类型为withValueSerde()的方法Materialized<>不适用

Question

我正在按键对流进行分组，并试图按分组键聚合值。我在跟踪流.开发人员.指南

我在withValueSerde上有个错误。上面写着：

The method withValueSerde(Serde<Object>) in the type Materialized<Object,Object,StateStore> is not applicable for the arguments (Serde<Long>)

代码：

KStream<String, String> inputStream = builder.stream("input_topic");
KStream<String, Integer> transformedStream = inputStream.map(
        (key, value) ->  KeyValue.pair(getKey(value), getValue(value)));

KGroupedStream<String, Integer> groupedStream = transformedStream.groupByKey();

KTable<String, Long> aggregatedStream = groupedStream.aggregate(() -> 0L,
        (aggKey, newValue, aggValue) -> aggValue + newValue,
        Materialized.as("aggregated-stream-store").withValueSerde(Serdes.Long()));

Answer 1

您需要指定泛型类型。Java不能自动推断它们(如果您查看错误消息，它只是表示表示未知类型的Materialized<Object,Object,StateStore> )：

Materialized.<String, Long, KeyValueStore<Bytes, byte[]>>as("aggregated-stream-store")
    .withValueSerde(Serdes.Long())