Programming Grails

Chapter 4. Spring

Grails is a metaframework in that it ties together several other frameworks, and none is more pervasive in Grails than the Spring Framework. Grails uses a significant amount of Spring core functionality and optional modules including managing artifacts and many classes as Spring beans (using Spring’s dependency injection to manage the graph of dependencies), its datastore integration features (by default using its Hibernate integration), support for proxies and AOP to enable transparent transactions (and caching and security via plugins), internationalization, resource management, and a lot more.

In addition, there are many Spring extensions (both official and third party) that are readily usable in a Grails application. Many are already exposed via plugins (e.g., Spring Security), but if not, you can use an extension like you would in any Spring-based application. You can use annotated bean classes or the newer Java configuration, or copy bean definitions into grails-app/conf/spring/resources.xml (this isn’t created by default so you need to create it yourself) or convert them to Groovy syntax in resources.groovy. Register any dependencies in BuildConfig.groovy, and you’re ready to go.

Inversion of Control and Dependency Injection

One of the central ideas of Spring that Grails uses heavily is Inversion of Control (IoC), also known as Dependency Injection (DI). This reverses the direction of managing object dependencies from the older style of creating them directly ...