Declaring @Bean methods as 'static' is now permitted, whereas previously
it raised an exception at @Configuration class validation time.
A static @Bean method can be called by the container without requiring
the instantiation of its declaring @Configuration class. This is
particularly useful when dealing with BeanFactoryPostProcessor beans,
as they can interfere with the standard post-processing lifecycle
necessary to handle @Autowired, @Inject, @Value, @PostConstruct and
other annotations.
static @Bean methods cannot recieve CGLIB enhancement for scoping and
AOP concerns. This is acceptable in BFPP cases as they rarely if ever
need it, and should not in typical cases ever be called by another
@Bean method. Once invoked by the container, the resulting bean will
be cached as usual, but multiple invocations of the static @Bean method
will result in creation of multiple instances of the bean.
static @Bean methods may not, for obvious reasons, refer to normal
instance @Bean methods, but again this is not likely a concern for BFPP
types. In the rare case that they do need a bean reference, parameter
injection into the static @Bean method is technically an option, but
should be avoided as it will potentially cause premature instantiation
of more beans that the user may have intended.
Note particularly that a WARN-level log message is now issued for any
non-static @Bean method with a return type assignable to BFPP. This
serves as a strong recommendation to users that they always mark BFPP
@Bean methods as static.
See @Bean Javadoc for complete details.
Issue: SPR-8257, SPR-8269
Chris Beams