spring-messaging-demo/rabbitmq/docs/01-the-on-ramp.md

Module README · Exchanges →

1. The on-ramp

Two dependency decisions decide whether anything works, and neither produces a helpful error.

Use the starter, not spring-rabbit

Boot 4 moved every auto-configuration out of spring-boot-autoconfigure into a per-technology module. RabbitMQ's lives in spring-boot-amqp, package org.springframework.boot.amqp.autoconfigure, and a bare org.springframework.amqp:spring-rabbit dependency does not bring it. You get no RabbitTemplate, no RabbitAdmin, no listener container factory — and a context that starts cleanly.

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-amqp</artifactId>
</dependency>

Boot does not give you a JSON converter

Spring Kafka defaults to serializers you configure. Spring AMQP defaults to SimpleMessageConverter, which handles String, byte[] and Serializable and refuses everything else:

IllegalArgumentException: SimpleMessageConverter only supports String, byte[] and
Serializable payloads, received: com.ankurm.rabbit.OrderMessage

One bean fixes both directions, because the auto-configured RabbitTemplate and the listener container factory both look for a MessageConverter:

@Bean
MessageConverter messageConverter() {
    return new JacksonJsonMessageConverter();
}

Note the class name. Spring AMQP 4.1 ships Jackson2JsonMessageConverter (Jackson 2) and JacksonJsonMessageConverter (Jackson 3) side by side — exactly as Spring Kafka ships JsonSerializer and JacksonJsonSerializer. Boot 4 is a Jackson 3 application. The rule across both stacks is the same: if the class name contains a 2, it belongs to the previous major version of Jackson.

Versions

Boot 4.1.1 manages Spring AMQP 4.1.1 and com.rabbitmq:amqp-client 5.30.0. Maven Central has amqp-client 5.35.0; overriding the managed version to reach it is a change you should have a reason for.

One API change to know about: RabbitAdmin.QUEUE_MESSAGE_COUNT now holds a Long. Every older example casts it to Integer, which is a ClassCastException at runtime and not at compile time.

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