java stream 合并多个 List 列表

import java.util.Arrays;
import java.util.Collection;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Code {

    public static void main(String[] args) {
        List<Integer> list1 = Arrays.asList(1, 2, 3);
        List<Integer> list2 = Arrays.asList(4, 5, 6);
        List<Integer> list3 = Arrays.asList(7, 8, 9);

        List<Integer> mergedList = Stream.of(list1, list2, list3).flatMap(Collection::stream).collect(Collectors.toList());

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

    }
}