Kafka Streams物化商店构建错误

Question

I'm trying to build the Materialized.as DSL code here: https://kafka.apache.org/11/javadoc/org/apache/kafka/streams/state/Stores.html

But I'm getting the error

incompatible types: org.apache.kafka.common.serialization.Serde<java.lang.Long> cannot be converted to org.apache.kafka.common.serialization.Serde<java.lang.Object>

On the line

.withKeySerde(Serdes.Long())

Does anyone know what might be wrong here?

final StreamsBuilder builder = new StreamsBuilder();

   KeyValueBytesStoreSupplier storeSupplier = Stores.inMemoryKeyValueStore("mystore");
   KTable<Long,String> dataStore = builder.table(
     "example_stream",
     Materialized.as(storeSupplier)
             .withKeySerde(Serdes.Long())
             .withValueSerde(Serdes.String()));

Answer 1

The problem is that builder.table does not know the generic type defaulting to <Object,Object> . Later, the Serde types don't match. You need to specify the types like

KTable<Long,String> dataStore = builder.<Long,String>table(
    "example_stream",
    Materialized.as(storeSupplier)
        .withKeySerde(Serdes.Long())
        .withValueSerde(Serdes.String()));

Answer 2

I cannot say for sure without a code sample, however the error message is very clear. You are specifying to Kafka that the key is of type Long . However your key is actually some other Java Object. For example if you had a message with a String key, this code would change to: .withKeySerde(Serdes.String()) . Check the type of the key and specify the correct Serde for that type.