JAVA使用随机数进行概率抽奖

网站现有一抽奖功能，已经定义好奖品，每个奖品都有对应的中奖概率。通过奖品概率随机进行抽奖

1. 每个奖品都有对应的中奖概率，先对所有奖品中奖概率求和
2. 计算出每个奖品在0-1之间所占的区间块
3. 随机产生0-1之间的随机数，随机数落在哪个区间，就是中奖哪个
   例如现有以下奖品：
   奖品A 中奖概率为 0.1
   奖品B 中奖概率为 0.01
   奖品C 中奖概率为 0.001
   奖品D 中奖概率为 0.8

第一步：求出概率总和 0.1+0.01+0.001+0.8 = 0.911
第二步：计算每个奖品的所占区间块
奖品A： 0.1 / 0.911 = 0.1098
奖品B： （0.1+0.01）/ 0.911 = 0.1207
奖品C：（0.1+0.11+0.001）/ 0.911 = 0.1218
奖品D：（0.1+0.11+0.001+0.8）/ 0.911 = 1
则：
奖品A的所占区间为：0~0.1098
奖品B的所占区间为：0.1098~0.1207
奖品C的所占区间为：0.1207~0.1218
奖品D的所占区间为：0.1218~1

代码如下

/**
 * 奖品实体类
 */
public class Award{
    public Award(){}
    public Award(String awardTitle,double probability){
        this.awardTitle = awardTitle;
        this.probability = probability;
    }
    /**奖品ID**/
    private String awardId;
    /**奖品名**/
    private String awardTitle;
    /**中奖概率**/
    private double probability;
    public String getAwardId() {
        return awardId;
    }
    public void setAwardId(String awardId) {
        this.awardId = awardId;
    }
    public String getAwardTitle() {
        return awardTitle;
    }
    public void setAwardTitle(String awardTitle) {
        this.awardTitle = awardTitle;
    }
    public double getProbability() {
        return probability;
    }
    public void setProbability(double probability) {
        this.probability = probability;
    }
}

public class LotteryUtil {

    /**
     * 抽奖，获取中奖奖品
     * @param awardList 奖品及中奖概率列表
     * @return 中奖商品
     */
    public static Award lottery(List<Award> awardList) {
        if(awardList.isEmpty()){
            throw new AwardListIsEmptyException();
        }
        //奖品总数
        int size = awardList.size();

        //计算总概率
        double sumProbability = 0d;
        for (Award award : awardList) {
            sumProbability += award.getProbability();
        }

        //计算每个奖品的概率区间
        //例如奖品A概率区间0-0.1  奖品B概率区间 0.1-0.5 奖品C概率区间0.5-1
        //每个奖品的中奖率越大，所占的概率区间就越大
        List<Double> sortAwardProbabilityList = new ArrayList<Double>(size);
        Double tempSumProbability = 0d;
        for (Award award : awardList) {
            tempSumProbability += award.getProbability();
            sortAwardProbabilityList.add(tempSumProbability / sumProbability);
        }

        //产生0-1之间的随机数
        //随机数在哪个概率区间内，则是哪个奖品
        double randomDouble = Math.random();
        //加入到概率区间中，排序后，返回的下标则是awardList中中奖的下标
        sortAwardProbabilityList.add(randomDouble);
        Collections.sort(sortAwardProbabilityList);
        int lotteryIndex = sortAwardProbabilityList.indexOf(randomDouble);
        return awardList.get(lotteryIndex);
    }

    public static void main(String[] args) {
        List<Award> awardList = new ArrayList<Award>();
        awardList.add(new Award("10个积分",0.35d));
        awardList.add(new Award("33个积分",0.25d));
        awardList.add(new Award("5元红包",0.002d));
        awardList.add(new Award("20元话费",0.003d));
        awardList.add(new Award("京东100元购物卡",0.0005d));
        awardList.add(new Award("未中奖",0.1d));

        Map<String,Integer> result = new HashMap<String,Integer>();
        for(int i=0;i<10000;i++){
            Award award = lottery(awardList);
            String title = award.getAwardTitle();
            Integer count = result.get(title);
            result.put(title, count == null ? 1 : count + 1);
        }

        for (Entry<String, Integer> entry : result.entrySet()) {
            System.out.println(entry.getKey() + ", count=" + entry.getValue() +", reate="+ entry.getValue()/10000d);
        }
    }
}

测试结果