【Java】将查出来的List数据转换为嵌套的Map格式

public HashMap<String, HashMap<String, List<GoodsShoppingCart>>> getCartGoods() {
　　//查出来的数据
    List<GoodsShoppingCart> goodsShoppingCartList = goodsShoppingCartMapper.selectByUserId(UserSession.getUserId());
    HashMap<String, HashMap<String, List<GoodsShoppingCart>>> outMap = new HashMap<>(16);
    for (GoodsShoppingCart goodsShoppingCart : goodsShoppingCartList) {
        String planPurchaseId = goodsShoppingCart.getPlanPurchaseId();
        String cartCsDbid = goodsShoppingCart.getCartCsDbid();
        if (outMap.containsKey(planPurchaseId)) {
            if (outMap.get(planPurchaseId).containsKey(cartCsDbid)) {
                outMap.get(planPurchaseId).get(cartCsDbid).add(goodsShoppingCart);
            } else {
                outMap.get(planPurchaseId).put(cartCsDbid, new ArrayList<>());
                outMap.get(planPurchaseId).get(cartCsDbid).add(goodsShoppingCart);
            }
        } else {
            outMap.put(planPurchaseId, new HashMap<>(16));
            outMap.get(planPurchaseId).put(cartCsDbid, new ArrayList<>());
            outMap.get(planPurchaseId).get(cartCsDbid).add(goodsShoppingCart);
        }
    }
或者用三次foreach循环。

for (GoodsShoppingCart goodsShoppingCart : goodsShoppingCartList) {
        String planPurchaseId = goodsShoppingCart.getPlanPurchaseId();
        String cartCsDbid = goodsShoppingCart.getCartCsDbid();

outMap.put(planPurchaseId, new HashMap<>(16));
}

for (GoodsShoppingCart goodsShoppingCart : goodsShoppingCartList) {
    String planPurchaseId = goodsShoppingCart.getPlanPurchaseId();
    String cartCsDbid = goodsShoppingCart.getCartCsDbid();
    outMap.get(planPurchaseId).put(cartCsDbid, new ArrayList<>());
}
for (GoodsShoppingCart goodsShoppingCart : goodsShoppingCartList) {
    String planPurchaseId = goodsShoppingCart.getPlanPurchaseId();
    String cartCsDbid = goodsShoppingCart.getCartCsDbid();
    outMap.get(planPurchaseId).get(cartCsDbid).add(goodsShoppingCart);
}