Grails is actually a
Spring MVC application in disguise. Spring MVC is the Spring framework's built-in MVC web application framework. Although Spring MVC suffers from the same difficulties as frameworks like Struts in terms of its ease of use, it is superbly designed and architected and was, for Grails, the perfect framework to build another framework on top of.
Grails leverages Spring MVC in the following areas:
- Basic controller logic - Grails subclasses Spring's DispatcherServlet and uses it to delegate onto Grails controllers
- Data Binding and Validation - Grails' validation and data binding capabilities are built on those provided by Spring
- Runtime configuration - Grails' entire runtime convention based system is wired together by a Spring ApplicationContext
- Transactions - Grails uses Spring's transaction management in GORM
In other words Grails has Spring embedded running all the way through it.
The Grails ApplicationContext
Spring developers are often keen to understand how the Grails
ApplicationContext
instance is constructed. The basics of it are as follows.
- Grails constructs a parent
ApplicationContext
from the web-app/WEB-INF/applicationContext.xml
. This ApplicationContext
sets up the GrailsApplication instance and the GrailsPluginManager.
- Using this
ApplicationContext
as a parent Grails' analyses the conventions with the GrailsApplication
instance and constructs a child ApplicationContext
that is used as the root ApplicationContext
of the web application
Configured Spring Beans
Most of Grails' configuration happens at runtime. Each
plug-in may configure Spring beans that are registered with the
ApplicationContext
. For a reference as to which beans are configured refer to the reference guide which describes each of the Grails plug-ins and which beans they configure.