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
