@Configuration 和 @Bean

1. @Bean:

1.1 定义

从定义可以看出,@Bean只能用于注解方法和注解的定义。


@Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)

1.2 spring文档中对 @Bean的说明

The @Bean annotation is used to indicate that a method instantiates, configures and initializes a new object to be managed by the Spring IoC container.

For those familiar with Spring’s <beans/> XML configuration the @Bean annotation plays the same role as the <bean/> element.

用@Bean注解的方法:会实例化、配置并初始化一个新的对象,这个对象会由spring IoC 容器管理。

实例:

@Configuration
public class AppConfig { @Bean
public MyService myService() {
return new MyServiceImpl();
} }

相当于在 XML 文件中配置

<beans>
<bean id="myService" class="com.acme.services.MyServiceImpl"/>
</beans>

1.3 生成对象的名字:默认情况下用@Bean注解的方法名作为对象的名字。但是可以用 name属性定义对象的名字,而且还可以使用name为对象起多个名字。

@Configuration
public class AppConfig { @Bean(name = "myFoo")
public Foo foo() {
return new Foo();
} }
@Configuration
public class AppConfig { @Bean(name = { "dataSource", "subsystemA-dataSource", "subsystemB-dataSource" })
public DataSource dataSource() {
// instantiate, configure and return DataSource bean...
} }

1.4 @Bean 一般和 @Component或者@Configuration 一起使用。

@Component和@Configuration不同之处

(1)This method of declaring inter-bean dependencies only works when the @Bean method is declared within a @Configuration class. You cannot declare inter-bean dependencies using plain @Component classes.

在 @Component 注解的类中不能定义 类内依赖的@Bean注解的方法。@Configuration可以。

@Configuration
public class AppConfig { @Bean
public Foo foo() {
return new Foo(bar());
} @Bean
public Bar bar() {
return new Bar();
} }

2. @Configuration:

2.1 定义

从定义看,用于注解类、接口、枚举、注解的定义。

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)

2.2 spring 文档说明

@Configuration is a class-level annotation indicating that an object is a source of bean definitions. @Configuration classes declare beans via public @Bean annotated methods.

@Configuration用于类,表明这个类是beans定义的源。

 
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