README.md

Flink4s

Scala 2.13 and 3.x wrapper for Apache Flink. Scala is not a priority for the core project, and thus support for the latest versions of Scala is missing. This project attempts to leverage the Scala-free 1.15 release to provide a viable wrapper for Scala 2.13 and 3.x.

Usage

In your build.sbt, add

libraryDependencies ++= Seq(
  "com.ariskk" %% "flink4s" % "1.15.2"
)

Note: Major and minor versions follow Flink releases. Patches are independent.

Use it as you would use flink-streaming-scala. Most methods are identical

import com.ariskk.flink4s.StreamExecutionEnvironment

final case class Counter(id: String, count: Int)
object Counter:
  given typeInfo: TypeInformation[Counter] = TypeInformation.of(classOf[Counter])

val items = (1 to 1000).map(x => s"item-${x % 10}")

val stream = StreamExecutionEnvironment.fromCollection(items)
  .map(x => Counter(x, 1))
  .keyBy(_.id)
  .reduce((acc, v) => acc.copy(counter = acc.count + v.count))

Or if you want to get fancy:

import cats.Semigroup

given semigroup: Semigroup[Counter] with
  def combine(x: Counter, y: Counter) = Counter(x.id, x.value + y.value)

val stream = StreamExecutionEnvironment.fromCollection(items)
  .map(x => Counter(x, 1))
  .keyBy(_.id)
  .combine

Caveats

There is a number of features found in flink-streaming-scala that is (intentionally) missing:

• No automatic derivation of TypeInformation instances via macros. Compile times scale very poorly as codebase sizes increase. This means that some custom serializers Flink provides won't be used. For more context, check this.
• No closure cleaner. It is very hard to implement and generally imperfect. If all stream processing logic lives in objects, then there is no need for a closure cleaner in the first place.

Contributing

I would very much love contributions. The lowest hanging fruit would be opening a PR with methods from flink-streaming-scala that are currently missing. Ideally, this repo should move to its own org at some point.