org.apache.kafka.streams.kstream

Interface KeyValueMapper<K,V,VR>

Type Parameters:

K - key type

V - value type

VR - mapped value type

@InterfaceStability.Unstable
public interface KeyValueMapper<K,V,VR>

The KeyValueMapper interface for mapping a key-value pair to a new value of arbitrary type. For example, it can be used to

• map from an input KeyValue pair to an output KeyValue pair with different key and/or value type (for this case output type VR == KeyValue<NewKeyType,NewValueType>)
• map from an input record to a new key (with arbitrary key type as specified by VR)

This is a stateless record-by-record operation, i.e, apply(Object, Object) is invoked individually for each record of a stream (cf. Transformer for stateful record transformation). KeyValueMapper is a generalization of ValueMapper.

See Also:

ValueMapper, Transformer, KStream.map(KeyValueMapper), KStream.flatMap(KeyValueMapper), KStream.selectKey(KeyValueMapper), KStream.groupBy(KeyValueMapper), KStream.groupBy(KeyValueMapper, org.apache.kafka.common.serialization.Serde, org.apache.kafka.common.serialization.Serde), KTable.groupBy(KeyValueMapper), KTable.groupBy(KeyValueMapper, org.apache.kafka.common.serialization.Serde, org.apache.kafka.common.serialization.Serde), KTable.toStream(KeyValueMapper)

Method Summary

Methods

Modifier and Type	Method and Description
VR	apply(K key, V value) Map a record with the given key and value to a new value.

Method Detail

apply

VR apply(K key,
       V value)

Map a record with the given key and value to a new value.

Parameters:

key - the key of the record

value - the value of the record

Returns:

the new value