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Annotation-based Container Configuration

Spring provides comprehensive support for annotation-based configuration, operating on metadata in the component class itself by using annotations on the relevant class, method, or field declaration. As mentioned in Example: The AutowiredAnnotationBeanPostProcessor, Spring uses BeanPostProcessors in conjunction with annotations to make the core IOC container aware of specific annotations.

For example, the @Autowired annotation provides the same capabilities as described in Autowiring Collaborators but with more fine-grained control and wider applicability. In addition, Spring provides support for JSR-250 annotations, such as @PostConstruct and @PreDestroy, as well as support for JSR-330 (Dependency Injection for Java) annotations contained in the jakarta.inject package such as @Inject and @Named. Details about those annotations can be found in the relevant section.

Annotation injection is performed before external property injection. Thus, external configuration (e.g. XML-specified bean properties) effectively overrides the annotations for properties when wired through mixed approaches.

Technically, you can register the post-processors as individual bean definitions, but they are implicitly registered in an AnnotationConfigApplicationContext already.

In an XML-based Spring setup, you may include the following configuration tag to enable mixing and matching with annotation-based configuration:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:context="http://www.springframework.org/schema/context"
	xsi:schemaLocation="http://www.springframework.org/schema/beans
		https://www.springframework.org/schema/beans/spring-beans.xsd
		http://www.springframework.org/schema/context
		https://www.springframework.org/schema/context/spring-context.xsd">

	<context:annotation-config/>

</beans>

The <context:annotation-config/> element implicitly registers the following post-processors:

<context:annotation-config/> only looks for annotations on beans in the same application context in which it is defined. This means that, if you put <context:annotation-config/> in a WebApplicationContext for a DispatcherServlet, it only checks for @Autowired beans in your controllers, and not your services. See The DispatcherServlet for more information.