@Bean、@Component、 @Service、 @Repository 和 @Controller注解的区别

客官°小女子只卖身不卖艺 2022-05-11 15:54 241阅读 0赞

@Bean：表示一个方法实例化、配置或者初始化一个Spring IoC容器管理的新对象。  
@Component: 自动被comonent扫描。 表示被注解的类会自动被component扫描  
@Repository: 用于持久层，主要是数据库存储库。  
@Service: 表示被注解的类是位于业务层的业务component。  
@Controller:表明被注解的类是控制component，主要用于展现层 。

**@Bean与@Component区别**  
@Component是 spring 2.5引入的，为了摆脱通过classpath扫描根据xml方式定义的bean的方式.

@Bean是spring 3.0 引入的，和 @Configuration一起工作，为了摆脱原先的xml和java config方式。

Spring管理Bean方式有两种，一种是注册Bean，一种装配Bean。  
可以通过三种方式实现bean管理，一使用自动配置的方式、二使用JavaConfig的方式、三使用XML配置的方式。

@Compent 作用就相当于 XML配置

@Component
    @Data
    public class User{ 
        private String name = "tom";
    }

@Bean 需要在配置类中使用，即类上需要加上@Component或者@Configuration注解， 通常加上@Configuration。 @Bean的用法在[这里][Link 1]。

@Configuration
    public class AppConfig { 
    
        @Bean
        public TransferServiceImpl transferService() { 
            return new TransferServiceImpl();
        }
    }

官方文档在[这里。][Link 2]

两者都可以通过[@Autowired][Autowired]装配

@Autowired
    private TransferService transferService;

**@Component与@Service区别**  
目前基本没有区别。  
参看源代码spring-context-4.3.16

/** * Indicates that an annotated class is a "Service", originally defined by Domain-Driven * Design (Evans, 2003) as "an operation offered as an interface that stands alone in the * model, with no encapsulated state." * * <p>May also indicate that a class is a "Business Service Facade" (in the Core J2EE * patterns sense), or something similar. This annotation is a general-purpose stereotype * and individual teams may narrow their semantics and use as appropriate. * * <p>This annotation serves as a specialization of {@link Component @Component}, * allowing for implementation classes to be autodetected through classpath scanning. * * @author Juergen Hoeller * @since 2.5 * @see Component * @see Repository */
    @Target({ ElementType.TYPE})
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Component
    public @interface Service { 
    
    	/** * The value may indicate a suggestion for a logical component name, * to be turned into a Spring bean in case of an autodetected component. * @return the suggested component name, if any (or empty String otherwise) */
    	String value() default "";
    
    }

从源代码可以看出@Service和@Component没啥本质区别，官方文档也说了This annotation serves as a specialization of \{@link Component @Component\},

*  allowing for implementation classes to be autodetected through classpath scanning. 也就是@Service是一种具体的@Component，使得被注解类能通过classpath扫描被自动检测。

[Link 1]: https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#beans-java-bean-annotation
[Link 2]: https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#beans-java-basic-concepts
[Autowired]: https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#beans-autowired-annotation