apollo-client/src/main/java/com/ctrip/framework/apollo/spring/boot/ApolloApplicationContextInitializer.java/ApolloApplicationContextInitializer/fillSystemPropertyFromEnvironment
class ApolloApplicationContextInitializer:  private void fillSystemPropertyFromEnvironment(ConfigurableEnvironment environment, String propertyName) {
    if (System.getProperty(propertyName) != null) {
      return;
    }

    String propertyValue = environment.getProperty(propertyName);

    if (Strings.isNullOrEmpty(propertyValue)) {
      return;
    }

    System.setProperty(propertyName, propertyValue);
  }