Spring Bean的包扫描的实现方法

protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
		Assert.notEmpty(basePackages, "At least one base package must be specified");
		Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>();
		// 可以指定多个basePackage,这里就对每个都处理
		for (String basePackage : basePackages) {
		  // 这个方法是真正的查找候选Bean的地方
			Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
			// 对于每个查找出的候选Bean，进行处理
			for (BeanDefinition candidate : candidates) {
			  // 解析@Scope的元数据
				ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
				candidate.setScope(scopeMetadata.getScopeName());
				// 为候选的Bean生成一个名称
				String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
				// 应用后置处理器
				if (candidate instanceof AbstractBeanDefinition) {
					postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
				}
				// 
				// 处理一些其它通用的注解的元数据
				if (candidate instanceof AnnotatedBeanDefinition) {
					AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
				}
				// 校验通过后，注册到 BeanFactory
				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;
	}

SimpleMetadataReader(Resource resource, @Nullable ClassLoader classLoader) throws IOException {
    // 通过流读取资源的内容，现在这个资源可以认为是我们的类
		InputStream is = new BufferedInputStream(resource.getInputStream());
		ClassReader classReader;
		try {
		  // 这个Reader的构造器中就将流读取完毕了
			classReader = new ClassReader(is);
		}
		catch (IllegalArgumentException ex) {
		  // 通过这个异常的信息，可以推测出，其实这里是通过ASM读取Class文件的定义了
			throw new NestedIOException("ASM ClassReader failed to parse class file - " +
					"probably due to a new Java class file version that isn't supported yet: " + resource, ex);
		}
		finally {
			is.close();
		}

    // 这里根据命名可以推测是访问者模式来暴露注解的元数据
		AnnotationMetadataReadingVisitor visitor = new AnnotationMetadataReadingVisitor(classLoader);

		// 这个accpect方法也是访问者模式中的典型方法，在这里面，是数据的解析逻辑
		classReader.accept(visitor, ClassReader.SKIP_DEBUG);

		this.annotationMetadata = visitor;
		// (since AnnotationMetadataReadingVisitor extends ClassMetadataReadingVisitor)
		this.classMetadata = visitor;
		this.resource = resource;
	}