Int array get duplicate data

package com.javaming.study.easyexcel.controller;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;

import static java.util.Arrays.sort;

public class OfferTest {
    public static void main(String[] args) {
        int[] a = {1, 2, 3, 4, 2, 3,1,12,1};

        int[] repeatNumbe2 = findRepeatNumbe2(a);
        System.out.println(Arrays.toString(repeatNumbe2));


    }

    
    // Method 2
    public static int[] findRepeatNumbe2(int[] nums) {
        List<Integer> numList = new ArrayList<>();
        for (int num : nums) {
            numList.add(num);
        }
        Map<Integer, Long> collect = numList.stream()
                .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));// grouping list  Display total 

        List<Integer> result = collect.entrySet().stream()
                .filter(e -> e.getValue() > 1) // The total is greater than 1 Filter 
                .map(Map.Entry::getKey) // Get value transfer list
                .collect(Collectors.toList());

        int[] a = new int[result.size()];
        // Set array 
        for (int i = 0; i < a.length; i++) {
            a[i] = result.get(i);
        }

        return a;


    }
}