【框架源码】SpringBoot核心源码解读之自动配置源码分析

@Target({ElementType.TYPE})  //注解的作用范围，用在类，接口，注解等上面
@Retention(RetentionPolicy.RUNTIME) //注解生命周期，runtime，保留在运行时期
@Documented //可以被文档化
@Inherited //可以被子类继承
@SpringBootConfiguration  //里面是@Configuration属于配置类
@EnableAutoConfiguration  //启动自动配置功能
//配置扫描包
@ComponentScan(
    excludeFilters = {@Filter(
    type = FilterType.CUSTOM,
    classes = {TypeExcludeFilter.class}
), @Filter(
    type = FilterType.CUSTOM,
    classes = {AutoConfigurationExcludeFilter.class}
)}
)
public @interface SpringBootApplication

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage //自动配置包
@Import(AutoConfigurationImportSelector.class) //通过import导入满足条件的bean,并加载到spring的ioc容器里面
public @interface EnableAutoConfiguration 

@Import(AutoConfigurationPackages.Registrar.class) //把Registrar导入到spring容器里面

    //获取主程序所在的目录为位置，metadata是元注解信息
    @Override
    public void registerBeanDefinitions(AnnotationMetadata metadata,
        BeanDefinitionRegistry registry) {
      register(registry, new PackageImport(metadata).getPackageName());
    }

  //用于实现动态注册Bean的功能，【批量】导入对象到容器里，根据条件动态地选择需要注册的Bean，并加入Spring容器
  //实现ImportSelector接口，这个接口的selectImports方法会返回一个String数组，数组中的值就是要添加的组件的全类名
  public String[] selectImports(AnnotationMetadata annotationMetadata) {
    if (!isEnabled(annotationMetadata)) {
      return NO_IMPORTS;
    }
    //加载元数据信息
    AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
        .loadMetadata(this.beanClassLoader);
    //获取需要自动装载的类的信息
    AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(
        autoConfigurationMetadata, annotationMetadata);
    return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
  }

protected AutoConfigurationEntry getAutoConfigurationEntry(
      AutoConfigurationMetadata autoConfigurationMetadata,
      AnnotationMetadata annotationMetadata) {
    //判断是否启用了自动配置
    if (!isEnabled(annotationMetadata)) {
      return EMPTY_ENTRY;
    }
    AnnotationAttributes attributes = getAttributes(annotationMetadata);
    //获取候选自动配置类列表
    List<String> configurations = getCandidateConfigurations(annotationMetadata,
        attributes);
    //去除重复的自动配置类
    configurations = removeDuplicates(configurations);
    //获取需要排除的自动配置类列表
    Set<String> exclusions = getExclusions(annotationMetadata, attributes);
    //检查是否存在需要排除的自动配置类
    checkExcludedClasses(configurations, exclusions);
    //将需要排除的类从自动配置类列表中移除
    configurations.removeAll(exclusions);
    //获取配置类过滤器，对候选自动配置类列表进行过滤
    configurations = filter(configurations, autoConfigurationMetadata);
    //触发自动配置导入事件，并返回一个新的自动配置条目
    fireAutoConfigurationImportEvents(configurations, exclusions);
    return new AutoConfigurationEntry(configurations, exclusions);
  }

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

  public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";