Java权重随机算法，根据权重随机获取一个业务对象

//AdvertPushDTO为业务对象，getWeight()获取权重值
private AdvertPushDTO weightRamdom(List<AdvertPushDTO> list){
    int weightSum = 0;
    for (AdvertPushDTO dto : list) {
        weightSum += dto.getWeight();
    }
    if (weightSum <= 0) {
        System.err.println("错误: weightSum=" + weightSum);
        return null;
    }
    Integer n = new Random().nextInt(weightSum); // n的值为 [0, weightSum)
    Integer m = 0;
    for (AdvertPushDTO dto : list) {
        if (m <= n && n < m + dto.getWeight()) {
                return dto; //返回结果
        }
        m += dto.getWeight();
    }
    return null;
}