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

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1. The on-ramp, and the dependency that is not the one you remember

Under Spring Boot 3 you added org.springframework.kafka:spring-kafka and got a KafkaTemplate. Under Boot 4 you get this:

No qualifying bean of type 'org.springframework.kafka.core.KafkaTemplate<java.lang.String,
com.ankurm.kafkabasics.OrderEvent>' available

Boot 4 split the auto-configurations out of spring-boot-autoconfigure into per-technology modules. Kafka's now lives in spring-boot-kafka, package org.springframework.boot.kafka.autoconfigure, and a bare spring-kafka dependency does not bring it. The application compiles, the context starts, and there is simply no template.

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

That is the fix, and the same shape applies elsewhere: spring-boot-starter-amqp for RabbitMQ, spring-boot-starter-restclient for RestClient.Builder. The rule of thumb for Boot 4 is that if you are depending on a library directly rather than through a Boot starter, you are probably missing its auto-configuration.

What the starter actually gives you

Bean	Comes from	Notes
KafkaTemplate<?, ?>	KafkaAutoConfiguration	typed by your injection point
ProducerFactory / ConsumerFactory	KafkaAutoConfiguration	built from spring.kafka.*
KafkaListenerContainerFactory	KafkaAnnotationDrivenConfiguration	what @KafkaListener binds to
KafkaAdmin	KafkaAutoConfiguration	creates NewTopic beans at startup

KafkaAdmin is worth knowing about early: declare a NewTopic bean and Boot creates the topic on startup with the partition count and replication factor you asked for. It will not change an existing topic's partition count, so a NewTopic bean that disagrees with the cluster is silently ignored rather than applied.

Versions

Boot 4.1.1 manages Spring Kafka 4.1.1 and kafka-clients 4.2.1. Note the second one: Maven Central has kafka-clients 4.3.1, and overriding the managed version to reach it is the kind of change that works until it does not. Let the BOM decide.

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