Java8flatMap()合并多个list为一个list

// 例一
List<Integer> list = ImmutableList.of(1, 3, 5);
list = list.stream().flatMap(l -> {
    List<Integer> list1 = new ArrayList<>();
    list1.add(l + 1);
    list1.add(l + 2);
    return list1.stream();
}).collect(Collectors.toList());
System.out.println(list);// [2, 3, 4, 5, 6, 7]

// 例二
List<List<Map<String,Object>>> lists = ImmutableList.of(
                ImmutableList.of(
                        ImmutableMap.of("a", 1, "b", 2), ImmutableMap.of("a", 2, "b", 3)
                ),
                ImmutableList.of(
                        ImmutableMap.of("a", 3, "b", 4), ImmutableMap.of("a", 4, "b", 5)
                ),
                ImmutableList.of(
                        ImmutableMap.of("a", 5, "b", 6), ImmutableMap.of("a", 6, "b", 7)
                )
        );
// 将多个list合并为一个list
List<Map<String,Object>> list = lists.stream().flatMap(Collection::stream).collect(Collectors.toList());// [{a=1, b=2}, {a=2, b=3}, {a=3, b=4}, {a=4, b=5}, {a=5, b=6}, {a=6, b=7}]