带有内部列表的列表以映射Java Stream Api

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        List<List<Integer>> nestedList = new ArrayList<>();
        nestedList.add(Arrays.asList(1, 2, 3));
        nestedList.add(Arrays.asList(4, 5, 6));
        nestedList.add(Arrays.asList(7, 8, 9));

        List<Integer> flattenedList = nestedList.stream()
                .flatMap(List::stream)
                .collect(Collectors.toList());

        System.out.println(flattenedList);
        // 输出: [1, 2, 3, 4, 5, 6, 7, 8, 9]
    }
}