Java8?Stream之groupingBy分組使用解讀
更新時間：2023年04月26日 08:35:49 作者：Archie_java
這篇文章主要介紹了Java8?Stream之groupingBy分組使用，具有很好的參考價值，希望對大家有所幫助。如有錯誤或未考慮完全的地方，望不吝賜教
Java8 Stream之groupingBy分組
本文主要講解：Java 8 Stream之Collectors.groupingBy()分組示例
Collectors.groupingBy()分組之常見用法
功能代碼：
?? ?/**
?? ? * 使用java8 stream groupingBy操作,按城市分組list
?? ? */
?? ?public void groupingByCity() {
?? ??? ?Map<String, List<Employee>> map = employees.stream().collect(Collectors.groupingBy(Employee::getCity));
?
?? ??? ?map.forEach((k, v) -> {
?? ??? ??? ?System.out.println(k + " = " + v);
?? ??? ?});
?? ?}
Collectors.groupingBy() 分組之統(tǒng)計每個分組的count
功能代碼：
?? ?/**
?? ? * 使用java8 stream groupingBy操作,按城市分組list統(tǒng)計count
?? ? */
?? ?public void groupingByCount() {
?? ??? ?Map<String, Long> map = employees.stream()
?? ??? ??? ??? ?.collect(Collectors.groupingBy(Employee::getCity, Collectors.counting()));
?
?? ??? ?map.forEach((k, v) -> {
?? ??? ??? ?System.out.println(k + " = " + v);
?? ??? ?});
?? ?}Collectors.groupingBy() 分組之統(tǒng)計分組平均值
功能代碼：
?? ?/**
?? ? * 使用java8 stream groupingBy操作,按城市分組list并計算分組年齡平均值
?? ? */
?? ?public void groupingByAverage() {
?? ??? ?Map<String, Double> map = employees.stream()
?? ??? ??? ??? ?.collect(Collectors.groupingBy(Employee::getCity, Collectors.averagingInt(Employee::getAge)));
?
?? ??? ?map.forEach((k, v) -> {
?? ??? ??? ?System.out.println(k + " = " + v);
?? ??? ?});
?? ?}
Collectors.groupingBy() 分組之統(tǒng)計分組總值
功能代碼：
/**
?? ? * 使用java8 stream groupingBy操作,按城市分組list并計算分組銷售總值
?? ? */
?? ?public void groupingBySum() {
?? ??? ?Map<String, Long> map = employees.stream()
?? ??? ??? ??? ?.collect(Collectors.groupingBy(Employee::getCity, Collectors.summingLong(Employee::getAmount)));
?
?? ??? ?map.forEach((k, v) -> {
?? ??? ??? ?System.out.println(k + " = " + v);
?? ??? ?});
?
?? ??? ?// 對Map按照分組銷售總值逆序排序
?? ??? ?Map<String, Long> sortedMap = new LinkedHashMap<>();
?? ??? ?map.entrySet().stream().sorted(Map.Entry.<String, Long> comparingByValue().reversed())
?? ??? ??? ??? ?.forEachOrdered(e -> sortedMap.put(e.getKey(), e.getValue()));
?
?? ??? ?sortedMap.forEach((k, v) -> {
?? ??? ??? ?System.out.println(k + " = " + v);
?? ??? ?});
?? ?}Collectors.groupingBy() 分組之Join分組List
功能代碼：
/**
?? ? * 使用java8 stream groupingBy操作,按城市分組list并通過join操作連接分組list中的對象的name 屬性使用逗號分隔
?? ? */
?? ?public void groupingByString() {
?? ??? ?Map<String, String> map = employees.stream().collect(Collectors.groupingBy(Employee::getCity,
?? ??? ??? ??? ?Collectors.mapping(Employee::getName, Collectors.joining(", ", "Names: [", "]"))));
?
?? ??? ?map.forEach((k, v) -> {
?? ??? ??? ?System.out.println(k + " = " + v);
?? ??? ?});
?? ?}Collectors.groupingBy() 分組之轉(zhuǎn)換分組結(jié)果List -> List
功能代碼：
/**
?? ? * 使用java8 stream groupingBy操作,按城市分組list,將List轉(zhuǎn)化為name的List
?? ? */
?? ?public void groupingByList() {
?? ??? ?Map<String, List<String>> map = employees.stream().collect(
?? ??? ??? ??? ?Collectors.groupingBy(Employee::getCity, Collectors.mapping(Employee::getName, Collectors.toList())));
?
