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;
/**
* @author: rhyme
* @date: 2019-09-26 17:31
* @topic: "主题"
* @description: "描述"
*/
@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<People> 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;
/**
* @author: rhyme
* @date: 2019-10-14 15:59
* @topic: "主题"
* @description: "描述"
*/
public class GroupByTest {
private List<People> 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);
}
}
/**
* 根据性别分组
*/
@Test
public void groupBySex() {
result = people.stream().collect(
Collectors.groupingBy(People::getSex)
);
}
/**
* 分别统计不同性别各自的人数
*/
@Test
public void groupBySexCount() {
result = people.stream().collect(
Collectors.groupingBy(People::getSex, Collectors.counting()
));
}
/**
* 分别统计不同性别各自的name列表
*/
@Test
public void groupBySexName() {
result = people.stream().collect(
Collectors.groupingBy(
People::getSex,
Collectors.mapping(People::getName, Collectors.toSet())
));
}
}
