@Override
  public Map<String, TemporalInfo> getFields() {
    Map<String, TemporalInfo> mapProperties;
    String partialResponseFields = m_uriInfo.getQueryParameters().getFirst(QueryLexer.QUERY_FIELDS);
    if (partialResponseFields == null) {
      mapProperties = Collections.emptyMap();
    } else {
      Set<String> setMatches = new HashSet<>();
      // Pattern basically splits a string using ',' as the deliminator unless ',' is between '[' and ']'.
      // Actually, captures char sequences between ',' and all chars between '[' and ']' including ','.
      Pattern re = Pattern.compile("[^,\\[]*?\\[[^\\]]*?\\]|[^,]+");
      Matcher m = re.matcher(partialResponseFields);
      while (m.find()){
        for (int groupIdx = 0; groupIdx < m.groupCount() + 1; groupIdx++) {
          setMatches.add(m.group(groupIdx));
        }
      }

      mapProperties = new HashMap<>(setMatches.size());
      for (String field : setMatches) {
        TemporalInfo temporalInfo = null;
        if (field.contains("[")) {
          String[] temporalData = field.substring(field.indexOf('[') + 1,
              field.indexOf(']')).split(",");
          field = field.substring(0, field.indexOf('['));
          long start = Long.parseLong(temporalData[0].trim());
          long end   = -1;
          long step  = -1;
          if (temporalData.length >= 2) {
            end = Long.parseLong(temporalData[1].trim());
            if (temporalData.length == 3) {
              step = Long.parseLong(temporalData[2].trim());
            }
          }
          temporalInfo = new TemporalInfoImpl(start, end, step);
        }
        mapProperties.put(field, temporalInfo);
      }
    }

    return mapProperties;
  }
Constructor.

@param headers           http headers
@param body              http body
@param uriInfo           uri information
@param resource          associated resource definition
ambari-server/src/main/java/org/apache/ambari/server/api/services/BaseRequest.java