Java中List根据对象的属性值进行数据库group by功能的操作

public class test {
    public static void main(String[] args) {

        List<Bill> list = new test().setObject();

        Set<String> set = new HashSet();

        for (Bill bills : list) {
            set.add(bills.getTradeTime().substring(0, 8));
        }

        List list1 = new ArrayList();
        int paySuccess = 0;
        int dfSuccess = 0;
        int fee = 0;
        int count = 0;
        //遍历set集合中的日期
        for (String a : set) {
            for (Bill bill : list) {
                if (a.equals(bill.getTradeTime().substring(0, 8))) {
                    paySuccess += bill.getMoney();
                    fee += bill.getFee();
                    count++;
                    if ("承兑或交易成功".equals(bill.getType()))
                        dfSuccess += bill.getMoney();
                }
            }
            Object[] objects = new Object[10];
            objects[0] = new BigDecimal(paySuccess);
            objects[1] = new BigDecimal(dfSuccess);
            objects[2] = new BigDecimal(fee);
            objects[3] = new BigDecimal(paySuccess-fee);
            objects[4] = a;
            list1.add(objects);
            System.out.println("支付成功金额：" + objects[0] + "\t" + "承兑或交易成功: " + objects[1] + "\t" + objects[4] + "\t" + "手续费：" + objects[2] + "\t" + "商户结算" +
                    "金额：" + objects[3] + "\t" + "交易笔数：" + count + "\t日期：" + a);
            paySuccess = 0;
            dfSuccess = 0;
            fee = 0;
            count = 0;
        }
        String date = null;
        System.out.println(date == null || date.isEmpty());
    }

    public List<Bill> setObject() {
        List<Bill> list = new ArrayList<Bill>();
        Bill bill = new Bill();
        bill.setTradeTime("201605050203");
        bill.setMoney(2);
        bill.setPayType("支付成功");
        bill.setType("承兑或交易成功");
        bill.setFee(1);
        list.add(bill);

        bill = new Bill();
        bill.setTradeTime("201605060203");
        bill.setMoney(3);
        bill.setType("");
        bill.setPayType("支付成功");
        bill.setFee(1);
        list.add(bill);

        bill = new Bill();
        bill.setMoney(4);
        bill.setTradeTime("201605050203");
        bill.setPayType("支付成功");
        bill.setType("承兑或交易成功");
        bill.setFee(1);
        list.add(bill);

        bill = new Bill();
        bill.setType("");
        bill.setPayType("支付成功");
        bill.setTradeTime("201605060203");
        bill.setMoney(4);
        bill.setFee(1);
        list.add(bill);
        return list;
    }
}

class Bill {
    int money;
    String type;
    String tradeTime;
    String payType;
    int fee;

    public String getPayType() {
        return payType;
    }

    public void setPayType(String payType) {
        this.payType = payType;
    }

    public int getMoney() {
        return money;
    }

    public void setMoney(int money) {
        this.money = money;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public String getTradeTime() {
        return tradeTime;
    }

    public void setTradeTime(String tradeTime) {
        this.tradeTime = tradeTime;
    }

    public int getFee() {
        return fee;
    }

    public void setFee(int fee) {
        this.fee = fee;
    }

    @Override
    public String toString() {
        return "Bill{" +
                "money=" + money +
                ", type='" + type + '\'' +
                ", tradeTime='" + tradeTime + '\'' +
                ", payType='" + payType + '\'' +
                '}';
    }
}

我的思路是先用set集合对对象的某个属性中不重复的值进行筛选，然后进行计算

 

如果有更好的方法请在下面留言！