Java 8 Streams - How to get top 3 sums from list of list of integer

I have a list of list of integers as below:

 List<List<Integer>> integers = Arrays.asList(
                Arrays.asList(8, 9, 4, 5, 6), // sum is 32
                Arrays.asList(10, 0, 6, 3, 7), //sum is 26
                Arrays.asList(1, 9, 2, 16, 3), //sum is 31
                Arrays.asList(2, 22, 4, 5), //sum is 33
                Arrays.asList(15, 6)); //sum is 21

I need to return max 3 sums calculated from each nested list using stream API. As given above I need to return list containing 33,32,31.

I tried with few stream methods but always gets syntax error. Please help on how to achieve desire result.

Solution

import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

public class TopThree {

    public static void main(String args[]) {
        List<List<Integer>> integers = List.of(List.of( 8,  9, 4,  5, 6),
                                               List.of(10,  0, 6,  3, 7),
                                               List.of( 1,  9, 2, 16, 3),
                                               List.of( 2, 22, 4,  5),
                                               List.of(15,  6));
        List<Integer> top3 = integers.stream()
                                     .map(l -> l.stream().reduce(0, Integer::sum))
                                     .collect(Collectors.toList())
                                     .stream()
                                     .sorted(Comparator.reverseOrder())
                                     .limit(3L)
                                     .collect(Collectors.toList());
        System.out.println(top3);
    }
}

The first stream method returns a stream where every element has type List<Integer>.
The map method gets the sum of the elements in each [inner] list.
The first collect creates a single List<Integer> where every element is the sum of one of the [inner] Lists of integers.
This list [of sums] is sorted in descending order.
Method limit takes only the first three elements of the list [of sums].
The last collect creates a List<Integer> containing the top three sums (as requested).