我认为您是在Collectors.mapping之后，可以将其作为第二个参数传递给groupingBy
完整的例子
import java.util.AbstractMap;import java.util.List;import java.util.Map;import static java.util.Arrays.asList;import static java.util.Map.Entry;import static java.util.stream.Collectors.*;public class SO { public static void main(String... args) { List<Album> albums = asList( new Album( asList( new Artist("bob"), new Artist("tom") ) ), new Album(asList(new Artist("bill"))) ); Map<Artist, List<Album>> x = albums.stream() .flatMap(album -> album.getArtist().stream().map(artist -> pair(artist, album))) .collect(groupingBy(Entry::getKey, mapping(Entry::getValue, toList()))); x.entrySet().stream().forEach(System.out::println); } static class Artist { private final String name; Artist(String name) { this.name = name; } public String toString() {return name;} } static class Album { private List<Artist> artist; Album(List<Artist> artist) { this.artist = artist; } List<Artist> getArtist() { return artist; } } private static <T,U> AbstractMap.SimpleEntry<T,U> pair(T t, U u) { return new AbstractMap.SimpleEntry<T,U>(t,u); }}
