Java 8: Map of field to list of items

Question

Lets say I have a List<Person> Gathering and I want a Map<String, List<Person>>, mapping Person.surname to a List of Person:s that have the same surname. Is there a convenient way to do this using streams?

Answer 1

是的，使用Collectors.groupingBy(...)：

Map<String, List<Person>> personsBySurname = gathering.stream()
        .collect(Collectors.groupingBy(Person::get‌​Surname));