Java 代码优化：提升 getLevelSubtotal 方法性能

private ComputeResultExportDTO getLevelSubtotal(final String levelName, final String evaluationId, final StatisticsResultDTO levelOverallBigDecimal, final StatisticsResultDTO statisticsResultDTO, final Map<String, Map<String, List>> subtotalGroup, final Map<String, Map<String, BigDecimal>> democracyLevelSubtotalOverall) {

final ComputeResultExportDTO computeResultExportDTO =
    createComputeResultExportDTO(LEVEL_SUBTOTAL, evaluationId, statisticsResultDTO);
computeResultExportDTO.setTotalScore(levelOverallBigDecimal.getCalculationResultValue());
computeResultExportDTO.setSuggestedLevel(getSuggested(subtotalGroup.get(statisticsResultDTO.getEmpCode()).get(levelName)));
computeResultExportDTO.setDemocraticTotalScore(
    Optional.ofNullable(democracyLevelSubtotalOverall.get(statisticsResultDTO.getEmpName() + Constants.SPLIT_FLAG + statisticsResultDTO.getEmpCode()))
        .map(map -> map.get(levelName))
        .orElse(null));
computeResultExportDTO.setLevelGroup(levelName);
return computeResultExportDTO;

}