code: protected static List<String> getOriginalKeys(String sqlFragment) {
          List<String> keys = new ArrayList<String>();
          if (sqlFragment.contains("{")) {
              String key = sqlFragment.substring(sqlFragment.indexOf('{') + 1, sqlFragment.indexOf('}')).trim();
              keys.add(key);
              keys.addAll(getOriginalKeys(sqlFragment.substring(sqlFragment.indexOf('}') + 1)));
          }
          return keys;
      }
docs: 得到sql模式串中的原模原样的key