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From "Bill Bejeck (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (KAFKA-4125) Provide low-level Processor API meta data in DSL layer
Date Mon, 09 Jan 2017 19:17:58 GMT

    [ https://issues.apache.org/jira/browse/KAFKA-4125?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15812586#comment-15812586

Bill Bejeck commented on KAFKA-4125:

Is this task still viable/desired? If so I'll pick it up.

> Provide low-level Processor API meta data in DSL layer
> ------------------------------------------------------
>                 Key: KAFKA-4125
>                 URL: https://issues.apache.org/jira/browse/KAFKA-4125
>             Project: Kafka
>          Issue Type: Sub-task
>          Components: streams
>            Reporter: Matthias J. Sax
>            Assignee: Guozhang Wang
>            Priority: Minor
> 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,
> 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
> {noformat}
> V2 apply(V1 value);
> {noformat}
> 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
> {noformat}
> RichValueMapper<V1, V2> extends ValueMapper<V1, V2>, RichFunction
> {noformat}
> 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.

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