java8 groupingby 二次处理数据
范例
Map<String, Set> prodMap =
prodList.stream().collect(Collectors.groupingBy(Product::getCategory, Collectors.mapping(Product::getName, Collectors.toList())));
范例
Map<String, Set> prodMap =
prodList.stream().collect(Collectors.groupingBy(Product::getCategory, Collectors.mapping(Product::getName, Collectors.toList())));