java8-collect操作实例

比眉伴天荒 2023-06-29 12:59 25阅读 0赞

*  集合分组（根基对象某属性）
    
        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()));
 *  计算集合中某属性的和
    
        list.stream().collect(Collectors.summingInt(OrderDetail::getGoodsSum)).intValue();
 *  List转Map(key重复时取第一个对象)
    
     *  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))));
 *  将对象的某两个属性作为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