如何從 Akka Streams Sink 中拋出的異常中恢復？

Question

如何從 Akka Streams 的接收器中拋出的異常中恢復？

簡單示例：

    Source<Integer, NotUsed> integerSource = Source.from(Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9));

    integerSource.runWith(Sink.foreach(x -> {
      if (x == 4) {
        throw new Exception("Error Occurred");
      }
      System.out.println("Sink: " + x);
    }), system);

輸出：

Sink: 1
Sink: 2
Sink: 3

如何處理異常並從源移動到下一個元素？ （又名 5、6、7、8、9）

Answer 1

默認情況下，當拋出異常時， 監督策略會停止流。 要更改監督策略以丟棄導致異常的消息並繼續處理下一條消息，請使用“恢復”策略。 例如：

final Function<Throwable, Supervision.Directive> decider =
  exc -> {
    return Supervision.resume();
  };

final Sink<Integer, CompletionStage<Done>> printSink =
  Sink.foreach(x -> {
    if (x == 4) {
      throw new Exception("Error Occurred");
    }
    System.out.println("Sink: " + x);
  });

final RunnableGraph<CompletionStage<Done>> runnableGraph =
  integerSource.toMat(printSink, Keep.right());

final RunnableGraph<CompletionStage<Done>> withResumingSupervision =
  runnableGraph.withAttributes(ActorAttributes.withSupervisionStrategy(decider));

final CompletionStage<Done> result = withResumingSupervision.run(system);

您還可以為不同類型的異常定義不同的監督策略：

final Function<Throwable, Supervision.Directive> decider =
  exc -> {
    if (exc instanceof MySpecificException) return Supervision.resume();
    else return Supervision.stop();
  };