?? ??? ?map.forEach((k, v) -> {
?? ??? ??? ?System.out.println(k + " = " + v);
?? ??? ??? ?v.stream().forEach(item -> {
?? ??? ??? ??? ?System.out.println("item = " + item);
?? ??? ??? ?});
?? ??? ?});
?? ?}Collectors.groupingBy() 分組之轉(zhuǎn)換分組結(jié)果List -> Set
功能代碼：
?? ?/**
?? ? * 使用java8 stream groupingBy操作,按城市分組list,將List轉(zhuǎn)化為name的Set
?? ? */
?? ?public void groupingBySet() {
?? ??? ?Map<String, Set<String>> map = employees.stream().collect(
?? ??? ??? ??? ?Collectors.groupingBy(Employee::getCity, Collectors.mapping(Employee::getName, Collectors.toSet())));
?
?? ??? ?map.forEach((k, v) -> {
?? ??? ??? ?System.out.println(k + " = " + v);
?? ??? ??? ?v.stream().forEach(item -> {
?? ??? ??? ??? ?System.out.println("item = " + item);
?? ??? ??? ?});
?? ??? ?});
?? ?}Collectors.groupingBy() 分組之使用對象分組List
功能代碼：
?? ?/**
?? ? * 使用java8 stream groupingBy操作,通過Object對象的成員分組List
?? ? */
?? ?public void groupingByObject() {
?? ??? ?Map<Manage, List<Employee>> map = employees.stream().collect(Collectors.groupingBy(item -> {
?? ??? ??? ?return new Manage(item.getName());
?? ??? ?}));
?
?? ??? ?map.forEach((k, v) -> {
?? ??? ??? ?System.out.println(k + " = " + v);
?? ??? ?});
?? ?}Collectors.groupingBy() 分組之使用兩個成員分組List
功能代碼：
?? ?/**
?? ? * 使用java8 stream groupingBy操作, 基于city 和name 實現(xiàn)多次分組
?? ? */
?? ?public void groupingBys() {
?? ??? ?Map<String, Map<String, List<Employee>>> map = employees.stream()
?? ??? ??? ??? ?.collect(Collectors.groupingBy(Employee::getCity, Collectors.groupingBy(Employee::getName)));
?
?? ??? ?map.forEach((k, v) -> {
?? ??? ??? ?System.out.println(k + " = " + v);
?? ??? ??? ?v.forEach((i, j) -> {
?? ??? ??? ??? ?System.out.println(i + " = " + j);
?? ??? ??? ?});
?? ??? ?});
?? ?}自定義Distinct對結(jié)果去重
功能代碼
/**
?? ? * 使用java8 stream groupingBy操作, 基于Distinct 去重數(shù)據(jù)
?? ? */
?? ?public void groupingByDistinct() {
?? ??? ?List<Employee> list = employees.stream().filter(distinctByKey(Employee :: getCity))
?? ??? ??? ??? ?.collect(Collectors.toList());;
?
?? ??? ?list.stream().forEach(item->{
?? ??? ??? ?System.out.println("city = " + item.getCity());
?? ??? ?});
?? ??? ?
?? ??? ?
?? ?}
?
?? ?/**
?? ? * 自定義重復key 規(guī)則
?? ? * @param keyExtractor
?? ? * @return
?? ? */
?? ?private static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) {
?? ??? ?Set<Object> seen = ConcurrentHashMap.newKeySet();
?? ??? ?return t -> seen.add(keyExtractor.apply(t));
?? ?}完整源代碼：
package com.stream;
?
import java.util.ArrayList;
import java.util.Arrays;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Random;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Collectors;
?
/**
?* Java 8 Stream 之groupingBy 分組講解
?*?
?* @author zzg
?*
?*/
public class Java8GroupBy {
?
?? ?List<Employee> employees = new ArrayList<Employee>();
?
?? ?/**
?? ? * 數(shù)據(jù)初始化
?? ? */
?? ?public void init() {
?? ??? ?List<String> citys = Arrays.asList("湖南", "湖北", "江西", "廣西 ");
?? ??? ?for (int i = 0; i < 10; i++) {
?? ??? ??? ?Random random = new Random();
?? ??? ??? ?Integer index = random.nextInt(4);
?? ??? ??? ?Employee employee = new Employee(citys.get(index), "姓名" + i, (random.nextInt(4) * 10 - random.nextInt(4)),
?? ??? ??? ??? ??? ?(random.nextInt(4) * 1000 - random.nextInt(4)));
?? ??? ??? ?employees.add(employee);
?? ??? ?}
?? ?}
?
?? ?/**
?? ? * 使用java8 stream groupingBy操作,按城市分組list
?? ? */
?? ?public void groupingByCity() {
?? ??? ?Map<String, List<Employee>> map = employees.stream().collect(Collectors.groupingBy(Employee::getCity));
?
