Status

Current state: Under Discussion

Discussion thread:

JIRA: here

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

As for now, KStream#print leads to a predefined output where key and value are printed with comma separation.
KAFKA-4830 suggests to extend print in a way that it takes KeyValueMapper as a parameter.
This will allow a user to change outputs according to the users demand.

Public Interfaces

The affected interface is KStream, which needs to be extended with another overloaded version of print:

void print(final Serde<K> keySerde,
           final Serde<V> valSerde,
           final String streamName,
           final KeyValueMapper<K, V, String> mapper);

Proposed Changes

See pull request GH-2669.
This PR contains a discussion regarding KAFKA-4830 as well as KAFKA-4772.

Compatibility, Deprecation, and Migration Plan

The extension of print will not introduce compatibility issues – we can maintain the current output by keeping the current output format as a default (if mapper was not set):

if(mapper == null) {
    printStream.println("[" + streamName + "]: " + keyToPrint + " , " + valueToPrint);
} else {
    printStream.println("[" + streamName + "]: " + mapper.apply(keyToPrint, valueToPrint));
}