# spring-messaging-demo

Companion code for the messaging series on [ankurm.com](https://ankurm.com). Each directory is a
self-contained Maven project for one article, with its own `pom.xml`, its own numbered
documentation chapters, and its own captured output under `docs/output/` — regenerated by that
module's `scripts/run-all.sh`, never typed by hand.

| Module | Article | What it demonstrates |
|---|---|---|
| [`kafka-basics/`](kafka-basics/README.md) | [Spring Boot 4.1 and Apache Kafka: Producer, Consumer and Serialisation from Scratch](https://ankurm.com/spring-boot-4-1-kafka-producer-consumer-serialisation/) | The on-ramp: what the starter gives you, the two Jackson serializer families, where a key lands and why, and which defaults are Kafka's rather than Spring's |
| [`kafka-error-handling/`](kafka-error-handling/README.md) | [Kafka Error Handling with Spring Kafka 4.1: DLT, Retry Topics and Poison Pills](https://ankurm.com/spring-kafka-4-1-error-handling-dlt-retry-topics/) | What the default error handler really does, why a poison pill stops a partition, and what blocking retries cost that retry topics do not |
| [`rabbitmq/`](rabbitmq/README.md) | [Spring Boot and RabbitMQ: Exchanges, Queues, Bindings and a Working Dead-Letter Queue](https://ankurm.com/spring-boot-rabbitmq-exchanges-dead-letter-queue/) | All four exchange types against a real broker, manual acknowledgement, and a dead-letter path exercised through both rejection and TTL expiry |

The two brokers make an instructive pair. Kafka's consumer holds an offset and the broker
remembers nothing about individual records; RabbitMQ's broker owns the message until it is
acknowledged and can route, expire and dead-letter it on its own. Almost every difference in how
you handle failure follows from that one sentence — which is why Kafka needs a retry topic
to do what RabbitMQ does with a queue argument.

They are meant to be read in order. `kafka-basics` establishes that the default acknowledgement
mode is `BATCH` and therefore that delivery is at-least-once; everything the error-handling
module does exists because of that one sentence.

## Common ground

All modules target the same verified stack: **JDK 25** (Temurin 25.0.4.1+1), **Spring Boot
4.1.1**, **Spring Framework 7.0.9**. Versions were read from `maven-metadata.xml` on Maven
Central and from Boot's own `spring-boot-dependencies` POM, rather than from release
announcements.

Every module runs its broker without Docker, so the transcripts can be regenerated on any
machine with a JDK: Kafka via the in-process KRaft broker in `spring-kafka-test`, RabbitMQ via a
real broker started by the module's own scripts. Each module also ships a Testcontainers
configuration for the cases where the deployed image is what you need to test against.

## Licence

MIT — see [LICENSE](LICENSE).