将两个ArrayLists并行合并为一个ArrayList？

import java.util.ArrayList;
import java.util.List;

public class ArrayListMerger {
    public static void main(String[] args) {
        List<Integer> list1 = new ArrayList<>();
        list1.add(1);
        list1.add(2);
        list1.add(3);

        List<Integer> list2 = new ArrayList<>();
        list2.add(4);
        list2.add(5);
        list2.add(6);

        List<Integer> mergedList = mergeArrayLists(list1, list2);
        System.out.println(mergedList);
    }

    public static List<Integer> mergeArrayLists(List<Integer> list1, List<Integer> list2) {
        return list1.parallelStream()
                .collect(ArrayList::new, ArrayList::add, ArrayList::addAll)
                .parallelStream()
                .collect(ArrayList::new, ArrayList::add, ArrayList::addAll)
                .parallelStream()
                .collect(ArrayList::new, ArrayList::add, ArrayList::addAll);
    }
}