1. @Bean:
1.1 定義
從定義可以看出，@Bean只能用於注解方法和注解的定義。
@Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
1.2 spring文檔中對 @Bean的說明
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：會實例化、配置並初始化一個新的對象，這個對象會由spring IoC 容器管理。
實例：
@Configuration
public class AppConfig {
@Bean
public MyService myService() {
return new MyServiceImpl();
}
}
相當於在 XML 文件中配置
<beans>
<bean id="myService" class="com.acme.services.MyServiceImpl"/>
</beans>
1.3 生成對象的名字：默認情況下用@Bean注解的方法名作為對象的名字。但是可以用 name屬性定義對象的名字，而且還可以使用name為對象起多個名字。
@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不同之處
（1）This method of declaring inter-bean dependencies only works when the @Bean method is declared within a @Configurationclass. You cannot declare inter-bean dependencies using plain @Component classes.
在 @Component 注解的類中不能定義 類內依賴的@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 定義
從定義看，用於注解類、接口、枚舉、注解的定義。
@Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME)
2.2 spring 文檔說明
@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用於類，表明這個類是beans定義的源。