SpringBoot自动装配原理详解

public class AutoConfigurationImportSelector implements DeferredImportSelector, BeanClassLoaderAware,
		ResourceLoaderAware, BeanFactoryAware, EnvironmentAware, Ordered {


	@Override
	public String[] selectImports(AnnotationMetadata annotationMetadata) {
		if (!isEnabled(annotationMetadata)) {
			return NO_IMPORTS;
		}
    // 获取自动配置的实体
		AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(annotationMetadata);
		return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
	}

  // 具体用来加载自动配置类得方法
	protected AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) {
		if (!isEnabled(annotationMetadata)) {
			return EMPTY_ENTRY;
		}
		AnnotationAttributes attributes = getAttributes(annotationMetadata);
    // 获取候选的配置类，即使后宫佳丽三千，也是要筛选的
		List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);
    // 根据情况，自动配置需要的配置类和不需要的配置了
		configurations = removeDuplicates(configurations);
		Set<String> exclusions = getExclusions(annotationMetadata, attributes);
		checkExcludedClasses(configurations, );
		configurations.removeAll(exclusions);
		configurations = getConfigurationClassFilter().filter(configurations);
		fireAutoConfigurationImportEvents(configurations, exclusions);
    // 返回最终需要的配置
		return new AutoConfigurationEntry(configurations, exclusions);
	}
}

	protected static class AutoConfigurationEntry {
    // 用来存储需要的配置项
		private final List<String> configurations;
    // 用来存储排除的配置项
		private final Set<String> exclusions;

		private AutoConfigurationEntry() {
			this.configurations = Collections.emptyList();
			this.exclusions = Collections.emptySet();
		}
  }

	protected Class<?> getSpringFactoriesLoaderFactoryClass() {
    // 返回的是EnableAutoConfiguration字节码对象
		return EnableAutoConfiguration.class;
	}

protected ClassLoader getBeanClassLoader() {
		return this.beanClassLoader;
	}

	public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) {
		ClassLoader classLoaderToUse = classLoader;
		if (classLoaderToUse == null) {
			classLoaderToUse = SpringFactoriesLoader.class.getClassLoader();
		}
    // 获取的EnableAutoConfiguration.class的权限定名
    //org.springframework.boot.autoconfigure.EnableAutoConfiguration
		String factoryTypeName = factoryType.getName();
		return loadSpringFactories(classLoaderToUse).getOrDefault(factoryTypeName, Collections.emptyList());
	}

	private static Map<String, List<String>> loadSpringFactories(ClassLoader classLoader) {
    // 缓存加载的配置类
		Map<String, List<String>> result = cache.get(classLoader);
		if (result != null) {
			return result;
		}
    
		result = new HashMap<>();
		try {
      // 去资源目录下找
			Enumeration<URL> urls = classLoader.getResources(FACTORIES_RESOURCE_LOCATION);
			while (urls.hasMoreElements()) {
				URL url = urls.nextElement();
				UrlResource resource = new UrlResource(url);
				Properties properties = PropertiesLoaderUtils.loadProperties(resource);
				for (Map.Entry<?, ?> entry : properties.entrySet()) {
					String factoryTypeName = ((String) entry.getKey()).trim();
					String[] factoryImplementationNames =
							StringUtils.commaDelimitedListToStringArray((String) entry.getValue());
					for (String factoryImplementationName : factoryImplementationNames) {
						result.computeIfAbsent(factoryTypeName, key -> new ArrayList<>())
								.add(factoryImplementationName.trim());
					}
				}
			}

			// Replace all lists with unmodifiable lists containing unique elements
			result.replaceAll((factoryType, implementations) -> implementations.stream().distinct()
					.collect(Collectors.collectingAndThen(Collectors.toList(), Collections::unmodifiableList)));
      // 加载完成放到缓存中
			cache.put(classLoader, result);
		}
		catch (IOException ex) {
			throw new IllegalArgumentException("Unable to load factories from location [" +
					FACTORIES_RESOURCE_LOCATION + "]", ex);
		}
    // 返回加载到的配置类
		return result;
	}