Spring Boot 自动包规则原理

https://www.bilibili.com/video/BV19K4y1L7MT/?p=13

引导加载的自动配置类

@SpringBootApplication

……
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
		@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {

@SpringBootConfiguration

@Configuration
public @interface SpringBootConfiguration {

@Configuration

代表当前是一个配置类，使用 @SpringBootApplication 的类也会是 Spring Boot 中的一个配置类

@ComponentScan

包扫描注解，指定扫描哪些包；

@EnableAutoConfiguration

……
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
……

@AutoConfigurationPackage

@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(AutoConfigurationPackages.Registrar.class) //给容器中导入一个组件
public @interface AutoConfigurationPackage {

比较关键的是 @Import(AutoConfigurationPackages.Registrar.class) 中导入的 AutoConfigurationPackages.Registrar

AutoConfigurationPackages.java

……	
	static class Registrar implements ImportBeanDefinitionRegistrar, DeterminableImports {

		@Override
		public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
			register(registry, new PackageImports(metadata).getPackageNames().toArray(new String[0]));
		}

		@Override
		public Set<Object> determineImports(AnnotationMetadata metadata) {
			return Collections.singleton(new PackageImports(metadata));
		}

	}
……

利用 Registrar 向容器中导入一系列组件，AnnotationMetadata metadata 传入的是 @SpringBootApplication 注解标注类的注解元信息，

然后经由 new PackageImport(metadata).getPackageName() 得到 @SpringBootApplication 注解标注类的包名（比如：io.github.jihch）,

最终目的是将指定一个包下（@SpringBootApplication 注解标注类的包）的所有组件导入进来，

这就解释了为什么默认是导入 @SpringBootApplication 注解标注类的包下的所有组件

https://www.bilibili.com/video/BV19K4y1L7MT?p=14

@Import(AutoConfigurationImportSelector.class)

AutoConfigurationImportSelector.java

……	
        @Override
	public String[] selectImports(AnnotationMetadata annotationMetadata) {
		if (!isEnabled(annotationMetadata)) {
			return NO_IMPORTS;
		}
		AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(annotationMetadata);
		return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
	}
……