apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/config/BizConfig.java/BizConfig/itemKeyLengthLimit
class BizConfig:  public int itemKeyLengthLimit() {
    int limit = getIntProperty("item.key.length.limit", DEFAULT_ITEM_KEY_LENGTH);
    return checkInt(limit, 5, Integer.MAX_VALUE, DEFAULT_ITEM_KEY_LENGTH);
  }