自动配置原理

@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 {

springboot启动时加载主配置类，开启了自动配置功能

1. SpringBoot启动的时候加载主配置类，开启了自动配置功能@EnableAutoConfiguration
2. @EnableAutoConfiguration Import的AutoConfigurationImportSelector中代码最终调用SpringFactoriesLoader.loadSpringFactories扫描了Jar包的META-INF/spring.factories文件加载了大量的XXAutoConfiguration类
3. AutoConfiguration类配合Conditonal注解与ConfigurationProperties配置类在特定条件下自动装配我们需要的Bean到IOC容器中。