自定义spring boot starter三部曲之三：源码分析spring.factories加载过程

org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.bolingcavalry.customizeservicestarter.CustomizeConfiguration

private void processDeferredImportSelectors() {
		//这里就是Configuration注解中的Import注解的值，
		//例如EnableAutoConfiguration注解的源码中，Import注解的值是EnableAutoConfigurationImportSelector.class
		List<DeferredImportSelectorHolder> deferredImports = this.deferredImportSelectors;
		this.deferredImportSelectors = null;
		Collections.sort(deferredImports, DEFERRED_IMPORT_COMPARATOR);

		for (DeferredImportSelectorHolder deferredImport : deferredImports) {
			ConfigurationClass configClass = deferredImport.getConfigurationClass();
			try {
				//以EnableAutoConfiguration注解为例，其Import注解的值为EnableAutoConfigurationImportSelector.class，
				//那么此处就是在调用EnableAutoConfigurationImportSelector的selectImports方法，返回了一个字符串数组
				String[] imports = deferredImport.getImportSelector().selectImports(configClass.getMetadata());
				//字符串数组中的每个字符串都代表一个类，此处做实例化
				processImports(configClass, asSourceClass(configClass), asSourceClasses(imports), false);
			}
			catch (BeanDefinitionStoreException ex) {
				throw ex;
			}
			catch (Throwable ex) {
				throw new BeanDefinitionStoreException(
						"Failed to process import candidates for configuration class [" +
						configClass.getMetadata().getClassName() + "]", ex);
			}
		}
	}

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = {
		@Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
		@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {
	......

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(EnableAutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
	......

/**
 * {@link DeferredImportSelector} to handle {@link EnableAutoConfiguration
 * auto-configuration}. This class can also be subclassed if a custom variant of
 * {@link EnableAutoConfiguration @EnableAutoConfiguration}. is needed.
 *
 * @deprecated as of 1.5 in favor of {@link AutoConfigurationImportSelector}
 * @author Phillip Webb
 * @author Andy Wilkinson
 * @author Stephane Nicoll
 * @author Madhura Bhave
 * @since 1.3.0
 * @see EnableAutoConfiguration
 */
@Deprecated
public class EnableAutoConfigurationImportSelector
		extends AutoConfigurationImportSelector {

	@Override
	protected boolean isEnabled(AnnotationMetadata metadata) {
		if (getClass().equals(EnableAutoConfigurationImportSelector.class)) {
			return getEnvironment().getProperty(
					EnableAutoConfiguration.ENABLED_OVERRIDE_PROPERTY, Boolean.class,
					true);
		}
		return true;
	}

}

@Override
	public String[] selectImports(AnnotationMetadata annotationMetadata) {
		if (!isEnabled(annotationMetadata)) {
			return NO_IMPORTS;
		}
		try {
		    //将所有spring-autoconfigure-metadata.properties文件中的键值对保存在autoConfigurationMetadata中
			AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
					.loadMetadata(this.beanClassLoader);
			AnnotationAttributes attributes = getAttributes(annotationMetadata);
			//取得所有配置类的名称
			List<String> configurations = getCandidateConfigurations(annotationMetadata,
					attributes);
			configurations = removeDuplicates(configurations);
			configurations = sort(configurations, autoConfigurationMetadata);
			Set<String> exclusions = getExclusions(annotationMetadata, attributes);
			checkExcludedClasses(configurations, exclusions);
			configurations.removeAll(exclusions);
			configurations = filter(configurations, autoConfigurationMetadata);
			fireAutoConfigurationImportEvents(configurations, exclusions);
			return configurations.toArray(new String[configurations.size()]);
		}
		catch (IOException ex) {
			throw new IllegalStateException(ex);
		}
	}

protected List<String> getCandidateConfigurations(AnnotationMetadata metadata,
			AnnotationAttributes attributes) {
		List<String> configurations = SpringFactoriesLoader.loadFactoryNames(
				getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader());
		Assert.notEmpty(configurations,
				"No auto configuration classes found in META-INF/spring.factories. If you "
						+ "are using a custom packaging, make sure that file is correct.");
		return configurations;
	}

protected Class<?> getSpringFactoriesLoaderFactoryClass() {
		return EnableAutoConfiguration.class;
	}