我正在学习Spring 3,我似乎没有掌握<context:annotation-config>和<context:component-scan>背后的功能。

从我读到的内容来看,它们似乎处理不同的注释(@Required, @Autowired等vs @Component, @Repository, @Service等),但从我读到的内容来看,它们注册了相同的bean后处理器类。

更让我困惑的是,在<context:component-scan>上有一个annotation-config属性。

有人能解释一下这些标签吗?什么是相似的,什么是不同的,是一个被另一个取代,它们互相完善,我需要其中一个吗,还是两个?


当前回答

您可以在spring上下文模式文件中找到更多信息。 以下内容来自spring-context-4.3.xsd

<conxtext:annotation-config />
Activates various annotations to be detected in bean classes: Spring's @Required and
@Autowired, as well as JSR 250's @PostConstruct, @PreDestroy and @Resource (if available),
JAX-WS's @WebServiceRef (if available), EJB 3's @EJB (if available), and JPA's
@PersistenceContext and @PersistenceUnit (if available). Alternatively, you may
choose to activate the individual BeanPostProcessors for those annotations.

Note: This tag does not activate processing of Spring's @Transactional or EJB 3's
@TransactionAttribute annotation. Consider the use of the <tx:annotation-driven>
tag for that purpose.
<context:component-scan>
Scans the classpath for annotated components that will be auto-registered as
Spring beans. By default, the Spring-provided @Component, @Repository, @Service, @Controller, @RestController, @ControllerAdvice, and @Configuration stereotypes    will be detected.

Note: This tag implies the effects of the 'annotation-config' tag, activating @Required,
@Autowired, @PostConstruct, @PreDestroy, @Resource, @PersistenceContext and @PersistenceUnit
annotations in the component classes, which is usually desired for autodetected components
(without external configuration). Turn off the 'annotation-config' attribute to deactivate
this default behavior, for example in order to use custom BeanPostProcessor definitions
for handling those annotations.

Note: You may use placeholders in package paths, but only resolved against system
properties (analogous to resource paths). A component scan results in new bean definitions
being registered; Spring's PropertySourcesPlaceholderConfigurer will apply to those bean
definitions just like to regular bean definitions, but it won't apply to the component
scan settings themselves.

其他回答

>激活bean中许多不同的注释,无论它们是用XML定义的还是通过组件扫描定义的。

>用于不使用XML定义bean

欲了解更多信息,请阅读:

3.9. 基于注释的容器配置 3.10. 类路径扫描和托管组件

<context:annotation-config>:扫描并激活spring config xml中已注册bean的注释。

<context:component-scan>: Bean注册+ <context:annotation-config>


@Autowired和@Required是目标属性级别,所以bean应该在使用这些注释之前在spring IOC中注册。要启用这些注释,要么必须注册各自的bean,要么包含<context:annotation-config />。例如,<context:annotation-config />仅适用于已注册的bean。

@Required启用RequiredAnnotationBeanPostProcessor处理工具 @Autowired启用AutowiredAnnotationBeanPostProcessor处理工具

注:注释本身没什么事,我们需要一个Processing Tool,它是底层的一个类,负责核心流程。


@Repository, @Service和@Controller是@Component,它们的目标是类级别。

<context:component-scan>它扫描包并找到并注册bean,它包括<context:annotation-config />所做的工作。

将XML迁移到注释

两者之间的区别真的很简单!

<context:annotation-config /> 

允许您使用仅限于连接bean的属性和构造函数的注释!

<context:component-scan base-package="org.package"/> 

启用<context:annotation-config />可以做的所有事情,添加使用原型,例如..@组件,@服务,@存储库。因此,您可以连接整个bean,而不仅仅局限于构造函数或属性!

您可以在spring上下文模式文件中找到更多信息。 以下内容来自spring-context-4.3.xsd

<conxtext:annotation-config />
Activates various annotations to be detected in bean classes: Spring's @Required and
@Autowired, as well as JSR 250's @PostConstruct, @PreDestroy and @Resource (if available),
JAX-WS's @WebServiceRef (if available), EJB 3's @EJB (if available), and JPA's
@PersistenceContext and @PersistenceUnit (if available). Alternatively, you may
choose to activate the individual BeanPostProcessors for those annotations.

Note: This tag does not activate processing of Spring's @Transactional or EJB 3's
@TransactionAttribute annotation. Consider the use of the <tx:annotation-driven>
tag for that purpose.
<context:component-scan>
Scans the classpath for annotated components that will be auto-registered as
Spring beans. By default, the Spring-provided @Component, @Repository, @Service, @Controller, @RestController, @ControllerAdvice, and @Configuration stereotypes    will be detected.

Note: This tag implies the effects of the 'annotation-config' tag, activating @Required,
@Autowired, @PostConstruct, @PreDestroy, @Resource, @PersistenceContext and @PersistenceUnit
annotations in the component classes, which is usually desired for autodetected components
(without external configuration). Turn off the 'annotation-config' attribute to deactivate
this default behavior, for example in order to use custom BeanPostProcessor definitions
for handling those annotations.

Note: You may use placeholders in package paths, but only resolved against system
properties (analogous to resource paths). A component scan results in new bean definitions
being registered; Spring's PropertySourcesPlaceholderConfigurer will apply to those bean
definitions just like to regular bean definitions, but it won't apply to the component
scan settings themselves.
<context:annotation-config/> <!-- is used to activate the annotation for beans -->
<context:component-scan base-package="x.y.MyClass" /> <!-- is for the Spring IOC container to look for the beans in the base package. -->

要注意的另一个重要点是context:component-scan隐式调用context:annotation-config来激活bean上的注释。如果你不想让context:component-scan隐式地为你激活注释,你可以继续将context:component-scan的annotation-config元素设置为false。

总结:

<context:annotation-config/> <!-- activates the annotations --> 
<context:component-scan base-package="x.y.MyClass" /> <!-- activates the annotations + register the beans by looking inside the base-package -->