Spring Cloud Streams kafka binder - topic serialization configuration - spring

Question

So I think I've run myself into confusion as I understand there are two different kafka binders for SpringCloudStreams:
Spring Cloud Streams Kafka Binder
Spring Cloud Streams Kafka Streams Binder
I'm looking for the correct YAML settings to define the serializer and deserializer in the normal kafka binder for spring cloud streams:
I can tweak the defaults using this logic:
spring:
main:
web-application-type: NONE
application:
name: tbfm-translator
kafka:
consumer:
group-id: ${consumer_id}
bootstrap-servers: ${kafka_servers}
cloud:
schemaRegistryClient:
endpoint: ${schema_registry}
stream:
# default:
# producer.useNativeEncoding: true
# consumer.useNativeEncoding: true
defaultBinder: kafka
kafka:
binder:
auto-add-partitions: true # I wonder if its cause this is set
auto-create-topics: true # Disabling this seem to override the server setings and will auto create
producer-properties:
# For additional properties you can check here:
# https://docs.confluent.io/current/installation/configuration/producer-configs.html
schema.registry.url: ${schema_registry}
# Disable for auto schema registration
auto.register.schemas: false
# Use only the latest schema version
use.latest.version: true
# This will use reflection to generate schemas from classes - used to validate current data set
# against the scheam registry for valid production
schema.reflection: true
# To use an avro key enable the following line
#key.serializer: io.confluent.kafka.serializers.KafkaAvroSerializer
#This will use a string based key - aka not in the registry - dont need a name strategy with string serializer
key.serializer: org.apache.kafka.common.serialization.StringSerializer
# This will control the Serializer Setup
value.subject.name.strategy: io.confluent.kafka.serializers.subject.RecordNameStrategy
value.serializer: io.confluent.kafka.serializers.KafkaAvroSerializer
which is:
spring.cloud.stream.kafka.binder.producer-properties.value.serializer
spring.cloud.stream.kafka.binder.producer-properties.key.serializer
I figure I should be able to do this on a per-topic basis:
spring:
cloud:
stream:
bindings:
my-topic:
destination: a-topic
xxxxxxxx??
I've come across setting:
producer:
use-native-encoding: false
keySerde: <CLASS>
But this doesn't seem to be working. Is there an easy property I can set to do this on the per-topic basis? I think the keySerde is for the Kafka-streams implementation not the normal kafka binder.

Answer 1

use-native-encoding must be true to use your own serializers.
spring.cloud.stream.kafka.bindings.my-topic.producer.configuration.value.serializer: ...
See the documentation for kafka-specific producer properties.
configuration
Map with a key/value pair containing generic Kafka producer properties.
Default: Empty map.

Answer 2

stream:
bindings: # Define output topics here and then again in the kafka.bindings section
test:
destination: multi-output
producer:
useNativeDecoding: true
kafka:
bindings:
test:
destination: multi-output
producer:
configuration:
value.serializer: org.apache.kafka.common.serialization.StringSerializer
This seems to work - but very annoying I have to duplicate the binding definition in two places
Makes we want to shy away from the YAML style definition