AKKA Streams

Experimenting with the AKKA Streams Library

Basic Elements of Akka Stream

Streams always start flowing from a Source[Out,M1] then can continue through Flow[In,Out,M2] elements or more advanced graph elements to finally be consumed by a Sink[In,M3]

Components can be reused typically we are defining blueprints for what we want to run then running them.

Sources: Emit a stream (Publishers)
Sinks: Receive a stream (Subscribers)
Flows: Receive a stream then emit a stream. Usually performing a transformation on stream items
Throttle: Controls the speed at which the stream flows. Will assert back pressure upstream if necessary

Akka streams always propagate back pressure from Sinks to Sources.

More Elements of Akka Stream

Junctions: Are used to form 'fan-in' or 'fan-out' structures. These structures either split a source stream or combine multiple streams into 1
- Broadcast: Emits elements from it's input ports to all of it's output ports
Buffers: Buffering must be handled explicitly

Materialized Values

A blueprint is defined for the stream using Source, Sink, Flow etc their type signatures also tell us what type they will be once materialized. Keep.right and Keep.left are used to specify that we should only care about the materialised type appended to the right or left. e.g

def lineSink(filename: String): Sink[String, Future[IOResult]] =
    Flow[String]
      .map(s ⇒ ByteString(s + "\n"))
      .toMat(fileSink(filename))(Keep.right)

runWith() is a convenience method that automatically ignores the materialized value of any other stages except those appended by the runWith()

Guides I'm reading

Questions for next time