Stream流分组,统计,求和
public class Test { public static void main(String[] args) { List<OrdersDO> list = new ArrayList<>();//查询昨天一天的所有交易 OrdersDO o1 = new OrdersDO(); o1.setAppId(1L); o1.setTradeAmount(100L); o1.setStatus(1); list.add(o1); OrdersDO o2 = new OrdersDO(); o2.setAppId(5L); o2.setTradeAmount(300L); o2.setStatus(2); list.add(o2); OrdersDO o3 = new OrdersDO(); o3.setAppId(1L); o3.setTradeAmount(100L); o3.setStatus(3); list.add(o3); OrdersDO o4 = new OrdersDO(); o4.setAppId(5L); o4.setTradeAmount(300L); o4.setStatus(4); list.add(o4); OrdersDO o5 = new OrdersDO(); o5.setAppId(5L); o5.setTradeAmount(300L); o5.setStatus(4); list.add(o5); //统计每个应用实际支付总额 Map<Long, Long> tradeAmountMap = list.stream().filter(o->o.getStatus()==2) .collect(Collectors.groupingBy(OrdersDO::getAppId, Collectors.summingLong(OrdersDO::getTradeAmount))); System.out.println(tradeAmountMap); //统计每个应用取消总额 Map<Long, Long> cancelAmountMap = list.stream() .collect(Collectors.groupingBy(OrdersDO::getAppId, Collectors.summingLong(OrdersDO::getTradeAmount))); System.out.println(cancelAmountMap); //统计每个应用下交易笔数 Map<Long, Long> appTradeNum = list.stream().collect(Collectors.groupingBy(OrdersDO::getAppId, Collectors.counting())); System.out.println(appTradeNum); //统计每个应用每种状态下交易笔数 Map<Long, Map<Integer, Long>> tradeNumMap = list.stream(). collect(Collectors.groupingBy(OrdersDO::getAppId, Collectors.groupingBy(OrdersDO::getStatus, Collectors.counting()))); System.out.println(tradeNumMap); //每个应用下交易笔数按数量排序 Map<Long,Long> finalMap = new LinkedHashMap<>(); appTradeNum.entrySet().stream().sorted(Map.Entry.<Long, Long>comparingByValue().reversed()).forEachOrdered(e->finalMap.put(e.getKey(),e.getValue())); System.out.println(finalMap); } }