如何使用Java 8流和Lambda将FlatMap分组

您可以尝试类似：

Map<String, List<Product>> res = operations.parallelStream().filter(s -> s.getTotal() > 10)    .collect(groupingBy(Selling::getClientName, mapping(Selling::getProducts,        Collector.of(ArrayList::new, List::addAll, (x, y) -> { x.addAll(y); return x;        }))));