注释类型 Conditional

@Target({TYPE,METHOD})
@Retention(RUNTIME)
@Documented
public @interface Conditional

Indicates that a component is only eligible for registration when all specified conditions match.

A condition is any state that can be determined programmatically before the bean definition is due to be registered (see Condition for details).

The @Conditional annotation may be used in any of the following ways:

• as a type-level annotation on any class directly or indirectly annotated with @Component, including @Configuration classes
• as a meta-annotation, for the purpose of composing custom stereotype annotations
• as a method-level annotation on any @Bean method

If a @Configuration class is marked with @Conditional, all of the @Bean methods, @Import annotations, and @ComponentScan annotations associated with that class will be subject to the conditions.

NOTE: Inheritance of @Conditional annotations is not supported; any conditions from superclasses or from overridden methods will not be considered. In order to enforce these semantics, @Conditional itself is not declared as @Inherited; furthermore, any custom composed annotation that is meta-annotated with @Conditional must not be declared as @Inherited.