這里博主給大家封裝好了一個(gè)工具類(lèi)，里面有兩個(gè)方法。
- 方法一：可以根據(jù)指定字段去除重復(fù)數(shù)據(jù)。
- 方法二：可以獲取到重復(fù)的數(shù)據(jù)。
大家在使用過(guò)程中直接拷貝下方代碼在要去重的類(lèi)中調(diào)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;
/**
* 操作去重工具類(lèi)
* @author mengzhichao
* @create 2022-11-02-15:15
*/
public class DeduplicationUtil {
/**
* 自定義函數(shù)去重（采用 Predicate函數(shù)式判斷，采用 Function獲取比較key）
* 內(nèi)部維護(hù)一個(gè) ConcurrentHashMap，并采用 putIfAbsent特性實(shí)現(xiàn)
*
* @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;
}
/**
* 只獲取重復(fù)的數(shù)據(jù)
*
* @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;
}
}
導(dǎo)入這個(gè)工具類(lèi)后怎么使用呢？我們接著往下看。
方法一根據(jù)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("張三");
list.add(student);
Student student2 =new Student();
student2.setId("1");
student2.setName("張三");
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l(fā)ist有幾條數(shù)據(jù)："+list.size());
List<Student> rstList = list.stream().filter(DeduplicationUtil.distinctByKey(Student::getId)).collect(Collectors.toList());
System.out.println("未去重前l(fā)ist有幾條數(shù)據(jù)："+rstList.size());
}
}
List rstList = list.stream().filter(DeduplicationUtil.distinctByKey(Student::getId)).collect(Collectors.toList());
- 這段代碼的意思是通過(guò)stream的filter方法進(jìn)行過(guò)濾，過(guò)濾Id不相同的數(shù)據(jù)并通過(guò)collect方法收集為一個(gè)新的集合。
代碼運(yùn)行結(jié)果文章來(lái)源：http://www.zghlxwxcb.cn/news/detail-602321.html
方法二獲取重復(fù)數(shù)據(jù)
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("張三");
list.add(student);
Student student2 =new Student();
student2.setId("1");
student2.setName("張三");
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("集合中的全部數(shù)據(jù)");
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("集合中的重復(fù)數(shù)據(jù)");
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());
- 這個(gè)和上面那個(gè)方法原理一樣的只是換了一個(gè)調(diào)用方法而已。
代碼運(yùn)行結(jié)果
文章來(lái)源地址http://www.zghlxwxcb.cn/news/detail-602321.html
到了這里，關(guān)于Java通過(guò)Lambda表達(dá)式根據(jù)指定字段去除重復(fù)數(shù)據(jù)（集合去重）的文章就介紹完了。如果您還想了解更多內(nèi)容，請(qǐng)?jiān)谟疑辖撬阉鱐OY模板網(wǎng)以前的文章或繼續(xù)瀏覽下面的相關(guān)文章，希望大家以后多多支持TOY模板網(wǎng)！
