我对这段代码有一些问题。
我正在使用人口统计学列表创建地图,但有时我有重复的列表元素。可以看到我在哪里做错了吗?
问候。
public Map<DemoType, List<Demography>> demoTypeToDemosList(final Long campaignId, final MediaType mediaType) {
List<MappedDemoDTO> mappedDemosList = demoTypeCampaignService.getMappedDemosByMediaTypeAndCampaignIdOrderByOrdinalRankAsc(mediaType, campaignId);
final Set<Long> demoIds = mappedDemosList.stream().map(MappedDemoDTO::getMappedId).collect(Collectors.toSet());
DemographyProviderService serviceByProviderAndMediaType = demographyFactory.getServiceByProviderAndMediaType(Provider.PROVIDER, mediaType);
final List<Demo> demos = serviceByProviderAndMediaType.getDemoByExternalIds(demoIds);
Map<DemoType, List<Demography>> demoTypeToDemosMap = new EnumMap<>(DemoType.class);
mappedDemosList.forEach(mappedDemo -> demos.stream()
.filter(demo -> mappedDemo.getMappedId().equals(demo.getId()))
.findFirst()
.ifPresent(demo -> {
List<Demography> demosList = demoTypeToDemosMap.computeIfAbsent(mappedDemo.getDemoType(), f -> new ArrayList<>());
demo.setId(mappedDemo.getDemoId());
demosList.add(demo);
}));
return demoTypeToDemosMap;
}
最佳答案
阅读computeIfAbsent
的文档:
返回与指定键关联的当前(现有的或计算的)值;如果计算的值为null,则返回null
这个:
List<Demography> demosList = demoTypeToDemosMap.computeIfAbsent(mappedDemo.getDemoType(), f -> new ArrayList<>());
如果密钥不在
ArrayList
或现有密钥中,则将返回一个新的Map
,您稍后将其添加到该密钥中:demosList.add(demo);
关于java - 将值复制到Map <DemoType,List <Demography >>,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/52016944/