Multimaps.java 文件源码

public static <K,V> ImmutableList<ImmutableMap<K, V>> flatten(ImmutableMultimap<K, V> src) {
    ImmutableList.Builder<ImmutableMap<K, V>> listBuilder=ImmutableList.builder();

    if (!src.isEmpty()) {
        ImmutableMap<K, Collection<V>> map = src.asMap();
        int entries=map.values().stream().reduce(1, (s,l) -> s*l.size(), (a,b) -> a*b);

        ImmutableList<Line<K,V>> lines = map.entrySet().stream()
                .map(e -> new Line<>(e.getKey(), e.getValue()))
                .collect(ImmutableList.toImmutableList());

        for (int i=0;i<entries;i++) {
            ImmutableMap.Builder<K, V> mapBuilder = ImmutableMap.builder();

            int fact=1;
            for (Line<K,V> line: lines) {
                mapBuilder.put(line.key, line.get((i/fact) % line.values.length));
                fact=fact*line.values.length;
            }

            listBuilder.add(mapBuilder.build());
        }
    }
    return listBuilder.build();
}