深入浅出org.springframework.context.annotation.Import、ImportSelector、ImportBeanDefinitionRegistrar

Import

https://docs.spring.io/spring-framework/docs/current/reference/html/core.html#beans

源码注释

Indicates one or more component classes to import — typically @Configuration classes.

标记要导入的一个或者多个组件类，尤其是被 @Configuration 标记的类。

---

Provides functionality equivalent to the element in Spring XML. Allows for importing @Configuration classes, ImportSelector and ImportBeanDefinitionRegistrar implementations, as well as regular component classes (as of 4.2; analogous to AnnotationConfigApplicationContext.register).

和 Spring XML中的 import 标签相同的功能。允许导入@Configuration 类，ImportSelector 和ImportBeanDefinitionRegistrar 的实现类，以及常规组件类（）

AnnotationConfigApplicationContext.register源码

	@Override
	public void register(Class<?>... componentClasses) {
   
		Assert.notEmpty(componentClasses, "At least one component class must be specified");
		StartupStep registerComponentClass = this.getApplicationStartup().start("spring.context.component-classes.register")
				.tag("classes", () -> Arrays.toString(componentClasses));
		this.reader.register(componentClasses);
		registerComponentClass.end();
	}

If XML or other non-@Configuration bean definition resources need to be imported, use the @ImportResource annotation instead.

如果XML或者其他非@Configuration bean definition 资源需要导入，使用@ImportResource注解替代。

源码

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Import {
   	
	Class<?>[] value();
}

只有一个参数接收Class数组。

常见用法

DataSourceAutoConfiguration

	@Import({
    DataSourcePoolMetadataProvidersConfiguration.class,
	 DataSourceInitializationConfiguration.class })

	@Import(EmbeddedDataSourceConfiguration.class)
	
	@Import({
    DataSourceConfiguration.Hikari.class, DataSourceConfiguration.Tomcat.class,
			DataSourceConfiguration.Dbcp2.class, DataSourceConfiguration.OracleUcp.class,
			DataSourceConfiguration.Generic.class, DataSourceJmxConfiguration.class })

问题一：Import数组的顺序性

在DefaultListableBeanFactory类中preInstantiateSingletons方法中的beanNames列表中