java8-map操作實例

• 抽取集合對象屬性
  • 循環打印

    list.stream().map(Location::getId).forEach(System.out::println);
    

  • 屬性轉List集合

    List<String> skus = list.stream().map(Goods::getSku).collect(Collectors.toList());
    

• List轉set

  Set<String> kSet = keys.stream().map(k -> k).collect(Collectors.toSet());
  

• List轉map

  Map<String,InventoryAdjustment>  adjustments = list.stream()
                   .map(InventoryChange::getAdjustment).collect(Collectors.toList())
                   .stream().collect(Collectors.toMap(InventoryAdjustment::getCreatedAt, adjustment->adjustment,(key1, key2)->key1));
  

• List去重（distinct()）

  List<Integer> goodsIds = list.stream().map(OrderDetail::getGoodsId).distinct().collect(Collectors.toList());
  

• 內部操作數據

  List<MiddleRedisSkuStock> skuStockList = values.stream().filter(StringUtils::isNotBlank).map(
                      value -> JSON.parseObject(value, MiddleRedisSkuStock.class)
              ).collect(Collectors.toList());
  

• 數值計算
  • BigDecimal求和

    BigDecimal	amount = list.stream().map(OrderDetail::getAmount).reduce(BigDecimal.ZERO,BigDecimal::add);
    

  • Integert求和

    list.stream().mapToInt(SalesOrderDetail::getGoodsSum).sum();
    

  • 獲取集合屬性最小值

    	BigDecimal minUnitPrice = list.stream().map(GoodsSku::getUnitPrice).min((u1, u2)->u1.compareTo(u2)).get();