Java当中List集合根据对象某个属性进行去重

心已赠人 2024-03-23 12:18 103阅读 0赞

关于以下方法，直接可以在自己项目创建一个类，然后进行测试使用，去重方式有很多种，文本末尾也提供了每个方法的运行结果，供大家参考使用！

> 文章大量使用到了Java8当中的Lambda表达式，以及stream流相关基础知识。如果您用的不熟，没关系，可以直接复制下面的方案然后进行套着使用即可，如果想深入了解的，可以看一下这两篇文章：

Lambda讲解：[https://blog.csdn.net/weixin\_43888891/article/details/124795863][https_blog.csdn.net_weixin_43888891_article_details_124795863]  
Stream讲解：[https://blog.csdn.net/weixin\_43888891/article/details/124657128][https_blog.csdn.net_weixin_43888891_article_details_124657128]

测试对象：

@Data
    @AllArgsConstructor
    @ToString
    public class User {
        
        @ApiModelProperty("姓名")
        private String name;
    
        @ApiModelProperty("性别")
        private String gender;
    
        @ApiModelProperty("年龄")
        private Integer age;
    
        @ApiModelProperty("出生日期")
        private String birthday;
    
        @ApiModelProperty("证件类型")
        private String paperworkType;
    
        @ApiModelProperty("证件号码")
        private String identityNumber;
    }

import java.util.*;
    import java.util.concurrent.ConcurrentHashMap;
    import java.util.function.Function;
    import java.util.function.Predicate;
    import java.util.stream.Collectors;
    
    public class Test {
        
        private static final List<User> list = Arrays.asList(
                new User("张三", "男", 2, "2019-1-1", "身份证", "350781196403077840"),
                new User("李四", "男", 2, "2019-1-1", "港澳证", "350781196403077840"),
                new User("王五", "男", 9, "2019-1-1", "身份证", "350781196403077840"),
                new User("赵六", "男", 8, "2019-1-1", "身份证", "350781196403077840"),
                new User("赵六", "男", 8, "2019-1-1", "身份证", "350781196403077840"));
    
        /**
         * 对所有属性一样的数据进行去重
         */
        public static void allColumnDistinct() {
        
            List<User> collect = list.stream().distinct().collect(Collectors.toList());
            collect.forEach(System.out::println);
        }
    
        /**
         * 对单个属性去重，只返回去重的属性
         */
        public static void columnDistinct() {
        
            List<String> identityNumberList = list.stream().map(User::getIdentityNumber).distinct().collect(Collectors.toList());
            identityNumberList.forEach(System.out::println);
        }
    
        /**
         * 方式一：对单个属性一样的数据进行去重，下面是对身份证去重
         */
        public static void oneColumnDistinct1() {
        
            List<User> collect = list.stream().collect(Collectors.collectingAndThen(
                    Collectors.toCollection(() -> new TreeSet<>(
                            Comparator.comparing(User::getIdentityNumber))), ArrayList::new));
            collect.forEach(System.out::println);
        }
    
        /**
         * 多个字段条件去重
         */
        public static void twoColumnDistinct() {
        
            List<User> collect = list.stream().collect(Collectors.collectingAndThen(
                    Collectors.toCollection(() -> new TreeSet<>(
                            Comparator.comparing(p -> p.getIdentityNumber() + ";" + p.getPaperworkType()))), ArrayList::new));
            collect.forEach(System.out::println);
        }
    
        /**
         * 自定义属性判断
         *
         * @param keyExtractor
         * @param <T>
         * @return
         */
        public static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) {
        
            Map<Object, Boolean> seen = new ConcurrentHashMap<>(1);
            return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;
        }
    
        /**
         * 方式二：对单个属性一样的数据进行去重，下面是对身份证去重
         */
        public static void oneColumnDistinct2() {
        
            List<User> collect = list.stream().filter(distinctByKey(b -> b.getIdentityNumber())).collect(Collectors.toList());
            collect.forEach(System.out::println);
        }
    
        /**
         * 方式三：对单个属性一样的数据进行去重，下面是对身份证去重
         * 利用TreeSet进行去重
         */
        public static void oneColumnDistinct3() {
        
            TreeSet<User> collect = new TreeSet<>(Comparator.comparing(s -> s.getIdentityNumber()));
            list.forEach(a -> collect.add(a));
            collect.forEach(System.out::println);
        }
    
    
    	public static void main(String[] args) {
        
            System.out.println("-----------------allColumnDistinct---------------------");
            allColumnDistinct();
            System.out.println("-----------------columnDistinct---------------------");
            columnDistinct();
            System.out.println("-----------------oneColumnDistinct1---------------------");
            oneColumnDistinct1();
            System.out.println("-----------------twoColumnDistinct---------------------");
            twoColumnDistinct();
            System.out.println("-----------------oneColumnDistinct2---------------------");
            oneColumnDistinct2();
            System.out.println("-----------------oneColumnDistinct3---------------------");
            oneColumnDistinct3();
        }
    }

输出结果：

![在这里插入图片描述][1d5f1fd638834cc7a6285ec4dd19d599.png]

[https_blog.csdn.net_weixin_43888891_article_details_124795863]: https://blog.csdn.net/weixin_43888891/article/details/124795863
[https_blog.csdn.net_weixin_43888891_article_details_124657128]: https://blog.csdn.net/weixin_43888891/article/details/124657128
[1d5f1fd638834cc7a6285ec4dd19d599.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/23/a10874d23b494d1bad17abd83cec0fea.png