//@SpringBootApplication 來標注一個主程序類
//說明這是一個Spring Boot應(yīng)用
@SpringBootApplication
public class SpringbootApplication {
   public static void main(String[] args) {
     //以為是啟動了一個方法，沒想到啟動了一個服務(wù)
      SpringApplication.run(SpringbootApplication.class, args);
   }
}

@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(
    excludeFilters = {@Filter(
    type = FilterType.CUSTOM,
    classes = {TypeExcludeFilter.class}
), @Filter(
    type = FilterType.CUSTOM,
    classes = {AutoConfigurationExcludeFilter.class}
)}
)
public @interface SpringBootApplication {
    // ......
}

//@SpringBootConfiguration注解內(nèi)部
//這里的 @Configuration，說明這是一個配置類 ，配置類就是對應(yīng)Spring的xml 配置文件；
@Configuration
public @interface SpringBootConfiguration {}
//里面的 @Component 這就說明，啟動類本身也是Spring中的一個組件而已，負責啟動應(yīng)用
@Component
public @interface Configuration {}

import java.lang.annotation. Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.context.annotation.Import;
@Target({ElementTypeTYPE})
@Retention(RetentionPolicy.RUNTIME)@Documented
@Inherited
@AutoconfigurationPackage
@Import( {AutoconfigurationImportselector.class})
public @interface EnableAutoconfiguration{
    string ENABLED_OVERRIDE_PROPERTY ="spring.boot.enableautoconfiguration" ;
    class<?>[]exclude() default {};
    string[ ] excludeName( ) default {};
}

//AutoConfigurationPackage的子注解
//Registrar.class 作用：將主啟動類的所在包及包下面所有子包里面的所有組件掃描到Spring容器 
@Import({Registrar.class})
public @interface AutoConfigurationPackage {
}

 protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
        List<String> configurations = SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass(), this.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;
    }