对List集合中对象的某一个属性进行去重排序

妖狐艹你老母 2022-01-22 06:21 354阅读 0赞

**引言:**  
    本文主要介绍通过JDK提供的原始的去重排序和使用Lambda表达式的形式进行集合中数据的去重和排序

**一.环境准备:**

1.实体类:

public class User {
        private Long id;
        private String name;
        public Long getId() {
            return id;
        }
        public void setId(Long id) {
            this.id = id;
        }
        public String getName() {
            return name;
        }
        public void setName(String name) {
            this.name = name;
        }
        public User() {
        }
        public User(Long id, String name) {
            this.id = id;
            this.name = name;
        }
        @Override
        public String toString() {
            return "User{" +
                    "id=" + id +
                    ", name='" + name + '\'' +
                    '}';
        }
    }

2.插入测试数据:

User u1 = new User(1L, "li");
    User u2 = new User(2L, "哈哈");
    User u3 = new User(1L, "li");
    User u4 = new User(2L, "li");
    List classList = new ArrayList();
    classList.add(u1);
    classList.add(u2);
    classList.add(u3);
    classList.add(u4);

**二.根据name属性值的Ascll码进行排序,没有去重:**

/**
     * 按照List中的某个String类型的属性进行排序
     *
     * @param list
     */
    
     Collections.sort(classList, new Comparator() {
         @Override
         public int compare(Object o1, Object o2) {
             User e1 = (User) o1;
             User e2 = (User) o2;
             return e1.getName().compareTo(e2.getName());
         }
     });
     classList.forEach( e -> System.out.println(e));

**三.通过name属性进行去重和重排序:**

Set<User> set = new TreeSet<User>(new Comparator<User>() {
           @Override
            public int compare(User o1, User o2) {
                return o1.getName().compareTo(o2.getName());
            }
        });
        set.addAll(classList);
    List<User> list = new ArrayList<>(set);
    list.forEach( e -> System.out.println(e));

**四.采用lambda进行去重和排序:**

List list1 = (List) classList.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(()->new TreeSet<>(Comparator.comparing(User::getName))), ArrayList::new));
          list1.forEach( e -> System.out.println(e));

**五.总结:**  
以上完成了对集合中的对象的属性进行去重和排序操作,使用lambda的方式显的代码少简单,但是不容易懂。