1. @Bean:

1.1 定義

從定義可以看出，@Bean只能用于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(duì) @Bean的說(shuō)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(huì)實(shí)例化、配置并初始化一個(gè)新的對(duì)象，這個(gè)對(duì)象會(huì)由spring IoC 容器管理。

實(shí)例：

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

相當(dāng)于在 XML 文件中配置

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

1.3 生成對(duì)象的名字：默認(rèn)情況下用@Bean注解的方法名作為對(duì)象的名字。但是可以用 name屬性定義對(duì)象的名字，而且還可以使用name為對(duì)象起多個(gè)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(nèi)依賴的@Bean注解的方法。@Configuration可以。

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

2. @Configuration:

2.1 定義

從定義看，用于注解類、接口、枚舉、注解的定義。

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

?2.2 spring 文檔說(shuō)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用于類，表明這個(gè)類是beans定義的源。

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