# kafka4-migration: Spring Kafka 3 to 4 on Spring Boot 3.5 to 4.1

Companion code for the ankurm.com post "Spring Kafka 3 to 4 Migration Guide".

| Folder | What it is |
|---|---|
| `legacy/` | Producer, `@KafkaListener` and an `@EmbeddedKafka` test on Boot 3.5.16 / Spring Kafka 3.3.16 / kafka-clients 3.9.2 (JDK 21), using the Jackson 2 `JsonSerializer` |
| `migrated/` | The same app on Boot 4.1.1 / Spring Kafka 4.1.1 / kafka-clients 4.2.1 (JDK 25), using `spring-boot-starter-kafka` and `JacksonJsonSerializer` |
| `scripts/run-all.sh` | Builds the intermediate stages from `legacy/` and regenerates every file in `output/` |
| `output/` | Transcripts for each stage |

Spring Kafka 4.1.1 is the latest GA; 4.2.0-M1 and 4.2.0-M2 are milestones and are not tested here.
No external broker is needed: the tests use `@EmbeddedKafka`. Tested on 28 September 2026.