Question

遍历List之后，对每条数据再进行三级联动，怎么实现

Answer 1

List<Product> productList = Arrays.asList(
new Product("type1", "desc1", "brand1", "model1"),
new Product("type2", "desc2", "brand2", "model2"),
new Product("type3", "desc3", "brand3", "model3"),
new Product("type3", "desc5", "brand3", "model5"),
new Product("type4", "desc4", "brand4", "model4")
);

Map<String, Map<String,String>> productsMap =
productList.stream()
.collect(Collectors.groupingBy(Product::getType, // 第一层种类映射
Collectors.groupingBy(Product::getBrand, // 第二层品牌映射
Collectors.mapping(Product::getModel, Collectors.joining(", ")))));