[Module README](../README.md) · [Exchanges →](02-exchanges.md)

# 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.

```xml
<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`:

```java
@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.

[Exchanges &rarr;](02-exchanges.md)