spring boot@EnableXXXX注解编程模型讲解

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(XXXX.class)
public @interface EnableDiscoveryClient {
   /**
    * If true, the ServiceRegistry will automatically register the local server.
    */
   boolean autoRegister() default true;
}

org.springframework.context.support.AbstractApplicationContext#refresh
org.springframework.context.support.AbstractApplicationContext#invokeBeanFactoryPostProcessors
org.springframework.context.annotation.ConfigurationClassPostProcessor#postProcessBeanDefinitionRegistry
org.springframework.context.annotation.ConfigurationClassPostProcessor#processConfigBeanDefinitions（主线代码，必看）

public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
  //定义@Conguration注解修饰的类注册信息列表
 List<BeanDefinitionHolder> configCandidates = new ArrayList<>();
 String[] candidateNames = registry.getBeanDefinitionNames();
//检查当前context中所有的bean注册信息
 for (String beanName : candidateNames) {
    BeanDefinition beanDef = registry.getBeanDefinition(beanName);
    if (ConfigurationClassUtils.isFullConfigurationClass(beanDef) ||
          ConfigurationClassUtils.isLiteConfigurationClass(beanDef)) {
       if (logger.isDebugEnabled()) {
          logger.debug("Bean definition has already been processed as a configuration class: " + beanDef);
       }
    }
     //检查class是否是@Conguration注解修饰的类，包括被“继承”@Conguration注解的注解，例如@SpringBootConguration，具体可以跟踪ConfigurationClassUtils.checkConfigurationClassCandidate实现
    else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) {
       configCandidates.add(new BeanDefinitionHolder(beanDef, beanName));
    }
 }
 // Return immediately if no @Configuration classes were found
 if (configCandidates.isEmpty()) {
    return;
 }
 // Sort by previously determined @Order value, if applicable
  //对配置类排序，顺序由Ordered接口决定
 configCandidates.sort((bd1, bd2) -> {
    int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition());
    int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition());
    return Integer.compare(i1, i2);
 });
//......略略略
 // Parse each @Configuration class
  //处理每一个配置类
 ConfigurationClassParser parser = new ConfigurationClassParser(
       this.metadataReaderFactory, this.problemReporter, this.environment,
       this.resourceLoader, this.componentScanBeanNameGenerator, registry);
 Set<BeanDefinitionHolder> candidates = new LinkedHashSet<>(configCandidates);
 Set<ConfigurationClass> alreadyParsed = new HashSet<>(configCandidates.size());
 do {
     //解析处理配置类逻辑
    parser.parse(candidates);
     //......略略略
 }
 while (!candidates.isEmpty());
//......略略略
}

org.springframework.context.annotation.ConfigurationClassParser#parse(java.util.Set

String[] importClassNames = selector.selectImports(currentSourceClass.getMetadata());

else if (candidate.isAssignable(ImportBeanDefinitionRegistrar.class)) {
   // Candidate class is an ImportBeanDefinitionRegistrar ->
   // delegate to it to register additional bean definitions
   Class<?> candidateClass = candidate.loadClass();
   ImportBeanDefinitionRegistrar registrar =
         BeanUtils.instantiateClass(candidateClass, ImportBeanDefinitionRegistrar.class);
   ParserStrategyUtils.invokeAwareMethods(
         registrar, this.environment, this.resourceLoader, this.registry);
         //将ImportBeanDefinitionRegistrar放入map缓存起来
   configClass.addImportBeanDefinitionRegistrar(registrar, currentSourceClass.getMetadata());
}

public void addImportBeanDefinitionRegistrar(ImportBeanDefinitionRegistrar registrar, AnnotationMetadata importingClassMetadata) {
   this.importBeanDefinitionRegistrars.put(registrar, importingClassMetadata);
}

// Process individual @Bean methods
//对配置类的@Bean方法处理逻辑
//获取所有@Bean标注的方法元信息，后续处理
Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
for (MethodMetadata methodMetadata : beanMethods) {
   configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
}

//处理@Configuration,递归寻找@Configuration，以及解析@Configuration里面的@Import、@Bean、@Component、@ImportResource等。
parser.parse(candidates);
parser.validate();
//获取parser中解析得到的所有配置类
Set<ConfigurationClass> configClasses = new LinkedHashSet<>(parser.getConfigurationClasses());
configClasses.removeAll(alreadyParsed);
// Read the model and create bean definitions based on its content
if (this.reader == null) {
   this.reader = new ConfigurationClassBeanDefinitionReader(
         registry, this.sourceExtractor, this.resourceLoader, this.environment,
         this.importBeanNameGenerator, parser.getImportRegistry());
}
//根据递归找出的配置类和解析配置类得到的信息，加载BeanDefinition
this.reader.loadBeanDefinitions(configClasses);

org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader#loadBeanDefinitions
org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader#loadBeanDefinitionsForConfigurationClass

private void loadBeanDefinitionsForConfigurationClass(
      ConfigurationClass configClass, TrackedConditionEvaluator trackedConditionEvaluator) {
   if (trackedConditionEvaluator.shouldSkip(configClass)) {
      String beanName = configClass.getBeanName();
      if (StringUtils.hasLength(beanName) && this.registry.containsBeanDefinition(beanName)) {
         this.registry.removeBeanDefinition(beanName);
      }
      this.importRegistry.removeImportingClass(configClass.getMetadata().getClassName());
      return;
   }
   if (configClass.isImported()) {
      registerBeanDefinitionForImportedConfigurationClass(configClass);
   }
   for (BeanMethod beanMethod : configClass.getBeanMethods()) {
       //利用@Bean的Method加载BeanDefinition
      loadBeanDefinitionsForBeanMethod(beanMethod);
   }
   loadBeanDefinitionsFromImportedResources(configClass.getImportedResources());
    //利用缓存的ImportBeanDefinitionRegistrar加载注册beandefintion
   loadBeanDefinitionsFromRegistrars(configClass.getImportBeanDefinitionRegistrars());
}

org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader#loadBeanDefinitionsFromRegistrars（以ImportBeanDefinitionRegistrar为例跟踪）
org.springframework.context.annotation.ImportBeanDefinitionRegistrar#registerBeanDefinitions（注册BeanDefinition信息到BeanFactory）