總結
@Bean：表示一個方法實例化、配置或者初始化一個Spring IoC容器管理的新對象。
@Component: 自動被comonent掃描。 表示被注解的類會自動被component掃描
@Repository: 用於持久層，主要是數據庫存儲庫。
@Service: 表示被注解的類是位於業務層的業務component。
@Controller:表明被注解的類是控制component，主要用於展現層 。
@Bean與@Component區別
@Component是 spring 2.5引入的，為了擺脫通過classpath掃描根據xml方式定義的bean的方式.
@Bean是spring 3.0 引入的，和 @Configuration一起工作，為了擺脫原先的xml和java config方式。
Spring管理Bean方式有兩種，一種是注冊Bean，一種裝配Bean。
可以通過三種方式實現bean管理，一使用自動配置的方式、二使用JavaConfig的方式、三使用XML配置的方式。
@Compent 作用就相當於 XML配置
@Component
@Data
public class User{
private String name = "tom";
}
@Bean 需要在配置類中使用，即類上需要加上@Component或者@Configuration注解， 通常加上@Configuration。 @Bean的用法在這里。
@Configuration
public class AppConfig {
@Bean
public TransferServiceImpl transferService() {
return new TransferServiceImpl();
}
}
兩者都可以通過@Autowired裝配
@Autowired
private TransferService transferService;
@Component與@Service區別
目前基本沒有區別。
參看源代碼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 "";
}
從源代碼可以看出@Service和@Component沒啥本質區別，官方文檔也說了This annotation serves as a specialization of {@link Component @Component},
allowing for implementation classes to be autodetected through classpath scanning. 也就是@Service是一種具體的@Component，使得被注解類能通過classpath掃描被自動檢測。