Package org.apache.kafka.streams.kstream

Interface Aggregator<K,V,VAgg>

Type Parameters:

K - key type

V - input value type

VAgg - aggregate value type

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

@FunctionalInterface
public interface Aggregator<K,V,VAgg>

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)
• KGroupedStream.aggregate(Initializer, Aggregator, Materialized)
• TimeWindowedKStream.aggregate(Initializer, Aggregator)
• TimeWindowedKStream.aggregate(Initializer, Aggregator, Materialized)
• SessionWindowedKStream.aggregate(Initializer, Aggregator, Merger)
• SessionWindowedKStream.aggregate(Initializer, Aggregator, Merger, Materialized)
• Reducer

Method Summary

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

Method Details

apply

VAgg apply(K key,
 V value,
 VAgg 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