Status
Current state: Discarded (duplicated by KIP-160)
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:
"[" + this.streamName + "]: " + keyToPrint + " , " + valueToPrint
We therefore suggest to extend print
in a way that it takes KeyValueMapper
as a parameter, to let the user modify the output according to its needs. If a mapper is present, the hard-coded key-value output can be replaced with:
"[" + this.streamName + "]: " + mapper.apply(keyToPrint, valueToPrint)
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
Apart from the extension of the interface, the previous implementation of print
will be call a new overloaded version thereof. In case no KeyValuemapper
is set, null
serves as the indicator to use the default output:
@Override public void print(Serde<K> keySerde, Serde<V> valSerde, String streamName) { print(keySerde, valSerde, streamName, null); } @Override public void print(final Serde<K> keySerde, final Serde<V> valSerde, String streamName, final KeyValueMapper<K, V, String> mapper){ ...
Compatibility, Deprecation, and Migration Plan
The extension of print
will not introduce compatibility issues. Further more, 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)); }