1主要通过ConfigurationClassParser类的doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)方法来扫描被ComponentScan注解的类。
2 此方法在spring容器的切入点为ConfigurationClassPostProcessor类，此类实现了接口BeanFactoryPostProcessor、BeanDefinitionRegistryPostProcessor，所以在spring启动时，会调用该类来插入配置扫描制定包下面的类，生成BeanDefinition。
3 真正处理扫描类为org.springframework.context.annotation.ClassPathBeanDefinitionScanner，该类的核心方法是：protected Set<BeanDefinitionHolder> doScan(String... basePackages)，
该方法把扫描制定包到的BeanDefinition，然后注入到 BeanDefinitionRegistry中
/**
* Perform a scan within the specified base packages,
* returning the registered bean definitions.
* <p>This method does <i>not</i> register an annotation config processor
* but rather leaves this up to the caller.
* @param basePackages the packages to check for annotated classes
* @return set of beans registered if any for tooling registration purposes (never {@code null})
*/
protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
Assert.notEmpty(basePackages, "At least one base package must be specified");
Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>();
for (String basePackage : basePackages) {
Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
for (BeanDefinition candidate : candidates) {
ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
candidate.setScope(scopeMetadata.getScopeName());
String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
if (candidate instanceof AbstractBeanDefinition) {
postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
}
if (candidate instanceof AnnotatedBeanDefinition) {
AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
}
if (checkCandidate(beanName, candidate)) {
BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
definitionHolder =
AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
beanDefinitions.add(definitionHolder);
registerBeanDefinition(definitionHolder, this.registry);
}
}
}
return beanDefinitions;
}