List list對象去重方法總結

List<T> list對象去重方法總結

 【去重方法總結】：（java8）

package com.caox.utils;

import com.caox.model.UserInfo;

import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Collectors;

import static java.util.Comparator.comparingLong;
import static java.util.stream.Collectors.collectingAndThen;
import static java.util.stream.Collectors.toCollection;

/**
 * @author : nazi
 * @version : 1.0
 * @date : 2019/7/5 17:54
 * 去重List<對象>
 */
public class ListObjectNoRepeatUtils {


    /**
     * 去重字符串重複
     * @param stringList  字符串List
     * @return            返回去重字符串
     */
    public static List<String> removeStringListDupli(List<String> stringList) {
        Set<String> set = new LinkedHashSet<>();
        set.addAll(stringList);
        stringList.clear();
        stringList.addAll(set);
        return stringList;
    }

    /**
     * 根據對象屬性去重  屬性：userId
     * @param persons
     * @return
     */
    public static List<UserInfo> removeDupliById(List<UserInfo> persons) {
        Set<UserInfo> personSet = new TreeSet<>((o1, o2) -> o1.getUserId().compareTo(o2.getUserId()));
        personSet.addAll(persons);
        return new ArrayList<>(personSet);
    }

    /**
     * 根據對象多個屬性去重 屬性：userId + userName
     * @param persons
     * @return
     */
    public static List<UserInfo> removeDupliByMorePro(List<UserInfo> persons){
        List<UserInfo> personList = persons.stream().collect(Collectors
                .collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(o -> {
                    // 根據useId和userName進行去重
                    return o.getUserId() + "," + o.getUsername() +"," + o.getAge();
                }))), ArrayList::new));
        return  personList;
    }

    /**
     * 根據對象單個屬性去重 屬性：userId
     * @param persons
     * @return
     */
    public static List<UserInfo> removeDupliByUserId(List<UserInfo> persons){
        List<UserInfo> unique = persons.stream().collect(
                collectingAndThen(
                        toCollection(() -> new TreeSet<>(comparingLong(UserInfo::getUserId))), ArrayList::new)
        );
        return unique;
    }

    /**
     * 根據對象單個屬性去重 屬性：userId
     * @param persons
     * @return
     */
    public static List<UserInfo> removeDupliByUserIdNew(List<UserInfo> persons){

        List<UserInfo> personList = new ArrayList<>();
         persons.stream().filter(distinctByKey(p -> p.getUserId()))
                .forEach(p -> personList.add(p));
         return personList;
    }

    /**
     * 根據key去重重複
     * @param keyExtractor key執行器
     * @param <T>          泛型
     * @return
     */
    public static <T> Predicate<T> distinctByKey(Function<? super T, Object> keyExtractor) {
        Map<Object, Boolean> map = new ConcurrentHashMap<>();
        return t -> map.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;
    }

}

【對應實體類】： 

package com.caox.model;

import lombok.Data;

import java.text.SimpleDateFormat;
import java.util.Date;

/**
 * @author : nazi
 * @version : 1.0
 * @date : 2019/6/5 14:27
 */
@Data
public class UserInfo {

    private Integer userId;
    private String username;
    private Date birthDate;
    private Integer age;
    private float fRate;
    private char ch;

    public Date getBirthDate() {
        return birthDate;
    }

    public String getBirthDatestr() {
        SimpleDateFormat formater = new SimpleDateFormat("yyyy-MM-dd");
        return formater.format(getBirthDate());
    }

    public UserInfo(Integer userId, String username, Date birthDate, Integer age, float fRate, char ch) {
        this.userId = userId;
        this.username = username;
        this.birthDate = birthDate;
        this.age = age;
        this.fRate = fRate;
        this.ch = ch;
    }

    public UserInfo(Integer userId, String username) {
        this.userId = userId;
        this.username = username;
    }

    public UserInfo(Integer userId, String username, Integer age) {
        this.userId = userId;
        this.username = username;
        this.age = age;
    }

    @Override
    public String toString() {
        return "UserInfo{" +
                "userId=" + userId +
                ", username='" + username + '\'' +
                ", birthDate=" + birthDate +
                ", age=" + age +
                ", fRate=" + fRate +
                ", ch=" + ch +
                '}';
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        UserInfo userInfo = (UserInfo) o;

        if (!userId.equals(userInfo.userId)) return false;
        return username.equals(userInfo.username);

    }

    @Override
    public int hashCode() {
        int result = userId.hashCode();
        result = 31 * result + username.hashCode();
        return result;
    }
}