SpringBoot-自动配置1

最新推荐文章于 2024-09-10 20:24:34 发布

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本文详细解析了SpringBoot自动配置的实现原理，介绍了如何通过扫描META-INF/spring.factories文件来加载自动配置列表，并深入探讨了@SpringBootApplication和@EnableAutoConfiguration注解的作用。

1、想了解自动配置原理的建议先了解注解原理，了解几个基本的元注解：https://www.cnblogs.com/peida/archive/2013/04/24/3036689.html

SpringBoot实现原理：通过扫描META-INF/spring.factories文件，该文件记录了springBoot实现的自动配置列表，通过加载这个列表实现所有的自动配置

2、SpringBootApplication注解：一个组合注解

@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 {

	@AliasFor(annotation = EnableAutoConfiguration.class, attribute = "exclude")
	Class<?>[] exclude() default {};

	@AliasFor(annotation = EnableAutoConfiguration.class, attribute = "excludeName")
	String[] excludeName() default {};

	@AliasFor(annotation = ComponentScan.class, attribute = "basePackages")
	String[] scanBasePackages() default {};
	@AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses")
	Class<?>[] scanBasePackageClasses() default {};

}

核心功能由@EnableAutoConfiguration实现

@EnableAutoConfiguration注解：

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

	String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";

	Class<?>[] exclude() default {};

	String[] excludeName() default {};

}

@EnableAutoConfiguration注解通过@Import注解引入EnableAutoConfigtionImportSelectot.class实现主要功能

EnableAutoConfigtionImportSelectot.class继承AutoConfigurationImportSelector

AutoConfigurationImportSelector类通过getCandidateConfigurations加载META-INF/spring.factories信息，获取需要自动配置的类

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;
	}