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Status

Current state:  Under Discussion Accepted

Discussion thread: here

JIRA: here

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

Motivation

KStream#print() prints records on console; But the output from KStream#print() is fixed, some user maybe want to customize it.

To do this, one good method is KStream#print(KeyValueMapper<K, V, String>).

...

"[" + this.streamName + "]: " + mapper.apply(keyToPrint, valueToPrint)

Public Interfaces

...

With above idea, we also can apply this on KStream#writeAsText() to allow user customized output string written to file.

Public Interfaces

Expanding KStream#print() and KStream#writeAsText() which also need to be extended another version of print.

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

Proposed Changes

A straightforward first pass is on GitHub PR#3085.

Compatibility, Deprecation, and Migration Plan

No compatibility issues foreseen.

Rejected Alternatives

Base on KStream#print() and KStream#writeAsText(), some users seek for a new option which can customize the output but not should be restricted by fixed format.

To let user can customize output we think argument KStream#print() is  and KStream#writeAsText() is best option for usage(Intuition) and implementation(expand exist method with adding argument).