springboot自动状态原理

主要涉及的注解

1. SpringBootApplication
2. EnableAutoConfiguration
3. Import

传递关系

	SpringBootApplication->EnableAutoConfiguration->Import

主要涉及的类

1. AutoConfigurationImportSelector

import注解作用

@Import(AutoConfigurationImportSelector.class) 会将这个class到spring容器中

重要的方法

	//获取需要加载的class
   public String[] selectImports(AnnotationMetadata annotationMetadata) {
   	if (!isEnabled(annotationMetadata)) {
   		return NO_IMPORTS;
   	}
   	AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(annotationMetadata);
   	return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
   }

   	/**
    * Return the {@link AutoConfigurationEntry} based on the {@link AnnotationMetadata}
    * of the importing {@link Configuration @Configuration} class.
    * @param annotationMetadata the annotation metadata of the configuration class
    * @return the auto-configurations that should be imported
    */
   protected AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) {
   	if (!isEnabled(annotationMetadata)) {
   		return EMPTY_ENTRY;
   	}
   	AnnotationAttributes attributes = getAttributes(annotationMetadata);
   	List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);
   	configurations = removeDuplicates(configurations);
   	Set<String> exclusions = getExclusions(annotationMetadata, attributes);
   	checkExcludedClasses(configurations, exclusions);
   	configurations.removeAll(exclusions);
   	configurations = getConfigurationClassFilter().filter(configurations);
   	fireAutoConfigurationImportEvents(configurations, exclusions);
   	return new AutoConfigurationEntry(configurations, exclusions);
   }

   /**
    * Return the auto-configuration class names that should be considered. By default
    * this method will load candidates using {@link ImportCandidates} with
    * {@link #getSpringFactoriesLoaderFactoryClass()}. For backward compatible reasons it
    * will also consider {@link SpringFactoriesLoader} with
    * {@link #getSpringFactoriesLoaderFactoryClass()}.
    * @param metadata the source metadata
    * @param attributes the {@link #getAttributes(AnnotationMetadata) annotation
    * attributes}
    * @return a list of candidate configurations
    */
   protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
   	List<String> configurations = new ArrayList<>(
   			//FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";  
   			//EnableAutoConfiguration.class 加载的上面位置文件里的class
   			SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader()));
   	ImportCandidates.load(AutoConfiguration.class, getBeanClassLoader()).forEach(configurations::add);
   	Assert.notEmpty(configurations,
   			"No auto configuration classes found in META-INF/spring.factories nor in META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports. If you "
   					+ "are using a custom packaging, make sure that file is correct.");
   	return configurations;
   }