Description
For Processor API, user can get meta data like record offset, timestamp etc via the provided Context object. It might be useful to allow uses to access this information in DSL layer, too.
The idea would be, to do it "the Flink way", ie, by providing
RichFunctions; mapValue() for example.
Is takes a ValueMapper<V1, V2> that only has method
V2 apply(V1 value);
Thus, you cannot get any meta data within apply (it's completely "blind").
We would add two more interfaces: RichFunction with a method
open(Context context) and
RichValueMapper<V1, V2> extends ValueMapper<V1, V2>, RichFunction
This way, the user can chose to implement Rich- or Standard-function and
we do not need to change existing APIs. Both can be handed into
KStream.mapValues() for example. Internally, we check if a Rich
function is provided, and if yes, hand in the Context object once, to
make it available to the user who can now access it within apply() – or
course, the user must set a member variable in open() to hold the
reference to the Context object.
KIP: https://cwiki.apache.org/confluence/display/KAFKA/KIP-159%3A+Introducing+Rich+functions+to+Streams
Attachments
Issue Links
- blocks
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KAFKA-5267 Simplify KStreamPrint using RichFunctions
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- Open
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- relates to
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KAFKA-5632 Message headers not supported by Kafka Streams
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- Resolved
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- mentioned in
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