Spring Boot

In a Spring Boot service organized by technical layers (controller, service, repository, entity…), the business rule ends up next to JPA, Kafka and Jackson code. To test it, you start Spring, or you mock a large part of the framework. This post shows another way to organize the code, the hexagonal architecture, on a small and complete example: a service that reads sensor readings from Kafka, checks them and computes statistics. The domain and the use cases are plain Java, Spring, Kafka and JPA stay in adapters, and a test makes the build fail if this rule is broken. The code is in the tag phase-1 of the public repository iot-monitoring-platform, presented in the post Kafka and Spring Boot: a complete local project. ...

One service receives the readings of sensors; another one must process and store them. If the first one calls the second one over REST, the two are tied: when the second one is stopped or slow, the first one cannot deliver anything. Kafka sits between them: the first one publishes a message, the second one reads it at its own pace. This post builds that link from end to end, locally: Kafka in KRaft mode in Docker, a Spring Boot service that publishes a plain line of text, another one that reads it, and a page that shows the partition and the offset of each message. All the code is in the tag phase-1 of the public repository iot-monitoring-platform. ...