@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Configuration {
  String value() default "";
}

/**
 * Post-processes a BeanFactory in search of Configuration class BeanDefinitions;
 * any candidates are then enhanced by a {@link ConfigurationClassEnhancer}.
 * Candidate status is determined by BeanDefinition attribute metadata.
 * @see ConfigurationClassEnhancer
 */
public void enhanceConfigurationClasses(ConfigurableListableBeanFactory beanFactory) {
  Map<String, AbstractBeanDefinition> configBeanDefs = new LinkedHashMap<String, AbstractBeanDefinition>();
  for (String beanName : beanFactory.getBeanDefinitionNames()) {
    BeanDefinition beanDef = beanFactory.getBeanDefinition(beanName);
    if (ConfigurationClassUtils.isFullConfigurationClass(beanDef)) {
      //省略部分代碼
      configBeanDefs.put(beanName, (AbstractBeanDefinition) beanDef);
    }
  }
  if (configBeanDefs.isEmpty()) {
    // nothing to enhance -> return immediately
    return;
  }
  ConfigurationClassEnhancer enhancer = new ConfigurationClassEnhancer();
  for (Map.Entry<String, AbstractBeanDefinition> entry : configBeanDefs.entrySet()) {
    AbstractBeanDefinition beanDef = entry.getValue();
    // If a @Configuration class gets proxied, always proxy the target class
    beanDef.setAttribute(AutoProxyUtils.PRESERVE_TARGET_CLASS_ATTRIBUTE, Boolean.TRUE);
    try {
      // Set enhanced subclass of the user-specified bean class
      Class<?> configClass = beanDef.resolveBeanClass(this.beanClassLoader);
      Class<?> enhancedClass = enhancer.enhance(configClass, this.beanClassLoader);
      if (configClass != enhancedClass) {
        //省略部分代碼
        beanDef.setBeanClass(enhancedClass);
      }
    }
    catch (Throwable ex) {
      throw new IllegalStateException(
       "Cannot load configuration class: " + beanDef.getBeanClassName(), ex);
    }
  }
}

Class<?> enhancedClass = enhancer.enhance(configClass, this.beanClassLoader);

beanDef.setBeanClass(enhancedClass);

/**
 * Creates a new CGLIB {@link Enhancer} instance.
 */
private Enhancer newEnhancer(Class<?> superclass, ClassLoader classLoader) {
  Enhancer enhancer = new Enhancer();
  enhancer.setSuperclass(superclass);
  enhancer.setInterfaces(new Class<?>[] {EnhancedConfiguration.class});
  enhancer.setUseFactory(false);
  enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
  enhancer.setStrategy(new BeanFactoryAwareGeneratorStrategy(classLoader));
  enhancer.setCallbackFilter(CALLBACK_FILTER);
  enhancer.setCallbackTypes(CALLBACK_FILTER.getCallbackTypes());
  return enhancer;
}

// The callbacks to use. Note that these callbacks must be stateless.
private static final Callback[] CALLBACKS = new Callback[] {
    new BeanMethodInterceptor(),
    new BeanFactoryAwareMethodInterceptor(),
    NoOp.INSTANCE
};
private static final ConditionalCallbackFilter CALLBACK_FILTER = 
    new ConditionalCallbackFilter(CALLBACKS);

@Override
public boolean isMatch(Method candidateMethod) {
  return BeanAnnotationHelper.isBeanAnnotated(candidateMethod);
}
//BeanAnnotationHelper
public static boolean isBeanAnnotated(Method method) {
  return AnnotatedElementUtils.hasAnnotation(method, Bean.class);
}

@Override
public boolean isMatch(Method candidateMethod) {
  return (candidateMethod.getName().equals("setBeanFactory") &&
      candidateMethod.getParameterTypes().length == 1 &&
      BeanFactory.class == candidateMethod.getParameterTypes()[0] &&
      BeanFactoryAware.class.isAssignableFrom(candidateMethod.getDeclaringClass()));
}

@Configuration
public class MyBeanConfig {
  @Bean
  public Country country(){
    return new Country();
  }
  @Bean
  public UserInfo userInfo(){
    return new UserInfo(country());
  }
}

//首先通過反射從增強的 Configuration 注解類中獲取 beanFactory
ConfigurableBeanFactory beanFactory = getBeanFactory(enhancedConfigInstance);
//然后通過方法獲取 beanName，默認為方法名，可以通過 @Bean 注解指定
String beanName = BeanAnnotationHelper.determineBeanNameFor(beanMethod);
//確定這個 bean 是否指定了代理的范圍
//默認下面 if 條件 false 不會執(zhí)行
Scope scope = AnnotatedElementUtils.findMergedAnnotation(beanMethod, Scope.class);
if (scope != null && scope.proxyMode() != ScopedProxyMode.NO) {
  String scopedBeanName = ScopedProxyCreator.getTargetBeanName(beanName);
  if (beanFactory.isCurrentlyInCreation(scopedBeanName)) {
    beanName = scopedBeanName;
  }
}
//中間跳過一段 Factorybean 相關代碼
//判斷當前執(zhí)行的方法是否為正在執(zhí)行的 @Bean 方法
//因為存在在 userInfo() 方法中調用 country() 方法
//如果 country() 也有 @Bean 注解，那么這個返回值就是 false.
if (isCurrentlyInvokedFactoryMethod(beanMethod)) {
  // 判斷返回值類型，如果是 BeanFactoryPostProcessor 就寫警告日志
  if (logger.isWarnEnabled() &&
      BeanFactoryPostProcessor.class.isAssignableFrom(beanMethod.getReturnType())) {
    logger.warn(String.format(
      "@Bean method %s.%s is non-static and returns an object " +
      "assignable to Spring's BeanFactoryPostProcessor interface. This will " +
      "result in a failure to process annotations such as @Autowired, " +
      "@Resource and @PostConstruct within the method's declaring " +
      "@Configuration class. Add the 'static' modifier to this method to avoid " +
      "these container lifecycle issues; see @Bean javadoc for complete details.",
      beanMethod.getDeclaringClass().getSimpleName(), beanMethod.getName()));
  }
  //直接調用原方法創(chuàng)建 bean
  return cglibMethodProxy.invokeSuper(enhancedConfigInstance, beanMethodArgs);
}
//如果不滿足上面 if，也就是在 userInfo() 中調用的 country() 方法
return obtainBeanInstanceFromFactory(beanMethod, beanMethodArgs, beanFactory, beanName);

currentlyInvokedFactoryMethod.set(factoryMethod);
return factoryMethod.invoke(factoryBean, args);

@Component
public class MyBeanConfig {
  @Bean
  public Country country(){
    return new Country();
  }
  @Bean
  public UserInfo userInfo(){
    return new UserInfo(country());
  }
}

@Component
public class MyBeanConfig {
  @Autowired
  private Country country;
  @Bean
  public Country country(){
    return new Country();
  }
  @Bean
  public UserInfo userInfo(){
    return new UserInfo(country);
  }
}