computeIfAbsent将list转成多层map

Map<String, Map<String, EnergyDosageSummary>> list2map(List<EnergyDosageSummary> list) {
    list = list.stream().sorted(Comparator.comparing(EnergyDosageSummary::getCostCenter)).collect(Collectors.toList());
    //costCenter-feeType-bean
    Map<String, Map<String, EnergyDosageSummary>> resultMap = new HashMap<>(list.size());
    for (EnergyDosageSummary summary : list) {
        resultMap.computeIfAbsent(summary.getCostCenter(), key -> new HashMap<>()).put(summary.getFeeType(), summary);
    }
    return resultMap;
}