@SpringBootApplication
public class HelloApplication {
    public static void main(String[] args) {
        SpringApplication.run(HelloApplication.class, args);
    }
}
@SpringBootApplication 开启组件扫描和自动配置
SpringApplication.run  启动引导应用程序

@EnableAutoConfiguration

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

AutoConfigurationImportSelector

@Import 导入类注册到容器中

public String[] selectImports(AnnotationMetadata annotationMetadata)
把所有符合条件的@Configuration配置都加载到容器中

该方法会在容器启动过程中执行
AbstractApplicationContext.refresh()


META-INF/spring.factories

org/springframework/boot/spring-boot-autoconfigure/2.0.0.RELEASE/spring-boot-autoconfigure-2.0.0.RELEASE.jar!/META-INF/spring.factories

# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\
org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\
org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\
org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\
org.springframework.boot.autoconfigure.cloud.CloudAutoConfiguration,\
org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\
org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,\
...


DataSourceAutoConfiguration


@Configuration
@ConditionalOnClass({ DataSource.class, EmbeddedDatabaseType.class })
@EnableConfigurationProperties(DataSourceProperties.class)
@Import({ DataSourcePoolMetadataProvidersConfiguration.class,
        DataSourceInitializationConfiguration.class })
public class DataSourceAutoConfiguration {

@ConfigurationProperties(prefix = "spring.datasource")
public class DataSourceProperties implements BeanClassLoaderAware, InitializingBean {

使用 @EnableConfigurationProperties ， DataSourceProperties 不需要 组件注解

 

 springboot自动配置原理和实例