?? ??? ?map.forEach((k, v) -> {
?? ??? ??? ?System.out.println(k + " = " + v);
?? ??? ?});
?? ?}
?
?? ?/**
?? ? * 使用java8 stream groupingBy操作,按城市分組list統(tǒng)計count
?? ? */
?? ?public void groupingByCount() {
?? ??? ?Map<String, Long> map = employees.stream()
?? ??? ??? ??? ?.collect(Collectors.groupingBy(Employee::getCity, Collectors.counting()));
?
?? ??? ?map.forEach((k, v) -> {
?? ??? ??? ?System.out.println(k + " = " + v);
?? ??? ?});
?? ?}
?
?? ?/**
?? ? * 使用java8 stream groupingBy操作,按城市分組list并計算分組年齡平均值
?? ? */
?? ?public void groupingByAverage() {
?? ??? ?Map<String, Double> map = employees.stream()
?? ??? ??? ??? ?.collect(Collectors.groupingBy(Employee::getCity, Collectors.averagingInt(Employee::getAge)));
?
?? ??? ?map.forEach((k, v) -> {
?? ??? ??? ?System.out.println(k + " = " + v);
?? ??? ?});
?? ?}
?
?? ?/**
?? ? * 使用java8 stream groupingBy操作,按城市分組list并計算分組銷售總值
?? ? */
?? ?public void groupingBySum() {
?? ??? ?Map<String, Long> map = employees.stream()
?? ??? ??? ??? ?.collect(Collectors.groupingBy(Employee::getCity, Collectors.summingLong(Employee::getAmount)));
?
?? ??? ?map.forEach((k, v) -> {
?? ??? ??? ?System.out.println(k + " = " + v);
?? ??? ?});
?
?? ??? ?// 對Map按照分組銷售總值逆序排序
?? ??? ?Map<String, Long> sortedMap = new LinkedHashMap<>();
?? ??? ?map.entrySet().stream().sorted(Map.Entry.<String, Long> comparingByValue().reversed())
?? ??? ??? ??? ?.forEachOrdered(e -> sortedMap.put(e.getKey(), e.getValue()));
?
?? ??? ?sortedMap.forEach((k, v) -> {
?? ??? ??? ?System.out.println(k + " = " + v);
?? ??? ?});
?? ?}
?
?? ?/**
?? ? * 使用java8 stream groupingBy操作,按城市分組list并通過join操作連接分組list中的對象的name 屬性使用逗號分隔
?? ? */
?? ?public void groupingByString() {
?? ??? ?Map<String, String> map = employees.stream().collect(Collectors.groupingBy(Employee::getCity,
?? ??? ??? ??? ?Collectors.mapping(Employee::getName, Collectors.joining(", ", "Names: [", "]"))));
?
?? ??? ?map.forEach((k, v) -> {
?? ??? ??? ?System.out.println(k + " = " + v);
?? ??? ?});
?? ?}
?
?? ?/**
?? ? * 使用java8 stream groupingBy操作,按城市分組list,將List轉(zhuǎn)化為name的List
?? ? */
?? ?public void groupingByList() {
?? ??? ?Map<String, List<String>> map = employees.stream().collect(
?? ??? ??? ??? ?Collectors.groupingBy(Employee::getCity, Collectors.mapping(Employee::getName, Collectors.toList())));
?
?? ??? ?map.forEach((k, v) -> {
?? ??? ??? ?System.out.println(k + " = " + v);
?? ??? ??? ?v.stream().forEach(item -> {
?? ??? ??? ??? ?System.out.println("item = " + item);
?? ??? ??? ?});
?? ??? ?});
?? ?}
?
?? ?/**
?? ? * 使用java8 stream groupingBy操作,按城市分組list,將List轉(zhuǎn)化為name的Set
?? ? */
?? ?public void groupingBySet() {
?? ??? ?Map<String, Set<String>> map = employees.stream().collect(
?? ??? ??? ??? ?Collectors.groupingBy(Employee::getCity, Collectors.mapping(Employee::getName, Collectors.toSet())));
?
?? ??? ?map.forEach((k, v) -> {
?? ??? ??? ?System.out.println(k + " = " + v);
?? ??? ??? ?v.stream().forEach(item -> {
?? ??? ??? ??? ?System.out.println("item = " + item);
?? ??? ??? ?});
?? ??? ?});
?? ?}
?
?? ?/**
?? ? * 使用java8 stream groupingBy操作,通過Object對象的成員分組List
?? ? */
?? ?public void groupingByObject() {
?? ??? ?Map<Manage, List<Employee>> map = employees.stream().collect(Collectors.groupingBy(item -> {
?? ??? ??? ?return new Manage(item.getName());
?? ??? ?}));
?
