@Target(ElementType.TYPE)//表示@SpringBootApplication的使用位置，表示用在類上
//1.CONSTRUCTOR:用于描述構(gòu)造器
//2.FIELD:用于描述域
//3.LOCAL_VARIABLE:用于描述局部變量
//4.METHOD:用于描述方法
//5.PACKAGE:用于描述包
//6.PARAMETER:用于描述參數(shù)
//7.TYPE:用于描述類、接口(包括注解類型) 或enum聲明
@Retention(RetentionPolicy.RUNTIME)//表示@SpringBootApplication的存在階段。
//1.RetentionPolicy.SOURCE —— 這種類型的Annotations只在源代碼級(jí)別保留,編譯時(shí)就會(huì)被忽略
//2.RetentionPolicy.CLASS —— 這種類型的Annotations編譯時(shí)被保留,在class文件中存在,但JVM將 會(huì)忽略
//3.RetentionPolicy.RUNTIME —— 這種類型的Annotations將被JVM保留,所以他們能在運(yùn)行時(shí)被JVM或其他使用反射機(jī)制的代碼所讀取和使用.
@Documented// “文檔” 注解表明這個(gè)注解應(yīng)該被 javadoc工具記錄
@Inherited//“繼承” 修飾@SpringBootApplication后，那么@SpringBootApplication用在哪個(gè)類上，且該類有子類的話，子類是可以繼承父類中的@SpringBootApplication
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = {
		@Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
		@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })

@Configuration
public @interface SpringBootConfiguration {...}

@Component
public @interface Configuration {...}

@Configuration
public class Configuration {
    // 任何標(biāo)志了@Bean的方法，其返回值將作為一個(gè)bean注冊(cè)到Spring的IOC容器中
    // 方法名默認(rèn)成為該bean定義的id
    @Bean
    public UserBean user() {
        return new UserBean();
    }
}

@AutoConfigurationPackage
@Import(EnableAutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {...}

// 從配置文件"META-INF/spring-autoconfigure-metadata.properties"中加載 AutoConfigurationMetadata
AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
    .loadMetadata(this.beanClassLoader);
//從注解中加載exclude和excludeName
AnnotationAttributes attributes = getAttributes(annotationMetadata);
//從所有jar包下的/META-INF/spring.factories的文件中獲取到候選的自動(dòng)配置類
List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);//重中之重
configurations = removeDuplicates(configurations);
configurations = sort(configurations, autoConfigurationMetadata);
Set<String> exclusions = getExclusions(annotationMetadata, attributes);
checkExcludedClasses(configurations, exclusions);
configurations.removeAll(exclusions);
configurations = filter(configurations, autoConfigurationMetadata);
fireAutoConfigurationImportEvents(configurations, exclusions);
return configurations.toArray(new String[configurations.size()]);

@Import(AutoConfigurationPackages.Registrar.class)
public @interface AutoConfigurationPackage {}

public static void register(BeanDefinitionRegistry registry, String... packageNames) {
		if (registry.containsBeanDefinition(BEAN)) {
			BeanDefinition beanDefinition = registry.getBeanDefinition(BEAN);
			ConstructorArgumentValues constructorArguments = beanDefinition
					.getConstructorArgumentValues();
			constructorArguments.addIndexedArgumentValue(0,
					addBasePackages(constructorArguments, packageNames));
		}
		else {
			GenericBeanDefinition beanDefinition = new GenericBeanDefinition();
			beanDefinition.setBeanClass(BasePackages.class);
			beanDefinition.getConstructorArgumentValues().addIndexedArgumentValue(0,
					packageNames);
			beanDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
            //ioc
			registry.registerBeanDefinition(BEAN, beanDefinition);
		}
	}

// Cannot modify startup-time collection elements anymore (for stable iteration)
//無法再修改啟動(dòng)時(shí)集合元素（用于穩(wěn)定的迭代）
synchronized (this.beanDefinitionMap) {
this.beanDefinitionMap.put(beanName, beanDefinition);
    。。。。。
}

@ComponentScan(excludeFilters = {
      @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
      @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })