Merge pull request #1640 from mdipirro/scala-672-stream-errors

SCALA-672 Add code for stream error handling

Author: lor6

build.sbt

@@ -338,6 +338,8 @@ lazy val scala_akka_3 = (project in file("scala-akka-3"))
     libraryDependencies ++= Seq(
       "com.typesafe.akka" %% "akka-stream" % AkkaVersion,
       "com.typesafe.akka" %% "akka-discovery" % AkkaVersion,
+      "org.slf4j" % "slf4j-api" % "2.0.16",
+      "org.slf4j" % "slf4j-simple" % "2.0.16",
       "com.typesafe.akka" %% "akka-stream-testkit" % AkkaVersion % Test,
       akkaActorTyped,
       akkaStreamDep,

scala-akka-3/src/main/scala/com/baeldung/scala/akka/stream/errors/Main.scala

@@ -0,0 +1,42 @@
+package com.baeldung.scala.akka.stream.errors
+
+import akka.actor.ActorSystem
+import akka.stream.RestartSettings
+import akka.stream.scaladsl.RestartSource
+
+import scala.concurrent.duration.DurationInt
+import scala.language.postfixOps
+import scala.util.{Failure, Success}
+
+object Main extends App {
+  implicit val system: ActorSystem = ActorSystem("baeldung")
+
+  private val backoffSettings = RestartSettings(
+    minBackoff = 3 seconds,
+    maxBackoff = 30 seconds,
+    randomFactor = 0.2
+  ).withMaxRestarts(3, 5.minutes)
+
+  RestartSource
+    .withBackoff(backoffSettings) { () => source }
+    .via(parse)
+    .via(compare)
+    .runWith(sink)
+    .andThen {
+      case Failure(exception) => println(exception)
+      case Success((correct, total)) =>
+        println(s"$correct/$total correct answers")
+    }(system.dispatcher)
+    .onComplete(_ => system.terminate())(system.dispatcher)
+
+  /*source
+    .via(parseWithLogging)
+    .via(compare)
+    .runWith(sink)
+    .andThen {
+      case Failure(exception) => println(exception)
+      case Success((correct, total)) =>
+        println(s"$correct/$total correct answers")
+    }(system.dispatcher)
+    .onComplete(_ => system.terminate())(system.dispatcher)*/
+}

scala-akka-3/src/main/scala/com/baeldung/scala/akka/stream/errors/package.scala

@@ -0,0 +1,53 @@
+package com.baeldung.scala.akka.stream
+
+import akka.NotUsed
+import akka.stream.Attributes
+import akka.stream.scaladsl.{Flow, Sink, Source}
+
+import scala.concurrent.Future
+
+package object errors {
+  val source: Source[String, NotUsed] = Source(
+    Seq("5,10", "15,15", "78,79", "12,12", "0,0", "456,456")
+  )
+
+  val parse: Flow[String, (Int, Int), NotUsed] =
+    Flow[String]
+      .map { pair =>
+        val parts = pair.split(",")
+        (parts(0).toInt, parts(1).toInt)
+      }
+
+  val parseWithRecover: Flow[String, Either[String, (Int, Int)], NotUsed] =
+    Flow[String]
+      .map { pair =>
+        val parts = pair.split(",")
+        Right((parts(0).toInt, parts(1).toInt))
+      }
+      .recover({ case e: ArrayIndexOutOfBoundsException =>
+        Left(e.getMessage)
+      })
+
+  val parseWithLogging: Flow[String, (Int, Int), NotUsed] =
+    Flow[String]
+      .map { pair =>
+        val parts = pair.split(",")
+        (parts(0).toInt, parts(1).toInt)
+      }
+      .log(name = "Baeldung stream")
+      .addAttributes(
+        Attributes.logLevels(
+          onElement = Attributes.LogLevels.Info
+        )
+      )
+
+  val compare: Flow[(Int, Int), Boolean, NotUsed] =
+    Flow[(Int, Int)]
+      .map { case (userAnswer, correctAnswer) => userAnswer == correctAnswer }
+
+  val sink: Sink[Boolean, Future[(Int, Int)]] = Sink.fold((0, 0)) {
+    case ((correctCount, total), wasCorrect) =>
+      if (wasCorrect) (correctCount + 1, total + 1)
+      else (correctCount, total + 1)
+  }
+}

scala-akka-3/src/test/scala/com/baeldung/scala/akka/stream/errors/ErrorRecoveryUnitTest.scala

@@ -0,0 +1,53 @@
+package com.baeldung.scala.akka.stream.errors
+
+import akka.actor.ActorSystem
+import akka.stream.{ActorAttributes, Supervision}
+import akka.stream.scaladsl.Keep
+import akka.stream.testkit.scaladsl.{TestSink, TestSource}
+import org.scalatest.concurrent.ScalaFutures.convertScalaFuture
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.matchers.should.Matchers
+
+class ErrorRecoveryUnitTest extends AnyFlatSpec with Matchers {
+  implicit val system: ActorSystem = ActorSystem("baeldung")
+
+  "The \"parseWithRecover\" flow" should "parse recover from a parsing error" in {
+    val (pub, sub) = TestSource[String]()
+      .via(parseWithRecover)
+      .toMat(TestSink[Either[String, (Int, Int)]]())(Keep.both)
+      .run()
+
+    pub.sendNext("1,1")
+    pub.sendNext("145146")
+    pub.sendComplete()
+
+    sub.requestNext(Right(1, 1))
+    sub.requestNext(Left("Index 1 out of bounds for length 1"))
+    sub.expectComplete()
+  }
+
+  "The \"Resume\" supervision strategy" should "ignore parsing errors" in {
+    val runnableGraph = TestSource[String]()
+      .via(parseWithRecover)
+      .toMat(TestSink[Either[String, (Int, Int)]]())(Keep.both)
+
+    val decider: Supervision.Decider = {
+      case _: ArrayIndexOutOfBoundsException => Supervision.Resume
+      case _                                 => Supervision.Stop
+    }
+
+    val graphWithResumeSupervision =
+      runnableGraph.withAttributes(ActorAttributes.supervisionStrategy(decider))
+
+    val (pub, sub) = graphWithResumeSupervision.run()
+
+    pub.sendNext("1,1")
+    pub.sendNext("145146")
+    pub.sendNext("1,2")
+    pub.sendComplete()
+
+    sub.requestNext(Right(1, 1))
+    sub.requestNext(Right(1, 2))
+    sub.expectComplete()
+  }
+}