java8 stream将list分组并转换为对象某个属性的集合

Map<HttpMethod, Set<String>> whiteMap = list.stream().collect(Collectors.groupingBy(SecurityUrlBO::getMethod, Collectors.mapping(SecurityUrlBO::getUrl, Collectors.toSet())));

使用groupingBy时传递一个mapping参数，mapping到所需要取的对象值