Extended coverage of full vs lite mode for configuration classes

Issue: SPR-16076
This commit is contained in:
Juergen Hoeller 2017-10-16 23:02:35 +02:00
parent 77bab959a3
commit 17fb4fed09
1 changed files with 22 additions and 12 deletions

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@ -4626,6 +4626,7 @@ The corresponding bean definitions appear as follows.
----
[[beans-autowired-annotation-qualifiers]]
=== Fine-tuning annotation-based autowiring with qualifiers
@ -5043,7 +5044,6 @@ Generic qualifiers also apply when autowiring Lists, Maps and Arrays:
[[beans-custom-autowire-configurer]]
=== CustomAutowireConfigurer
@ -6138,27 +6138,37 @@ The `AppConfig` class above would be equivalent to the following Spring `<beans/
</beans>
----
.Full @Configuration vs 'lite' @Beans mode?
.Full @Configuration vs 'lite' @Bean mode?
****
When `@Bean` methods are declared within classes that are __not__ annotated with
`@Configuration` they are referred to as being processed in a 'lite' mode. For example,
bean methods declared in a `@Component` or even in a __plain old class__ will be
considered 'lite'.
`@Configuration` they are referred to as being processed in a 'lite' mode. Bean methods
declared in a `@Component` or even in a __plain old class__ will be considered 'lite',
with a different primary purpose of the containing class and an `@Bean` method just
being a sort of bonus there. For example, service components may expose management views
to the container through an additional `@Bean` method on each applicable component class.
In such scenarios, `@Bean` methods are a simple general-purpose factory method mechanism.
Unlike full `@Configuration`, lite `@Bean` methods cannot easily declare inter-bean
dependencies. Usually one `@Bean` method should not invoke another `@Bean` method when
operating in 'lite' mode.
Unlike full `@Configuration`, lite `@Bean` methods cannot declare inter-bean dependencies.
Instead, they operate on their containing component's internal state and optionally on
arguments that they may declare. Such an `@Bean` method should therefore not invoke other
`@Bean` methods; each such method is literally just a factory method for a particular
bean reference, without any special runtime semantics. The positive side-effect here is
that no CGLIB subclassing has to be applied at runtime, so there are no limitations in
terms of class design (i.e. the containing class may nevertheless be `final` etc).
Only using `@Bean` methods within `@Configuration` classes is a recommended approach of
ensuring that 'full' mode is always used. This will prevent the same `@Bean` method from
accidentally being invoked multiple times and helps to reduce subtle bugs that can be
hard to track down when operating in 'lite' mode.
In common scenarios, `@Bean` methods are to be declared within `@Configuration` classes,
ensuring that 'full' mode is always used and that cross-method references will therefore
get redirected to the container's lifecycle management. This will prevent the same
`@Bean` method from accidentally being invoked through a regular Java call which helps
to reduce subtle bugs that can be hard to track down when operating in 'lite' mode.
****
The `@Bean` and `@Configuration` annotations will be discussed in depth in the sections
below. First, however, we'll cover the various ways of creating a spring container using
Java-based configuration.
[[beans-java-instantiating-container]]
=== Instantiating the Spring container using AnnotationConfigApplicationContext