?? ??? ?map.forEach((k, v) -> {
?? ??? ??? ?System.out.println(k + " = " + v);
?? ??? ?});
?? ?}
?
?? ?/**
?? ? * 使用java8 stream groupingBy操作, 基于city 和name 實現(xiàn)多次分組
?? ? */
?? ?public void groupingBys() {
?? ??? ?Map<String, Map<String, List<Employee>>> map = employees.stream()
?? ??? ??? ??? ?.collect(Collectors.groupingBy(Employee::getCity, Collectors.groupingBy(Employee::getName)));
?
?? ??? ?map.forEach((k, v) -> {
?? ??? ??? ?System.out.println(k + " = " + v);
?? ??? ??? ?v.forEach((i, j) -> {
?? ??? ??? ??? ?System.out.println(i + " = " + j);
?? ??? ??? ?});
?? ??? ?});
?? ?}
?
?? ?/**
?? ? * 使用java8 stream groupingBy操作, 基于Distinct 去重數(shù)據(jù)
?? ? */
?? ?public void groupingByDistinct() {
?? ??? ?List<Employee> list = employees.stream().filter(distinctByKey(Employee :: getCity))
?? ??? ??? ??? ?.collect(Collectors.toList());;
?
?? ??? ?list.stream().forEach(item->{
?? ??? ??? ?System.out.println("city = " + item.getCity());
?? ??? ?});
?? ??? ?
?? ??? ?
?? ?}
?
?? ?/**
?? ? * 自定義重復key 規(guī)則
?? ? * @param keyExtractor
?? ? * @return
?? ? */
?? ?private static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) {
?? ??? ?Set<Object> seen = ConcurrentHashMap.newKeySet();
?? ??? ?return t -> seen.add(keyExtractor.apply(t));
?? ?}
?
?? ?public static void main(String[] args) {
?? ??? ?// TODO Auto-generated method stub
?? ??? ?Java8GroupBy instance = new Java8GroupBy();
?? ??? ?instance.init();
?? ??? ?instance.groupingByCity();
?? ??? ?instance.groupingByCount();
?? ??? ?instance.groupingByAverage();
?? ??? ?instance.groupingBySum();
?? ??? ?instance.groupingByString();
?? ??? ?instance.groupingByList();
?? ??? ?instance.groupingBySet();
?? ??? ?instance.groupingByObject();
?? ??? ?instance.groupingBys();
?? ??? ?instance.groupingByDistinct();
?
?? ?}
?
?? ?class Employee {
?? ??? ?private String city;
?? ??? ?private String name;
?? ??? ?private Integer age;
?? ??? ?private Integer amount;
?
?? ??? ?public String getCity() {
?? ??? ??? ?return city;
?? ??? ?}
?
?? ??? ?public void setCity(String city) {
?? ??? ??? ?this.city = city;
?? ??? ?}
?
?? ??? ?public String getName() {
?? ??? ??? ?return name;
?? ??? ?}
?
?? ??? ?public void setName(String name) {
?? ??? ??? ?this.name = name;
?? ??? ?}
?
?? ??? ?public Integer getAge() {
?? ??? ??? ?return age;
?? ??? ?}
?
?? ??? ?public void setAge(Integer age) {
?? ??? ??? ?this.age = age;
?? ??? ?}
?
?? ??? ?public Integer getAmount() {
?? ??? ??? ?return amount;
?? ??? ?}
?
?? ??? ?public void setAmount(Integer amount) {
?? ??? ??? ?this.amount = amount;
?? ??? ?}
?
?? ??? ?public Employee(String city, String name, Integer age, Integer amount) {
?? ??? ??? ?super();
?? ??? ??? ?this.city = city;
?? ??? ??? ?this.name = name;
?? ??? ??? ?this.age = age;
?? ??? ??? ?this.amount = amount;
?? ??? ?}
?
?? ??? ?public Employee() {
?? ??? ??? ?super();
?? ??? ?}
?? ?}
?
?? ?class Manage {
?? ??? ?private String name;
?
?? ??? ?public String getName() {
?? ??? ??? ?return name;
?? ??? ?}
?
?? ??? ?public void setName(String name) {
?? ??? ??? ?this.name = name;
?? ??? ?}
?
?? ??? ?public Manage(String name) {
?? ??? ??? ?super();
?? ??? ??? ?this.name = name;
?? ??? ?}
?
?? ??? ?public Manage() {
?? ??? ??? ?super();
?? ??? ?}
?? ?}
?
}總結(jié)
以上為個人經(jīng)驗，希望能給大家一個參考，也希望大家多多支持腳本之家。
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