All Implemented Interfaces and Traits:

EnvironmentAware, BeanFactoryPostProcessor

@Configuration(proxyBeanMethods = false)
@ConditionalOnMissingBean(name = "sitemesh3")
protected static class GspAutoConfiguration.Sitemesh3Configuration
extends java.lang.Object
implements EnvironmentAware, BeanFactoryPostProcessor

Applies the SiteMesh defaults to the environment of a context that was not built by SpringApplication, where Sitemesh3EnvironmentPostProcessor - which applies them to every application that was - does not run.

It is a BeanFactoryPostProcessor so that it is instantiated, and so applies the defaults through EnvironmentAware, before anything reads a SiteMesh property; the post-processing itself has nothing to do. It declares no beans, so it is not proxied - which also settles the warning that being created this early otherwise draws.