that return CompletionStage instead of plain values.

        You can use the supervision strategy to handle exceptions for read function or failures of produced Futures. All exceptions thrown by create or close as well as fails of returned futures will fail the stream.

        Restart supervision strategy will close and create resource. Default strategy is Stop which means that stream will be terminated on error in read function (or future) by default.

        You can configure the default dispatcher for this Source by changing the akka.stream.materializer.blocking-io-dispatcher or set it for a given Source by using ActorAttributes.

        Adheres to the ActorAttributes.SupervisionStrategy attribute.

        Parameters:
        create - - function that is called on stream start and creates/opens resource.
        read - - function that reads data from opened resource. It is called each time backpressure signal is received. Stream calls close and completes when CompletionStage from read function returns an empty Optional.
        close - - function that closes resource

      • upcast

        public <SuperOut,​Out extends SuperOut,​Mat> Source<SuperOut,​Mat> upcast​(Source<Out,​Mat> source)
        Upcast a stream of elements to a stream of supertypes of that element. Useful in combination with fan-in operators where you do not want to pay the cost of casting each element in a map.

        Example: 

        
 Source<Apple, NotUsed> apples = Source.single(new Apple());
 Source<Orange, NotUsed> oranges = Source.single(new Orange());
 Source<Fruit, NotUsed> appleFruits = Source.upcast(apples);
 Source<Fruit, NotUsed> orangeFruits = Source.upcast(oranges);

 Source<Fruit, NotUsed> fruits = appleFruits.merge(orangeFruits);

        Returns:
        A source with the supertype as elements

      • mergePrioritizedN

        public <T> Source<T,​NotUsed> mergePrioritizedN​(java.util.List<Pair<Source<T,​?>,​java.lang.Integer>> sourcesAndPriorities,
                                                     boolean eagerComplete)
        Merge multiple Sources. Prefer the sources depending on the 'priority' parameters. The provided sources and priorities must have the same size and order.

        '''emits''' when one of the inputs has an element available, preferring inputs based on the 'priority' parameters if both have elements available

        '''backpressures''' when downstream backpressures

        '''completes''' when both upstreams complete (This behavior is changeable to completing when any upstream completes by setting eagerComplete=true.)

        '''Cancels when''' downstream cancels