Question

我正在尝试从Kafka Java中的KStream创建“差异”流。

我有一个输入流，其中的值是一组Doubles V0…Vn。输出流应计算V0-0，V1-V0，V2-V1…Vn -Vn-1之间的差。

我的第一个想法是做这样的事情：

    KStream<String, Double> stream = builder.stream(TOPIC)

    KTable<String, Double> difference = stream.groupByKey().reduce(
            (oldValue, newValue) -> {
              return newValue - oldValue
            }
    ).toStream()

假设我有一个具有以下值的KStream输入：

Key  -> Value
"A1" -> 2 
"B2" -> 4
"A1" -> 6
"A1" -> 10
"B2" -> 13 
"A1" -> 7

我想使用以下值创建一个新的Stream输出：

Key  -> Value
"A1" ->  2  (2-0  =  2) 
"B2" ->  4  (4-0  =  4)
"A1" ->  4  (6-2  =  4)
"A1" ->  4  (10-6 =  4)
"B2" ->  9  (13-4 =  9)
"A1" -> -3  (7-10 = -3)

Answer 1

您可以使用

之类的东西

        stream.groupByKey().aggregate(Diff::new, new Aggregator<String, Double, Diff>() {

        @Override
        public Diff apply(String key, Double newValue, Diff aggregate) {
            Double difference = newValue - aggregate.getLastValue();
            aggregate.setDifference(difference);
            aggregate.setLastValue(newValue);
            return aggregate;
        }
        }).mapValues(new ValueMapper<Diff, Double>() {

        @Override
        public Double apply(Diff value) {
            return value.getDifference();
        }

    }).toStream().to("diff");

其中

public class Diff {

  private Double lastValue = 0d;

  private Double difference = 0d;
  //getters and setters
  // ...
}

是否热衷于使用Java中的Kafka Streams创建差异流？

1 个答案: