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

• 计算分组中某字段之和

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

• 获取分组后组的数量

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

• 计算分组后每组对象的数量

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

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

• 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))));
  

• 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