[jira] [Resolved] (KAFKA-10036) Improve error message if user violates `Supplier` pattern

["Matthias J. Sax (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KAFKA-10036?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Matthias J. Sax resolved KAFKA-10036.
-------------------------------------
    Fix Version/s: 2.8.0
       Resolution: Fixed

> Improve error message if user violates `Supplier` pattern
> ---------------------------------------------------------
>
>                 Key: KAFKA-10036
>                 URL: https://issues.apache.org/jira/browse/KAFKA-10036
>             Project: Kafka
>          Issue Type: Improvement
>          Components: streams
>            Reporter: Matthias J. Sax
>            Assignee: Igor Soarez
>            Priority: Minor
>              Labels: newbie
>             Fix For: 2.8.0
>
>
> Using the Processor API, users need to pass in a `ProcessorSupplier` that needs to return new `Processor` instance each time `get()` is called.
> Users violate this rule on a regular basis and return the same instance on `get()`. This mistake leads to a (not very informative) `NullPointerException` during runtime. (Cf: [https://stackoverflow.com/questions/61790984/kafka-stream-forward-method-throwing-nullpointerexception-because-processornode/61978396)]
> We could improve the error message by checking if `currentNode()` returns `null` ([https://github.com/apache/kafka/blob/2.4/streams/src/main/java/org/apache/kafka/streams/processor/internals/ProcessorContextImpl.java#L183)] and throw an informative error message for this case.
> Furthermore, we could do a "sanity" check within `KafkaStreams` constructor before we start the process threads: we get all `Suppliers` for the `Topology` and call `get()` two times on each supplier to compare if the returned object references are different – if they are the same, we throw an informative error message.
> We should improve the JavaDocs, too: [https://github.com/apache/kafka/blob/2.4/streams/src/main/java/org/apache/kafka/streams/processor/ProcessorSupplier.java#L34] (also for `Transformer` et al. – it seems to be too subtle what "new" means. Similarly for [https://github.com/apache/kafka/blob/2.4/streams/src/main/java/org/apache/kafka/streams/Topology.java] and [https://github.com/apache/kafka/blob/2.4/streams/src/main/java/org/apache/kafka/streams/kstream/KStream.java] (`process()`, `transform()` etc.)
> Furthermore, we should improve the docs: to explain the supplier pattern explicitly: [https://kafka.apache.org/25/documentation/streams/developer-guide/processor-api.html]



--
This message was sent by Atlassian Jira
(v8.3.4#803005)