@org.springframework.boot.autoconfigure.AutoConfiguration
@org.springframework.boot.autoconfigure.AutoConfigureAfter(name = "org.springframework.boot.webmvc.autoconfigure.DispatcherServletAutoConfiguration")
@org.springframework.boot.autoconfigure.AutoConfigureBefore(name = "org.sitemesh.autoconfigure.SiteMeshViewResolverAutoConfiguration")
@org.springframework.boot.autoconfigure.condition.ConditionalOnClass(SiteMeshViewResolverBeanPostProcessor.class)
@org.springframework.boot.autoconfigure.condition.ConditionalOnProperty(name = "sitemesh.integration", havingValue = "view-resolver", matchIfMissing = true)
public class Sitemesh3AutoConfiguration
extends java.lang.Object

Registers the Grails SiteMesh 3 integration beans ahead of the upstream auto-configuration: the GrailsSiteMeshViewResolverBeanPostProcessor, the CaptureAwareContentProcessor (contentProcessor) and the Sitemesh3LayoutFinder (decoratorSelector).

Upstream's SiteMeshViewResolverAutoConfiguration declares each of these with a @ConditionalOnMissingBean guard. By scheduling this configuration first (via AutoConfigureBefore) the Grails implementations are registered before those guards are evaluated, so the upstream defaults back off cleanly rather than being registered and then overridden after the fact.

The contentProcessor and decoratorSelector beans drive view decoration, which is only meaningful when Spring MVC is resolving views, so they are gated on a DispatcherServlet being present. This keeps them out of the lightweight unit-test contexts built by grails-testing-support, which have no dispatcher servlet.