org.apache.kafka.streams.kstream

Interface Aggregator<K,V,VA>

Type Parameters:

K - key type

V - input value type

VA - aggregate value type

@InterfaceStability.Unstable
public interface Aggregator<K,V,VA>

The Aggregator interface for aggregating values of the given key. This is a generalization of Reducer and allows to have different types for input value and aggregation result. Aggregator is used in combination with Initializer that provides an initial aggregation value.

Aggregator can be used to implement aggregation functions like count.

See Also:

Initializer, KGroupedStream.aggregate(Initializer, Aggregator, org.apache.kafka.common.serialization.Serde, String), KGroupedStream.aggregate(Initializer, Aggregator, org.apache.kafka.streams.processor.StateStoreSupplier), KGroupedStream.aggregate(Initializer, Aggregator, Windows, org.apache.kafka.common.serialization.Serde, String), KGroupedStream.aggregate(Initializer, Aggregator, Windows, org.apache.kafka.streams.processor.StateStoreSupplier), KGroupedStream.aggregate(Initializer, Aggregator, Merger, SessionWindows, org.apache.kafka.common.serialization.Serde, String), KGroupedStream.aggregate(Initializer, Aggregator, Merger, SessionWindows, org.apache.kafka.common.serialization.Serde, org.apache.kafka.streams.processor.StateStoreSupplier), Reducer

Method Summary

Methods

Modifier and Type	Method and Description
VA	apply(K key, V value, VA aggregate) Compute a new aggregate from the key and value of a record and the current aggregate of the same key.

Method Detail

apply

VA apply(K key,
       V value,
       VA aggregate)

Compute a new aggregate from the key and value of a record and the current aggregate of the same key.

Parameters:

key - the key of the record

value - the value of the record

aggregate - the current aggregate value

Returns:

the new aggregate value