用java的stream流库在实际项目的使用案例

Dear 丶 2022-09-09 09:24 70阅读 0赞

由于自己用stream+lambda很不熟悉，用文章记录在一个电商项目中的用法  
购物车模块：

//获取购物车，校验（是否有商品、库存）
    		List<Cart> cartList = cartService.listForCart(uid).stream()
    				.filter(Cart::getProductSelected)
    				.collect(Collectors.toList());

订单模块：

//获取cartList里的productIds
    		Set<Integer> productIdSet = cartList.stream()
    				.map(Cart::getProductId)
    				.collect(Collectors.toSet());
    		List<Product> productList = productMapper.selectByProductIdSet(productIdSet);
    		Map<Integer, Product> map  = productList.stream()
    				.collect(Collectors.toMap(Product::getId, product -> product));
    					List<OrderItem> orderItemList = new ArrayList<>();
    		Long orderNo = generateOrderNo();
    		for (Cart cart : cartList) { 
    			//根据productId查数据库
    			Product product = map.get(cart.getProductId());
    			//是否有商品
    			if (product == null) { 
    				return ResponseVo.error(ResponseEnum.PRODUCT_NOT_EXIST,
    						"商品不存在. productId = " + cart.getProductId());
    			}
    			//商品上下架状态
    			if (!ProductStatusEnum.ON_SALE.getCode().equals(product.getStatus())) { 
    				return ResponseVo.error(ResponseEnum.PRODUCT_OFF_SALE_OR_DELETE,
    						"商品不是在售状态. " + product.getName());
    			}
    			}

返回订单视图

private OrderVo buildOrderVo(Order order, List<OrderItem> orderItemList, Shipping shipping) { 
    		OrderVo orderVo = new OrderVo();
    		BeanUtils.copyProperties(order, orderVo);
    
    		List<OrderItemVo> OrderItemVoList = orderItemList.stream().map(e -> { 
    			OrderItemVo orderItemVo = new OrderItemVo();
    			BeanUtils.copyProperties(e, orderItemVo);
    			return orderItemVo;
    		}).collect(Collectors.toList());
    		orderVo.setOrderItemVoList(OrderItemVoList);
    
    		if (shipping != null) { 
    			orderVo.setShippingId(shipping.getId());
    			orderVo.setShippingVo(shipping);
    		}
    
    		return orderVo;
    	}

创建订单

private Order buildOrder(Integer uid,
    							 Long orderNo,
    							 Integer shippingId,
    							 List<OrderItem> orderItemList
    							 ) { 
    		BigDecimal payment = orderItemList.stream()
    				.map(OrderItem::getTotalPrice)
    				.reduce(BigDecimal.ZERO, BigDecimal::add);
    
    		Order order = new Order();
    		order.setOrderNo(orderNo);
    		order.setUserId(uid);
    		order.setShippingId(shippingId);
    		order.setPayment(payment);
    		order.setPaymentType(PaymentTypeEnum.PAY_ONLINE.getCode());
    		order.setPostage(0);
    		order.setStatus(OrderStatusEnum.NO_PAY.getCode());
    		return order;
    	}

获取订单列表

@Override
    	public ResponseVo<PageInfo> list(Integer uid, Integer pageNum, Integer pageSize) { 
    		PageHelper.startPage(pageNum, pageSize);
    		List<Order> orderList = orderMapper.selectByUid(uid);
    
    		Set<Long> orderNoSet = orderList.stream()
    				.map(Order::getOrderNo)
    				.collect(Collectors.toSet());
    		List<OrderItem> orderItemList = orderItemMapper.selectByOrderNoSet(orderNoSet);
    		Map<Long, List<OrderItem>> orderItemMap = orderItemList.stream()
    				.collect(Collectors.groupingBy(OrderItem::getOrderNo));
    
    		Set<Integer> shippingIdSet = orderList.stream()
    				.map(Order::getShippingId)
    				.collect(Collectors.toSet());
    		List<Shipping> shippingList = shippingMapper.selectByIdSet(shippingIdSet);
    		Map<Integer, Shipping> shippingMap = shippingList.stream()
    				.collect(Collectors.toMap(Shipping::getId, shipping -> shipping));
    
    		List<OrderVo> orderVoList = new ArrayList<>();
    		for (Order order : orderList) { 
    			OrderVo orderVo = buildOrderVo(order,
    					orderItemMap.get(order.getOrderNo()),
    					shippingMap.get(order.getShippingId()));
    			orderVoList.add(orderVo);
    		}
    		PageInfo pageInfo = new PageInfo<>(orderList);
    		pageInfo.setList(orderVoList);
    
    		return ResponseVo.success(pageInfo);
    	}

关于Collectors.groupingBy：根据一个或多个属性对集合中的项目进行分组，返回一个map:

Map<Integer, List<Integer>> mapGroupBy = Stream.of(1, 2, 3, 4, 5, 4, 3).collect(Collectors.groupingBy(x -> x * 10));
    System.out.println(mapGroupBy); // {50=[5], 20=[2], 40=[4, 4], 10=[1], 30=[3, 3]}
    for(Map.Entry entry:mapGroupBy.entrySet())
    { 
        System.out.print(entry.getKey()+":");
        System.out.println(String.valueOf(entry.getValue()));
    }

![在这里插入图片描述][57085badeb594929a587df8e226ff2ce.png]

[57085badeb594929a587df8e226ff2ce.png]: /images/20220829/b62cf6c04e9245e9a8ac75b8ceb7bda6.png