org.apache.kafka.streams.kstream

Interface Transformer<K,V,R>

Type Parameters:

K - key type

V - value type

R - return type

public interface Transformer<K,V,R>

A stateful Transformer interface for transform a key-value pair into a new value.

Method Summary

Methods

Modifier and Type	Method and Description
void	close() Close this processor and clean up any resources.
void	init(ProcessorContext context) Initialize this transformer with the given context.
R	punctuate(long timestamp) Perform any periodic operations and possibly generate a key, if this processor schedule itself with the context during initialization.
R	transform(K key, V value) Transform the record with the given key and value.

Method Detail

init

void init(ProcessorContext context)

Initialize this transformer with the given context. The framework ensures this is called once per processor when the topology that contains it is initialized.

If this transformer is to be called periodically by the framework, then this method should schedule itself with the provided context.

Parameters:

context - the context; may not be null

transform

R transform(K key,
          V value)

Transform the record with the given key and value.

Parameters:

key - the key for the record

value - the value for the record

Returns:

new value; if null no key-value pair will be forwarded to down stream

punctuate

R punctuate(long timestamp)

Perform any periodic operations and possibly generate a key, if this processor schedule itself with the context during initialization.

Parameters:

timestamp - the stream time when this method is being called

Returns:

new value; if null it will not be forwarded to down stream

close

void close()

Close this processor and clean up any resources.