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
