Java通过Lambda表达式根据指定字段去除重复数据（集合去重）

Posted 2023-02-15 剑桥大表哥

这里博主给大家封装好了一个工具类，里面有两个方法。

• 方法一：可以根据指定字段去除重复数据。
• 方法二：可以获取到重复的数据。

大家在使用过程中直接拷贝下方代码在要去重的类中调用即可。

package com.jzmy.specialist.entity.util;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Function;
import java.util.function.Predicate;

/**
 * 操作去重工具类
 * @author mengzhichao
 * @create 2022-11-02-15:15
 */
public class DeduplicationUtil 
    /**
     * 自定义函数去重（采用 Predicate函数式判断，采用 Function获取比较key）
     * 内部维护一个 ConcurrentHashMap，并采用 putIfAbsent特性实现
     *
     * @param keyExtractor
     * @param <T>
     * @return
     */
    public static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) 
        Map<Object,Boolean> seen = new ConcurrentHashMap<>();
        return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;
    

    /**
     * 只获取重复的数据
     *
     * @param keyExtractor
     * @param <T>
     * @return
     */
    public static <T> Predicate<T> distinctNotByKey(Function<? super T, ?> keyExtractor) 
        Map<Object,Boolean> seen = new ConcurrentHashMap<>();
        return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) != null;
    

导入这个工具类后怎么使用呢？我们接着往下看。

方法一根据指定字段去重

package com.jzmy.specialist.entity.util;

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

/**
 * @author mengzhichao
 * @create 2022-12-02-10:46
 */
public class Test 
    public static class Student

        private String id;

        private String name;

        public String getId() 
            return id;
        

        public void setId(String id) 
            this.id = id;
        

        public String getName() 
            return name;
        

        public void setName(String name) 
            this.name = name;
        
    

    public static void main(String[] args) 

        List<Student> list =new ArrayList<>();

        Student student =new Student();
        student.setId("1");
        student.setName("张三");
        list.add(student);

        Student student2 =new Student();
        student2.setId("1");
        student2.setName("张三");
        list.add(student2);

        Student student3 =new Student();
        student3.setId("1");
        student3.setName("李四");
        list.add(student3);

        Student student4 =new Student();
        student4.setId("2");
        student4.setName("王五");
        list.add(student4);

        System.out.println("未去重前list有几条数据："+list.size());


        List<Student> rstList = list.stream().filter(DeduplicationUtil.distinctByKey(Student::getId)).collect(Collectors.toList());

        System.out.println("未去重前list有几条数据："+rstList.size());
    

List rstList = list.stream().filter(DeduplicationUtil.distinctByKey(Student::getId)).collect(Collectors.toList());

• 这段代码的意思是通过stream的filter方法进行过滤，过滤Id不相同的数据并通过collect方法收集为一个新的集合。

代码运行结果

方法二获取重复数据

package com.jzmy.specialist.entity.util;

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

/**
 * @author mengzhichao
 * @create 2022-12-02-10:46
 */
public class Test 
    public static class Student

        private String id;

        private String name;

        public String getId() 
            return id;
        

        public void setId(String id) 
            this.id = id;
        

        public String getName() 
            return name;
        

        public void setName(String name) 
            this.name = name;
        
    

    public static void main(String[] args) 

        List<Student> list =new ArrayList<>();

        Student student =new Student();
        student.setId("1");
        student.setName("张三");
        list.add(student);

        Student student2 =new Student();
        student2.setId("1");
        student2.setName("张三");
        list.add(student2);

        Student student3 =new Student();
        student3.setId("1");
        student3.setName("李四");
        list.add(student3);

        Student student4 =new Student();
        student4.setId("2");
        student4.setName("王五");
        list.add(student4);

        System.out.println("集合中的全部数据");
        for (int i=0;i<list.size();i++)
            System.out.println(list.get(i).getId());
            System.out.println(list.get(i).getName());
        

        List<Student> rstList = list.stream().filter(DeduplicationUtil.distinctNotByKey(Student::getId)).collect(Collectors.toList());

        System.out.println("集合中的重复数据");
        for (int i=0;i<rstList.size();i++)
            System.out.println(rstList.get(i).getId());
            System.out.println(rstList.get(i).getName());
        
    

List rstList = list.stream().filter(DeduplicationUtil.distinctNotByKey(Student::getId)).collect(Collectors.toList());

• 这个和上面那个方法原理一样的只是换了一个调用方法而已。

代码运行结果