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java 8 lambda表达式对list进行分组

news 2025/10/22 8:49:36

java8的lambda表达式提供了一些方便list操作的方法，主要涵盖分组、过滤、求和、最值、排序、去重。跟之前的传统写法对比，能少写不少代码。
分组函数groupingBy()
分组函数示例：

 Map<String, List<Workers>> groupBySex = WorkersList.stream().filter(v->v.getName()!=null).collect(Collectors.groupingBy(Workers::getName));

从WorkersList中筛选出name不为空的数据，再对这些数据按照name进行分组，分组结果是一个map。

1.创建实体类

import java.math.BigDecimal;
import java.util.Date;
public class Workers {private Long id;//姓名private String name;//年龄private int age;//工号private String jobNumber;//性别private String sex;//入职日期private Date entryDate;//家庭成员数量private BigDecimal familyMemberQuantity;public Long getId() {return id;}public void setId(Long id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public String getJobNumber() {return jobNumber;}public void setJobNumber(String jobNumber) {this.jobNumber = jobNumber;}public String getSex() {return sex;}public void setSex(String sex) {this.sex = sex;}public Date getEntryDate() {return entryDate;}public void setEntryDate(Date entryDate) {this.entryDate = entryDate;}public BigDecimal getFamilyMemberQuantity() {return familyMemberQuantity;}public void setFamilyMemberQuantity(BigDecimal familyMemberQuantity) {this.familyMemberQuantity = familyMemberQuantity;}
}

2.分组

通过groupingBy可以分组指定字段

public class Application {public static void main(String[] args) {List<Workers> WorkersList = new ArrayList<>();Workers workers = new Workers();workers.setAge(23);workers.setName("jimmy");workers.setJobNumber("mk");Workers worker = new Workers();worker.setAge(19);worker.setName("gigi");worker.setJobNumber("mimi");WorkersList.add(workers);
//分组Map<String, List<Workers>> groupBySex = WorkersList.stream().filter(v->v.getName()!=null).collect(Collectors.groupingBy(Workers::getName));//遍历分组for (Map.Entry<String, List<Workers>> entryWorkers : groupBySex.entrySet()) {String key = entryWorkers.getKey();List<Workers> entryWorkersList = entryWorkers.getValue();System.out.println(entryWorkersList);}}
}