Java通过Lambda表达式根据指定字段去除重复数据（集合去重）

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;public class DeduplicationUtil {        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;    }        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;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;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

来源地址：https://blog.csdn.net/weixin_45692705/article/details/128144013