Jouni created KAFKA-7371:
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Summary: Finally deprecate
org.apache.kafka.common.serialization.ExtendedSerializer
Key: KAFKA-7371
URL: https://issues.apache.org/jira/browse/KAFKA-7371
Project: Kafka
Issue Type: Wish
Components: streams
Affects Versions: 2.0.0
Reporter: Jouni
As mentioned in the javadocs "Once Kafka drops support for Java 7, the
serialize()} method introduced by this interface will be added to Serializer
with a default implementation so that backwards compatibility is maintained.
This interface may be deprecated once that happens.". Support for Java 7 was
already dropped in Kafka 2.0.0 but this hasn't yet happened.
The problem is that some out-of-project external serializers (for example,
org.springframework.kafka.support.serializer.JsonSerializer, quite commonly
used) already do add message headers when using producer API, one of those
being __TypeId__, which contains the java class name. But when using streams
DSL, there's no way to either access or modify those headers, and according to
KIP-244, they get just copied to the sink. Also, because in
RecordCollectorImpl.send there are calls
final byte[] keyBytes = keySerializer.serialize(topic, key);
final byte[] valBytes = valueSerializer.serialize(topic, value);
and not
final byte[] keyBytes = keySerializer.serialize(topic, headers, key);
final byte[] valBytes = valueSerializer.serialize(topic, headers, value);
which would be possible when the plain Serializer gets the default method
added. So, currently, there's no way for anyone to write a serializer that
modifies the headers if necessary when using streams.
In my case, the problem occurred when transforming an object from input stream
to a different type of object in output stream. Took a while to debug where did
those (wrong) headers come from, and either disable adding those headers on
producer side, or as I happened to be using Processor API, modify myself the
headers in ProcessorContext.
An unfortunate side-effect of two different projects making decisions affecting
each other. Not exactly a bug in either one, but a really big nuisance to find
out what's happening. I'd prefer things working as much as possible mostly
out-of-the-box. Ok, API changes must sometimes just be made.
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