list转map,Java Stream List<T> 转 Map<Field, Count>，统计List中对象属性出现次数，以Map返回

Java Stream List<T> 转 Map<Field, Count>，统计List中对象属性出现次数，以Map返回

主要通过 Collectors.counting() 来统计出现次数

List<FaAdmin> list = Lists.newArrayList();
list.add(new FaAdmin(100L, "a"));
list.add(new FaAdmin(101L, "b"));
list.add(new FaAdmin(102L, "c"));
list.add(new FaAdmin(100L, "e"));

Map<Long, Long> map = list.stream().collect(
        Collectors.groupingBy(FaAdmin::getId, Collectors.counting()));

System.out.println(map);