前言

在使用SpringBoot使用过程中
@RestController、@Service、@Repository这几个注解类上都标有@Component注解
启动类上标有的@SpringBootApplication注解类上有个@ComponentScan注解。那么@ComponentScan如何把相关的对象注册到BeanFactory的？

找到处理ComponentScan注解的代码

从启动类找到refresh(context)

public static void main(String[] args) {
   SpringApplication.run(Application.class, args);
}

点击run进入

public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {
	return run(new Class<?>[] { primarySource }, args);
}

点击run进入

public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
	return new SpringApplication(primarySources).run(args);
}

点击run进入

public ConfigurableApplicationContext run(String... args) {
	...
	try {
		...
		refreshContext(context);
		...
	}
	catch (Throwable ex) {
		...
	}
	...
	return context;
}

找到refreshContext(context)点击进入

private void refreshContext(ConfigurableApplicationContext context) {
	if (this.registerShutdownHook) {
		shutdownHook.registerApplicationContext(context);
	}
	refresh(context);
}

点击进入，在找到接口实现

查看更多refresh(context)方法查看细读Spring Boot源码】重中之重refresh()

从refresh(context)找到处理ComponentScan注解的代码

refresh(context)进入后

@Override
public void refresh() throws BeansException, IllegalStateException {
	synchronized (this.startupShutdownMonitor) {
		...
		try {
			...
			// Invoke factory processors registered as beans in the context.
			invokeBeanFactoryPostProcessors(beanFactory);
			...
		}
		catch (BeansException ex) {
			...
		}
		finally {
			...
		}
	}
}

找到invokeBeanFactoryPostProcessors(beanFactory);进入

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
	// 进入
	PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());	
	...
}

进入PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors，代码很多任意找到一个invokeBeanDefinitionRegistryPostProcessors()进入

private static void invokeBeanDefinitionRegistryPostProcessors(
		Collection<? extends BeanDefinitionRegistryPostProcessor> postProcessors, BeanDefinitionRegistry registry, ApplicationStartup applicationStartup) {

	for (BeanDefinitionRegistryPostProcessor postProcessor : postProcessors) {
		StartupStep postProcessBeanDefRegistry = applicationStartup.start("spring.context.beandef-registry.post-process")
				.tag("postProcessor", postProcessor::toString);
		postProcessor.postProcessBeanDefinitionRegistry(registry);
		postProcessBeanDefRegistry.end();
	}
}

发现是一个BeanFactoryPostProcessor接口类的回调处理

找到进入ConfigurationClassPostProcessor实现类找到postProcessBeanFactory()方法