java8 stream().collect() 各种数据结构使用方法

// user 对象
@Data
public class User{
    private int age;private String name;
}
List<User> list = Lists.newArrayList();Set<Integer> ageSet = list.stream().map(User::getAge).collect(Collectors.toSet()); List<Integer> ageList = list.stream().map(User::getAge).collect(Collectors.toList()); Map<String,Integer> nameToAgeMap = list.stream().collect(Collectors.toMap(User::getName,User::getAge));Map<Integer, List<String>> ageToNameListMap = list.stream().collect(Collectors.groupingBy(User::getAge, Collectors.mapping(User::getAge, Collectors.toList())));Map<String,User> nameToUserMap = list.stream().collect(Collectors.toMap(User::getName,user -> user));