java8-collect操作實例

• 集合分組（根基對象某屬性）

  Map<Integer, List<OrderDetail>> collect = list.stream().collect(
  		Collectors.groupingBy(OrderDetail::getProGoodsId));
  

  • 計算分組中某字段之和

    Map<String,Integer> goodsSum=list().stream().collect(Collectors.groupingBy(OrderDetail::getGoodsSku,Collectors.summingInt(SalesOrderDetail::getGoodsSum)));
    

  • 獲取分組後組的數量

    int prdocutSize = list.stream().collect(Collectors.groupingBy(OrderDetail::getGoodsSku)).size();
    

  • 計算分組後每組對象的數量

    Map<String, Long> mobileMap = list.stream().collect(Collectors.groupingBy(Customer::getMobile, Collectors.counting()));
    

• 計算集合中某屬性的和

  list.stream().collect(Collectors.summingInt(OrderDetail::getGoodsSum)).intValue();
  

• List轉Map(key重複時取第一個對象)
  • 方式一

    Map<String, SysUser> userMap=list.stream().collect(Collectors.toMap(SysUser::getLoginName,sysUser->sysUser,(key1,key2)->key1));
    

  • 方式二

    Map<Integer,OrderDataVo> orderDataMap = orderDatas.stream().collect(Collectors.groupingBy(OrderDataVo::getSkuId,Collectors.collectingAndThen(Collectors.toList(), value->value.get(0))));
    

• 將對象的某兩個屬性作爲KEY:VALUE
  • 方式一

    Map<String,Integer> map1 = goodsVo.stream().collect(Collectors.toMap(pushGoodsInveroyVo ->pushGoodsInveroyVo.getSquareItemId(),PushGoodsInveroyVo::getNum));
    

  • 方式二

    Map<String,Integer> map2 = goodsVo.stream().collect(Collectors.toMap(PushGoodsInveroyVo::getSquareItemId, PushGoodsInveroyVo::getNum));
    

  • 方式三

    Map<String,Integer> map3 = goodsVo.stream().collect(Collectors.toMap(PushGoodsInveroyVo::getSquareItemId, PushGoodsInveroyVo::g