@SpringBootApplication解析

注解中主要的三个注解

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

1、@SpringBootConfiguration

@Configuration。代表当前是一个配置类

2、@ComponentScan

指定扫描哪些，Spring注解；

3、@EnableAutoConfiguration

两个重要注解

@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {

1、@AutoConfigurationPackage

Registrar是把某一个包下的所有组件注册到容器中

利用Registrar给容器中导入一系列组件、将MainApplication所在包下的所有组件导入进来。

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

/**
 * {@link ImportBeanDefinitionRegistrar} to store the base package from the importing
 * configuration.
 *
 * 用于存储来自导入配置的基本包
 */
static class Registrar implements ImportBeanDefinitionRegistrar, DeterminableImports {

   @Override
   public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
      register(registry, new PackageImports(metadata).getPackageNames().toArray(new String[0]));
   }

   @Override
   public Set<Object> determineImports(AnnotationMetadata metadata) {
      return Collections.singleton(new PackageImports(metadata));
   }

}

2.@Import(AutoConfigurationImportSelector.class)

    返回要注册组件的集合
    @Override
    public String[] selectImports(AnnotationMetadata annotationMetadata) {
        if (!isEnabled(annotationMetadata)) {
            return NO_IMPORTS;
        }
        AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(annotationMetadata);
        return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
    }

   /**
     * Return the {@link AutoConfigurationEntry} based on the {@link AnnotationMetadata}
     * of the importing {@link Configuration @Configuration} class.
     * @param annotationMetadata the annotation metadata of the configuration class
     * @return the auto-configurations that should be imported
     */
    
    // 根据路径获取所有组件 根据条件筛选不注册的组件 最后包装要注册的组件
    protected AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) {
        if (!isEnabled(annotationMetadata)) {
            return EMPTY_ENTRY;
        }
        AnnotationAttributes attributes = getAttributes(annotationMetadata);
        List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);
        configurations = removeDuplicates(configurations);
        Set<String> exclusions = getExclusions(annotationMetadata, attributes);
        checkExcludedClasses(configurations, exclusions);
        configurations.removeAll(exclusions);
        configurations = getConfigurationClassFilter().filter(configurations);
        fireAutoConfigurationImportEvents(configurations, exclusions);
        return new AutoConfigurationEntry(configurations, exclusions);
    }

1、利用getAutoConfigurationEntry(annotationMetadata);给容器中批量导入一些组件
2、调用List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes)获取到所有需要导入到容器中的配置类
3、利用工厂加载 Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader)；得到所有的组件
4、从META-INF/spring.factories位置来加载一个文件。
    默认扫描我们当前系统里面所有META-INF/spring.factories位置的文件
例如
    spring-boot-autoconfigure-2.7.1.jar!/META-INF/spring.factories

给容器中导入的组件总量

按需开启自动配置项

虽然我们所有自动配置启动的时候默认全部加载。xxxxAutoConfiguration
按照条件装配规则（@Conditional），最终会按需配置。

 

标签：return,SpringBootApplication,metadata,annotationMetadata,组件,解析,class,configurati
来源： https://www.cnblogs.com/dabo-tian/p/16462558.html