java用根据月份、类型汇总求和并修改

public int sumByList(){
    List<EnergyNaturalGas> list = energyNaturalGasMapper.selectEnergyNaturalGasList2();
     Map<String, Map<String, BigDecimal>> groupByResult = list.stream()
            .collect(
                    Collectors.groupingBy(
                            EnergyNaturalGas::getTime,
                            Collectors.groupingBy(
                                    EnergyNaturalGas::getProvideType,
                                    Collectors.reducing(
                                            BigDecimal.ZERO,
                                            EnergyNaturalGas::getEnergyNumber,
                                            BigDecimal::add
                                    )
                            )
                    )
            );

    groupByResult.forEach((time, provideTypeMap) -> {
            provideTypeMap.forEach((provideType, sumTotal) -> {
                EnergyNaturalGas provider = new EnergyNaturalGas();
                provider.setTime(time);
                provider.setProvideType(provideType);
                provider.setMonthlySummary(sumTotal);
                energyNaturalGasMapper.updateEnergyNaturalGasByParm(provider);
            });
        });
    return 1;
}