What is the spring-boot-configuration-processor ? Why do people exclude libraries from it? Why is it invisible in dependency tree?

Menios :

Introduction

So I noticed the following line in the gradle file of the jhipster project:

annotationProcessor ("org.springframework.boot:spring-boot-configuration-processor") {
        exclude group: 'com.vaadin.external.google', module: 'android-json'
    }

https://github.com/jhipster/jhipster-sample-app-gradle/blob/9e9c3db8f3bedba4b1efd85ecb6ff3f12a5f596a/build.gradle#L230

We also used the same configuration in Maven for another project to solve the following problem: Maven transient dependency (library/jar vaadin json) is not being excluded

Questions

And now I have the following questions:

• What does the spring-boot-configuration-processor dependency do?
• Why is it necessary to sometimes exclude dependencies from the processor?
• Why doesn't the processor necessarily appear in the mvn-dependency tree?
• Why are exclusions used with processor in situations where it's very difficult to exclude a dependency?

Andy Wilkinson :

spring-boot-configuration-processor is an annotation processor that generates metadata about classes in your application that are annotated with @ConfigurationProperties. This metadata is used by your IDE (Eclipse, IntelliJ, or NetBeans) to provide auto-completion and documentation for the properties when editing application.properties and application.yaml files. You can learn a bit more about it in the relevant section of Spring Boot's reference documentation.

Since Spring Boot 1.5.10, the exclusion is no longer necessary as com.vaadin.external.google:android-json is no longer a dependency of spring-boot-configuration-processor.