这段逻辑可以用 stream实现吗

Question

Map<Integer, List<Integer>> orderId_CommodityIdMap；
key => 订单id     value => 该订单id  对应商品id 的list

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Map<Integer, SimpleCommodity> commodityId_SimpleCommodityMap;
key => 商品id  value => 商品信息

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Map<Integer, List<SimpleCommodity>> orderId_SimpleCommodityMap;
key => 订单id  value => 该订单id 对应商品信息 的list

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要通过 前2个 推出第3 个

Map<Integer, List<SimpleCommodity>> orderId_SimpleCommodityMap = new HashMap<>();
for (Map.Entry<Integer, List<Integer>> entry : orderId_CommodityIdMap.entrySet()){
            List<Integer> cIdList = entry.getValue();
            List<SimpleCommodity> simpleCommodityList = new ArrayList<>();
            for (Integer cId : cIdList)
                simpleCommodityList.add(commodityId_SimpleCommodityMap.get(cId));
            orderId_SimpleCommodityMap.put(entry.getKey(),simpleCommodityList);
      }

这段逻辑可以用 stream实现吗

Answer 1

// 1. 把所有的 values  整合为一个list
Map<Integer, List<Integer>> listMap = new HashMap<>();
ArrayList<List<Integer>> lists = new ArrayList<>(listMap.values());

// 2. 根据1.2推出3,不知道是不是你想要的效果
Map<Integer, List<Integer>> orderId_CommodityIdMap = new HashedMap();
Map<Integer, SimpleCommodity> commodityId_SimpleCommodityMap = new HashedMap();
Map<Integer, List<SimpleCommodity>> orderId_SimpleCommodityMap = new HashedMap();
orderId_CommodityIdMap.forEach((Key,Value) -> {
    List<SimpleCommodity> simpleCommodity = new ArrayList();
    Value.stream().forEach(commodityId -> simpleCommodity.add(commodityId_SimpleCommodityMap.get(commodityId)));
    orderId_SimpleCommodityMap.put(Key,simpleCommodity);
});