Kafka从给定主题流式处理KTable创建

Question

I'm doing a project and I'm stuck on the KTable.

I want to take records from a topic and put them in a KTable(store), so that I have 1 record for 1 key.

    static KafkaStreams streams;

    final Serde<Long> longSerde = Serdes.Long();
    final Serde<byte[]> byteSerde = Serdes.ByteArray();
    static String topicName;
    static String storeName;
    final StreamsBuilder builder = new StreamsBuilder();

    KStream<Long, byte[]> streamed = builder.stream(topicName, Consumed.with(longSerde, byteSerde));
    KTable<Long, byte[]> records = streamed.groupByKey().reduce(
            new Reducer<Long>() {
                @Override
                public Long apply(Long aggValue, Long newValue) {
                    return newValue;
                }
            }, 
            storeName);

This is the closest I got to the answer I think.

Answer 1

Your approach is correct, but you need to use the correct serdes.

In .reduce() function, value type should be byte[] .

 KStream<Long, byte[]> streamed = builder.stream(topicName, Consumed.with(longSerde, byteSerde));
 KTable<Long, byte[]> records = streamed.groupByKey().reduce(
            new Reducer<byte[]>() {
                @Override
                public byte[] apply(byte[] aggValue, byte[] newValue) {
                    return newValue;
                }
            }, 
            Materialized.as(storename).with(longSerde,byteSerde));