java - 如何在java 8中按列表对象的多个参数进行分组并删除重复的行？

Question

这是我的代码:

public class User{
        private String id;
        private String userName;
        private Long birthDate;
        private String address;
        private boolean enabled;
        //Constructors
        // Getters && Setters
        ...
}

public class ServiceUser{
    List<User> users=new ArrayList<>();

    public ServiceUser(){
        users.add(new User("OPS","MESSI",15454222454L,"ADRESSE 1",true))
        users.add(new User("TA1","RICHARD",1245485456787L,"ADRESSE 1",true));
        users.add(new User("XA5","LANG",659854575424L,"ADRESSE 2",true));
        users.add(new User("DS7","RICHARD",1245485456787L,"ADRESSE 1",false));
        users.add(new User("OPD6","LONG",659854575424L,"ADRESSE 2",false));
        ...
    }

    protected List<User> getFiltredUsers(){
        // TODO here
    }
}

我想获得一个用户列表，例如:

User("OPS","MESSI",15454222454L,"ADRESSE 1",true)

如何删除具有相同用户名、出生日期、地址的所有重复行？

Nb: the user list is returned by the database, and just for the example i put it like that.

Answer 1

以下代码删除重复项并仅返回用户列表中不同的元素:

//used for grouping them by name, birthday and address
static Function<User, List<Object>> groupingComponent = user ->
Arrays.<Object>asList(user.getName(), user.getBirthday(),user.getAddress());
//grouping method used for grouping them by groupingComponent and frequency of it
private static Map<Object, Long> grouping(final List<User> users) {
    return users.stream()
            .collect(Collectors.groupingBy(groupingComponent, Collectors.counting()));
}
//filtering method used for filtering lists if element is contained more than 1 within a list
private static List<Object> filtering(final Map<Object, Long> map) {
    return map.keySet()
            .stream()
            .filter(key -> map.get(key) < 2)
            .collect(Collectors.toList());
}

简单的用法是:filtering(grouping(users));

System.out.println(filtering(grouping(users)));

<小时/>

更新3: 老实说，由于这三个参数(生日、姓名和地址)，这有点棘手。我现在能想到的最简单的方法是在 User 类中实现 hashCode 和 equals 方法(如果用户具有相同的三个值，则将用户标记为相同):

@Override
public int hashCode() {
    return (43 + 777);
}
@Override
public boolean equals(Object obj) {
    // checks to see whether the passed object is null, or if it’s typed as a 
    // different class. If it’s a different class then the objects are not equal.
    if (obj == null || getClass() != obj.getClass()) {
        return false;
    }
    // compares the objects’ fields.
    User user = (User) obj;
    return getName().contains(user.getName())
            && getBirthday() == user.getBirthday()
            && getAddress()== user.getAddress();
}

以及以下方法删除所有重复项

   public static List<User> filter(List<User> users) {
        Set<User> set = new HashSet<>();
        List<User> uniqueUsers = new ArrayList<>();
        List<User> doubleUsers = new ArrayList<>();
        Map<Boolean, List<User>> partitions = users.stream().collect(Collectors.partitioningBy(user -> set.add(user) == true));
        uniqueUsers.addAll(partitions.get(true));
        doubleUsers.addAll(partitions.get(false));
        uniqueUsers.removeAll(doubleUsers);
        return uniqueUsers;
    }