When to Write a Custom Serializer Spring Kafka ships JSON and Avro support. You need a custom serializer when: Your team uses Protobuf or MessagePack and wants native support You need a compact binary format for high-throughput topics (pricing ticks, sensor readings) You’re integrating with a legacy system that publishes a fixed binary protocol You want deterministic serialization for event deduplication or content-addressed storage The Serializer and Deserializer Interfaces // org.

The Serialization Problem Kafka stores bytes. KafkaTemplate<String, OrderPlacedEvent> needs to turn your Java object into bytes for the producer, and @KafkaListener needs to turn those bytes back into the right Java class on the consumer. Spring Kafka ships JsonSerializer and JsonDeserializer built on Jackson to handle this — but they have several sharp edges that break in real multi-service deployments. How Spring Kafka JSON Serialization Works flowchart LR subgraph Producer["Order Service"