apollo-client/src/main/java/com/ctrip/framework/apollo/spring/spi/DefaultConfigPropertySourcesProcessorHelper.java/DefaultConfigPropertySourcesProcessorHelper/postProcessBeanDefinitionRegistry
class DefaultConfigPropertySourcesProcessorHelper:  @Override
  public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
    Map<String, Object> propertySourcesPlaceholderPropertyValues = new HashMap<>();
    // to make sure the default PropertySourcesPlaceholderConfigurer's priority is higher than PropertyPlaceholderConfigurer
    propertySourcesPlaceholderPropertyValues.put("order", 0);

    BeanRegistrationUtil.registerBeanDefinitionIfNotExists(registry, PropertySourcesPlaceholderConfigurer.class.getName(),
        PropertySourcesPlaceholderConfigurer.class, propertySourcesPlaceholderPropertyValues);
    BeanRegistrationUtil.registerBeanDefinitionIfNotExists(registry, ApolloAnnotationProcessor.class.getName(),
        ApolloAnnotationProcessor.class);
    BeanRegistrationUtil.registerBeanDefinitionIfNotExists(registry, SpringValueProcessor.class.getName(),
        SpringValueProcessor.class);

    processSpringValueDefinition(registry);
  }