code: @Override
      public SequenceRange get(String schemaName, String tableName, int step) throws Exception {
          Map<String, String> param = new HashMap<>();
          param.put("clientId", clientId);
          param.put("accessToken", accessToken);
          param.put("schemaName", schemaName);
          param.put("tableName", tableName);
          param.put("step", String.valueOf(step));
          String result = HttpUtils.sendPost(accessUrl, param);
          Map<String, String> resultMap = parseHttpKvString(result);
          if (resultMap.isEmpty()) {
              return null;
          } else {
              if (resultMap.get("errorCode") != null) {
                  authorize();
                  result = HttpUtils.sendPost(accessUrl, param);
                  resultMap = parseHttpKvString(result);
                  if (resultMap.get("errorCode") != null) {
                      throw new GetSequenceFailedException("clientId:" + clientId
                                                           + " access data failed, return message is:" + result);
                  }
              }
              SequenceRange sequenceRange = new SequenceRange();
              sequenceRange.setBeginValue(parseLong(resultMap.get("beginValue")));
              sequenceRange.setEndValue(parseLong(resultMap.get("endValue")));
              return sequenceRange;
          }
      }
docs: param: clientId= &accessToken= &schemaName= &tableName= &step=
  return: beginValue= &endValue= &errorCode= &errorMessage=