Java 8 将 List 转换为 Lookup Map

2022-01-22 00:00:00 lookup java-8 java java-stream collectors

我有一个电台列表，每个电台都有一个收音机列表.我需要创建一个电台到电台的查找地图.我知道如何使用 Java 8 流 forEach 来做到这一点:

I have a list of Station, in each Station there is a list of radios. I need to create a lookup Map of radio to Station. I know how to use Java 8 stream forEach to do it:

stationList.stream().forEach(station -> {
    Iterator<Long> it = station.getRadioList().iterator();
    while (it.hasNext()) {
        radioToStationMap.put(it.next(), station);
    }
});

但我相信应该有更简洁的方式，比如使用 Collectors.mapping().

But I believe there should be more concise way like using Collectors.mapping().

有人可以帮忙吗?

推荐答案

这应该可以工作，你不需要第三方.

This should work and you don't need third parties.

stationList.stream()
    .map(s -> s.getRadioList().stream().collect(Collectors.toMap(b -> b, b -> s)))
    .flatMap(map -> map.entrySet().stream())
    .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));

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