hello-service-auto-configuration's Introduction

Spring Custom Starter

From Brian Clozel, and Stéphane Nicoll talk on Spring Boot auto-configuration and the conditional configuration model.
Link to the presentation: https://www.infoq.com/presentations/spring-boot-auto-configuration

Key takeaways

There are two phases of how Spring Boot configure beans for an application
- 1st phase:
  - User annotated configuration will be given higher priority (those beans that are annotated in the application.)
  - Annotation: @ComponentScan
- 2nd phase:
  - AutoConfiguration based on the included *-starter modules and also Spring Boot self opinionated configuration.
  - Annoatation: @AutoConfiguration
Various type of @Conditional annotations that determines whether the beans should be initialised.
- The rest of the conditions wont be processed if the higher precedence conditional failed.
- Eg.
  - @ConditionalOnClass
  - @ConditionalOnMissingBean
  - @ConditionalOnProperty
  - @ConditionalOnExpression
Introduction @ConfigurationProperties and @EnableConfigurationProperties on how to create beans based on properties in application properties.
spring.factories under resources/META-INF/spring.factories.
- EnvironmentPostProcessor - post processing after the application context is loaded.
ApplicationEvent lifecycle.
Recommendation on fixing cyclic autoconfiguration problem
- @AutoConfigureAfter and @AutoConfigureBefore
Create customize condition by extending Spring condition
- Create new Annotation interface
- and condition implementation.
Making use of -Ddebug to show the loaded beans upon starting of the application
- or debug=true in the application.properties.