如何从 Akka Streams Sink 中抛出的异常中恢复？

Question

如何从 Akka Streams 接收器中抛出的异常中恢复？

简单示例：

    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);

输出：

Sink: 1
Sink: 2
Sink: 3

如何处理异常并从源移至下一个元素？ （又名 5,6,7,8,9）

Answer 1

默认情况下，supervision strategy 在抛出异常时会停止流。要更改监督策略以删除导致异常的消息并继续处理下一条消息，请使用“恢复”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);

您还可以为不同类型的异常定义不同的监督策略：

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