JAVA8 STREAM COLLECT GROUPBY分组实例解析

这篇文章主要介绍了JAVA8 STREAM COLLECT GROUPBY分组实例解析,文中通过示例代码介绍的非常详细，对大家的学习或者工作具有一定的参考学习价值,需要的朋友可以参考下

实体类People，有个返回list的buildPeopleList方法，方便测试。

import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;


@Data
@NoArgsConstructor
@AllArgsConstructor
@Builder
public class People {
  private String name;

  private String character;

  private String sex;

  private int age;

  public static People buildDefault() {
    return People.builder().name("LuoTianyan").character("optimistic").sex("female").age(24).build();
  }

  public static List buildPeopleList() {
    People p1 = People.builder().name("LuoTianyan").character("optimistic").sex("female").age(24).build();
    People p2 = People.builder().name("Zhang").character("optimistic").sex("female").age(23).build();
    People p3 = People.builder().name("Hu").character("shy").sex("female").age(25).build();
    People p4 = People.builder().name("Y").character("Righteous").sex("male").age(24).build();
    return new ArrayList<>(Arrays.asList(p1, p2, p3, p4));
  }
}

测试类GroupByTest，分别根据性别分组，统计各个性别人数，以及各个性别映射姓名。

import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import org.springframework.util.CollectionUtils;

import java.util.List;
import java.util.Map;
import java.util.function.BiConsumer;
import java.util.stream.Collectors;


public class GroupByTest {
  private List people;
  private BiConsumer soutKV;
  private Map result;

  @Before
  public void init() {
    people = People.buildPeopleList();
    soutKV = (k, v) -> System.out.println(k + ":" + v);
  }

  @After
  public void soutResult() {
    if (!CollectionUtils.isEmpty(result)) {
      result.forEach(soutKV);
    }
  }

  
  @Test
  public void groupBySex() {
    result = people.stream().collect(
 Collectors.groupingBy(People::getSex)
    );
  }

  
  @Test
  public void groupBySexCount() {
    result = people.stream().collect(
 Collectors.groupingBy(People::getSex, Collectors.counting()
 ));
  }

  
  @Test
  public void groupBySexName() {
    result = people.stream().collect(
 Collectors.groupingBy(
     People::getSex,
     Collectors.mapping(People::getName, Collectors.toSet())
 ));
  }


}

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持考高分网。