Spring: @Component versus @Bean

java spring annotations autowired
user1396576 picture user1396576 · May 15, 2012 · Viewed 272.9k times · Source

I understand that @Component annotation was introduced in spring 2.5 in order to get rid of xml bean definition by using classpath scanning.

@Bean was introduced in spring 3.0 and can be used with @Configuration in order to fully get rid of xml file and use java config instead.

Would it have been possible to re-use the @Component annotation instead of introducing @Bean annotation? My understanding is that the final goal is to create beans in both cases.

Answer

skaffman picture skaffman · May 15, 2012

@Component and @Bean do two quite different things, and shouldn't be confused.

@Component (and @Service and @Repository) are used to auto-detect and auto-configure beans using classpath scanning. There's an implicit one-to-one mapping between the annotated class and the bean (i.e. one bean per class). Control of wiring is quite limited with this approach, since it's purely declarative.

@Bean is used to explicitly declare a single bean, rather than letting Spring do it automatically as above. It decouples the declaration of the bean from the class definition, and lets you create and configure beans exactly how you choose.

To answer your question...

would it have been possible to re-use the @Component annotation instead of introducing @Bean annotation?

Sure, probably; but they chose not to, since the two are quite different. Spring's already confusing enough without muddying the waters further.

Related questions

@Autowired - No qualifying bean of type found for dependency

I've started my project by creating entities, services and JUnit tests for services using Spring and Hibernate. All of this works great. Then I've added spring-mvc to make this web application using many different step-by-step tutorials, but when I'm trying …

Read More
@Resource vs @Autowired

Which annotation, @Resource (jsr250) or @Autowired (Spring-specific) should I use in DI? I have successfully used both in the past, @Resource(name="blah") and @Autowired @Qualifier("blah") My instinct is to stick with the @Resource tag since it's been ratified …

Read More
intellij incorrectly saying no beans of type found for autowired repository

I have created a simple unit test but IntelliJ is incorrectly highlighting it red. marking it as an error No beans? As you can see below it passes the test? So it must be Autowired?

Read More