给容器中注册组件的方式
- 包扫描+标注注解（@Controller/@Service/@Repository/@Component）一般用于自己写的类
@Configuration+@Bean，一般用于导入的第三方包里面的组件@Import，一般用于封装公共组件，提供jar包
/**
* Indicates one or more {@link Configuration @Configuration} classes to import.
*
* <p>Provides functionality equivalent to the {@code <import/>} element in Spring XML.
* Allows for importing {@code @Configuration} classes, {@link ImportSelector} and
* {@link ImportBeanDefinitionRegistrar} implementations, as well as regular component
* classes (as of 4.2; analogous to {@link AnnotationConfigApplicationContext#register}).
*
* <p>{@code @Bean} definitions declared in imported {@code @Configuration} classes should be
* accessed by using {@link org.springframework.beans.factory.annotation.Autowired @Autowired}
* injection. Either the bean itself can be autowired, or the configuration class instance
* declaring the bean can be autowired. The latter approach allows for explicit, IDE-friendly
* navigation between {@code @Configuration} class methods.
*
* <p>May be declared at the class level or as a meta-annotation.
*
* <p>If XML or other non-{@code @Configuration} bean definition resources need to be
* imported, use the {@link ImportResource @ImportResource} annotation instead.
*
* @author Chris Beams
* @author Juergen Hoeller
* @since 3.0
* @see Configuration
* @see ImportSelector
* @see ImportResource
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Import {
/**
* {@link Configuration}, {@link ImportSelector}, {@link ImportBeanDefinitionRegistrar}
* or regular component classes to import.
*/
Class<?>[] value();
}
@Import(组件)；容器中就会自动注册这个组件，id默认是全类名，如果导入的是@Configuration，没那么其类中的@Bean也会全部被导入@Import(ImportSelector或者DeferredImportSelector):返回需要导入的组件的全类名数组；
/**
* Interface to be implemented by types that determine which @{@link Configuration}
* class(es) should be imported based on a given selection criteria, usually one or more
* annotation attributes.
*
* <p>An {@link ImportSelector} may implement any of the following
* {@link org.springframework.beans.factory.Aware Aware} interfaces, and their respective
* methods will be called prior to {@link #selectImports}:
* <ul>
* <li>{@link org.springframework.context.EnvironmentAware EnvironmentAware}</li>
* <li>{@link org.springframework.beans.factory.BeanFactoryAware BeanFactoryAware}</li>
* <li>{@link org.springframework.beans.factory.BeanClassLoaderAware BeanClassLoaderAware}</li>
* <li>{@link org.springframework.context.ResourceLoaderAware ResourceLoaderAware}</li>
* </ul>
*
* <p>ImportSelectors are usually processed in the same way as regular {@code @Import}
* annotations, however, it is also possible to defer selection of imports until all
* {@code @Configuration} classes have been processed (see {@link DeferredImportSelector}
* for details).
*
* @author Chris Beams
* @since 3.1
* @see DeferredImportSelector
* @see Import
* @see ImportBeanDefinitionRegistrar
* @see Configuration
*/
public interface ImportSelector {
/**
* Select and return the names of which class(es) should be imported based on
* the {@link AnnotationMetadata} of the importing @{@link Configuration} class.
*/
String[] selectImports(AnnotationMetadata importingClassMetadata);
}
AnnotationMetadata可以获取到标注这个注解的类的相关信息，返回值不可为null，是导入类的全类名。
ImportSelector的实现类可以实现EnvironmentAware、BeanFactoryAware、BeanClassLoaderAware、ResourceLoaderAware接口获取相关的环境信息。
@Import(BeanDefinitionRegistrar):手动注册bean到容器中
/**
* Interface to be implemented by types that register additional bean definitions when
* processing @{@link Configuration} classes. Useful when operating at the bean definition
* level (as opposed to {@code @Bean} method/instance level) is desired or necessary.
*
* <p>Along with {@code @Configuration} and {@link ImportSelector}, classes of this type
* may be provided to the @{@link Import} annotation (or may also be returned from an
* {@code ImportSelector}).
*
* <p>An {@link ImportBeanDefinitionRegistrar} may implement any of the following
* {@link org.springframework.beans.factory.Aware Aware} interfaces, and their respective
* methods will be called prior to {@link #registerBeanDefinitions}:
* <ul>
* <li>{@link org.springframework.context.EnvironmentAware EnvironmentAware}</li>
* <li>{@link org.springframework.beans.factory.BeanFactoryAware BeanFactoryAware}
* <li>{@link org.springframework.beans.factory.BeanClassLoaderAware BeanClassLoaderAware}
* <li>{@link org.springframework.context.ResourceLoaderAware ResourceLoaderAware}
* </ul>
*
* <p>See implementations and associated unit tests for usage examples.
*
* @author Chris Beams
* @since 3.1
* @see Import
* @see ImportSelector
* @see Configuration
*/
public interface ImportBeanDefinitionRegistrar {
/**
* Register bean definitions as necessary based on the given annotation metadata of
* the importing {@code @Configuration} class.
* <p>Note that {@link BeanDefinitionRegistryPostProcessor} types may <em>not</em> be
* registered here, due to lifecycle constraints related to {@code @Configuration}
* class processing.
* @param importingClassMetadata annotation metadata of the importing class
* @param registry current bean definition registry
*/
public void registerBeanDefinitions(
AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry);
}
AnnotationMetadata可以获取到标注这个注解的类的相关信息，通过BeanDefinitionRegistry手动注册组件。
ImportBeanDefinitionRegistrar的实现类可以实现EnvironmentAware、BeanFactoryAware、BeanClassLoaderAware、ResourceLoaderAware接口获取相关的环境信息。
5. 使用Spring提供的 FactoryBean，非常适合整合其他框架;
- 默认获取到的是工厂bean调用getObject创建的对象
- 要获取工厂Bean本身，我们需要给id前面加一个&
6. 直接注册一个Bean：SingletonBeanRegistry#registerSingleton
