查看“Spring Boot 自动包规则原理”的源代码

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

=== 引导加载的自动配置类 ===

==== @SpringBootApplication ====
<syntaxhighlight lang="java">
……
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
		@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {
</syntaxhighlight>

===== @SpringBootConfiguration =====
<syntaxhighlight lang="java">
@Configuration
public @interface SpringBootConfiguration {
</syntaxhighlight>

====== @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 ====
<syntaxhighlight lang="java">
……
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
……
</syntaxhighlight>

===== @AutoConfigurationPackage =====
<syntaxhighlight lang="java">
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(AutoConfigurationPackages.Registrar.class) //给容器中导入一个组件
public @interface AutoConfigurationPackage {
</syntaxhighlight>比较关键的是 <code>@Import(AutoConfigurationPackages.Registrar.class)</code> 中导入的 AutoConfigurationPackages.Registrar

====== AutoConfigurationPackages.java ======
<syntaxhighlight lang="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));
		}

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

然后经由 <code>new PackageImport(metadata).getPackageName()</code> 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 ======
<syntaxhighlight lang="java">
……	
        @Override
	public String[] selectImports(AnnotationMetadata annotationMetadata) {
		if (!isEnabled(annotationMetadata)) {
			return NO_IMPORTS;
		}
		AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(annotationMetadata);
		return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
	}
……
	protected AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) {
		if (!isEnabled(annotationMetadata)) {
			return EMPTY_ENTRY;
		}
		AnnotationAttributes attributes = getAttributes(annotationMetadata);
		List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);
		configurations = removeDuplicates(configurations);
		Set<String> exclusions = getExclusions(annotationMetadata, attributes);
		checkExcludedClasses(configurations, exclusions);
		configurations.removeAll(exclusions);
		configurations = getConfigurationClassFilter().filter(configurations);
		fireAutoConfigurationImportEvents(configurations, exclusions);
		return new AutoConfigurationEntry(configurations, exclusions);
	}
……
</syntaxhighlight>利用 <code>getAutoConfigurationEntry(annotationMetadata)</code> 往容器中批量导入一些组件：
[[文件:利用 getAutoConfigurationEntry 导入组件.png|无|缩略图|1151x1151像素]]用 <code>List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);</code> 获取到所有需要导入到容器中的组件