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！