The Spring Framework is a de facto standard for creating enterprise java applications as it offers a broad variety of functionality for all kinds of needs. Things became even more convenient when Spring Boot was introduced some years ago.
Have you ever wondered about all tha magic that comes with Spring? Just add a dependency or an annotation and BAHMM! there you go! A lot of this magic is based on the various Starters that are offered for Spring Boot. Starters are the way to go when it comes to creating shared components in the Spring Boot universe. So it might be something worth spending the effort on creating your own! Unfortunately the official documentation is a little short and left some questions open to me. Most tutorials that can be found on the web describe how to create a starter using Maven. As I mostly use Gradle I had a hard time transforming these tutorials.
This project demonstrates how to create a custom spring boot starter using Gradle.
Spring Boot starters require a certain project structure. To fit this need you need to author a Multi-Project Build containing at least three modules:
1. gradle-spring-boot-starter-sample (This project provides necessary dependencies and gradle configuration)
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|-> 2. my-library-autoconfigure (This project holds spring boot autoconfiguration)
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|-> 3. my-library (T his project holds you actual business logic)
The top-level project is mainly used to configure some common properties and to define a dependency on the Auto-configuration
Auto-configuration is where the magic happens. Especially the various @ConditionalOnXXX annotations are used to provide both a reasonable
default configuration as well as flexibility at the same time.
Integration of a custom library needs extra efforts and configuration to work with you Spring Configuration. Even if you properly define Spring components using the known
Spring stereotype annotations like @Service or @Component Spring will not create bean instances as it will not be aware of you classes. You will need to add the corresponding packages
to Spring's component scan manually using @ComponentScan annotation. This is usually some how error prone
and feels somehow strange.
Using Spring Boot Starters using @ComponentScan but how the heck is Spring finding your Bean definitions? This is done by providing a spring.factories file under src/main/resources/META-INF/spring.factories in your Auto-configuration project telling Spring what it needs to know:
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
net.skobow.samples.mylibrary.autoconfigure.MyLibraryAutoConfiguration
Your shred component goes into the third project that needs to be referenced by the Auto-configuration
Feedback is very welcome! Please send your feedback and questions to sk@skobow.net
