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https://issues.apache.org/jira/browse/KAFKA-4612?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15819196#comment-15819196
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Kurt Ostfeld commented on KAFKA-4612:
-------------------------------------
Thank you so much! That all makes perfect sense.
> Simple Kafka Streams app causes "ClassCastException: java.lang.String cannot
> be cast to [B"
> -------------------------------------------------------------------------------------------
>
> Key: KAFKA-4612
> URL: https://issues.apache.org/jira/browse/KAFKA-4612
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Affects Versions: 0.10.1.1
> Environment: Virtual Machine using Debian 8 + Confluent Platform
> 3.1.1.
> Reporter: Kurt Ostfeld
> Attachments: KafkaIsolatedBug.tar.gz
>
>
> I've attached a minimal single source file project that reliably reproduces
> this issue.
> This project does the following:
> 1) Create test input data. Produces a single random (String,String) record
> into two diferent topics "topicInput" and "topicTable"
> 2) Creates and runs a Kafka Streams application:
> val kafkaTable: KTable[String, String] = builder.table(Serdes.String,
> Serdes.String, "topicTable", "topicTable")
> val incomingRecords: KStream[String, String] =
> builder.stream(Serdes.String, Serdes.String, "topicInput")
> val reKeyedRecords: KStream[String, String] =
> incomingRecords.selectKey((k, _) => k)
> val joinedRecords: KStream[String, String] =
> reKeyedRecords.leftJoin(kafkaTable, (s1: String, _: String) => s1)
> joinedRecords.to(Serdes.String, Serdes.String, "topicOutput")
> This reliably generates the following error:
> [error] (StreamThread-1) java.lang.ClassCastException: java.lang.String
> cannot be cast to [B
> java.lang.ClassCastException: java.lang.String cannot be cast to [B
> at
> org.apache.kafka.common.serialization.ByteArraySerializer.serialize(ByteArraySerializer.java:18)
> at
> org.apache.kafka.streams.processor.internals.RecordCollectorImpl.send(RecordCollectorImpl.java:63)
> at
> org.apache.kafka.streams.processor.internals.SinkNode.process(SinkNode.java:82)
> at
> org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:202)
> at
> org.apache.kafka.streams.kstream.internals.KStreamFilter$KStreamFilterProcessor.process(KStreamFilter.java:44)
> at
> org.apache.kafka.streams.processor.internals.ProcessorNode.process(ProcessorNode.java:82)
> at
> org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:202)
> at
> org.apache.kafka.streams.kstream.internals.KStreamMap$KStreamMapProcessor.process(KStreamMap.java:43)
> at
> org.apache.kafka.streams.processor.internals.ProcessorNode.process(ProcessorNode.java:82)
> at
> org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:202)
> at
> org.apache.kafka.streams.processor.internals.SourceNode.process(SourceNode.java:66)
> at
> org.apache.kafka.streams.processor.internals.StreamTask.process(StreamTask.java:180)
> at
> org.apache.kafka.streams.processor.internals.StreamThread.runLoop(StreamThread.java:436)
> at
> org.apache.kafka.streams.processor.internals.StreamThread.run(StreamThread.java:242)
> One caveat: I'm running this on a Confluent Platform 3.1.1 instance which
> uses Kafka 0.10.1.0 since there is no newer Confluent Platform available. The
> Kafka Streams project is built using "kafka-clients" and "kafka-streams"
> version 0.10.1.1. If I use 0.10.1.0, I reliably hit bug
> https://issues.apache.org/jira/browse/KAFKA-4355. I am not sure if there is
> any issue using 0.10.1.1 libraries with a Confluent Platform running Kafka
> 0.10.1.0. I will obviously try the next Confluent Platform binary when it is
> available.
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