EnableAutoConfiguration 注解 - 高级 - springboot - spring - java - 计算机学科

# @EnableAutoConfiguration 注解

@EnableAutoConfiguratioon 注解内部使用 @Import (AutoConfigurationImportSelector.class) 来加载配置类。

配置文件位置：META-INF/spring.factories，该配置文件中定义了大量的配置类，当 SpringBoot 应用启动时，会自动加载这些配置类，初始化 Bean

并不是所有的 Bean 都会被初始化，在配置类中使用 Condition 来加载满足条件的 Bean

点击进入 @SpringBootApplication 注解内部

里面有 EnableAutoConfiguration 点击进入查看

	@Target(ElementType.TYPE)
	@Retention(RetentionPolicy.RUNTIME)
	@Documented
	@Inherited
	@AutoConfigurationPackage
	// 导入了自动配置的 Selector
	@Import(AutoConfigurationImportSelector.class)
	public @interface EnableAutoConfiguration {

	/**
	* Environment property that can be used to override when auto-configuration is
	* enabled.
	*/
	String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";

	/**
	* Exclude specific auto-configuration classes such that they will never be applied.
	* @return the classes to exclude
	*/
	Class<?>[] exclude() default {};

	/**
	* Exclude specific auto-configuration class names such that they will never be
	* applied.
	* @return the class names to exclude
	* @since 1.3.0
	*/
	String[] excludeName() default {};

	}

在 AutoConfigurationImportSelector 中重写了 selectImports

	@Override
	// String [] 数组返回定义了很多需要被加载的类
	public String[] selectImports(AnnotationMetadata annotationMetadata) {
	if (!isEnabled(annotationMetadata)) {
	return NO_IMPORTS;
	} // 通过 getAutoConfigurationEntry 加载后返回 AutoConfigurationEntry 对象
	AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(annotationMetadata);
	// 将 autoConfigurationEntry 转换为字符串数组
	return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
	}

查看核心的源代码：

	protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
	// 通过 SpringFactoriesLoader 加载并返回 List 集合，这个 List 集合中就是所有需要加载的类
	List<String> configurations = new ArrayList<>(
	SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader()));
	ImportCandidates.load(AutoConfiguration.class, getBeanClassLoader()).forEach(configurations::add);
	// 如果上面 List 集合是空的则下面断言抛出错误信息
	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;
	}