apollo-client/src/main/java/com/ctrip/framework/apollo/spring/property/PlaceholderHelper.java/PlaceholderHelper/isNormalizedPlaceholder
class PlaceholderHelper:  private boolean isNormalizedPlaceholder(String propertyString) {
    return propertyString.startsWith(PLACEHOLDER_PREFIX) && propertyString.contains(PLACEHOLDER_SUFFIX);
  }