第一:基础用法
package com.glch.test; import com.glch.base.util.StringUtil; import java.util.ArrayList; import java.util.List; import java.util.Set; import java.util.stream.Collectors; /** * @author zhongzhilong * @date 2021-03-25 * @description List的stream功能测试 */ public class ListStreamTest { public static void main(String[] args) { List<Animal> list = new ArrayList<>(); list.add(new Animal("小狗", 3, 1)); list.add(new Animal("小猫", 4, 0)); list.add(new Animal("小马", 5, 1)); // 获取所有动物的名称,并且转为List List<String> nameList = list.stream().map(Animal::getName).collect(Collectors.toList()); // 获取所有的动物名称,并且中间加入name不等于空的过滤,并且转为set Set<String> set = list.stream().filter(animal -> !StringUtil.isEmpty(animal.getName())).map(animal -> animal.getName()).collect(Collectors.toSet()); // 简洁版本 Set<String> set2 = list.stream().map(animal -> animal.getName()).collect(Collectors.toSet()); // 获取tag = 1的动物列表 List<Animal> tagList = list.stream().filter(animal -> animal.getTag() == 1).collect(Collectors.toList()); // 获取动物的总年龄之和 int sum = list.stream().mapToInt(Animal::getAge).sum(); // 对list按年龄降序查询 List<Animal> animalList = list.stream.sorted(Comparator.comparing(Animal::getAge).reversed()).collect(Collectors.toList()); // 对list按年龄升序查询 List<Animal> animalList = list.stream.sorted(Comparator.comparing(Animal::getAge)).collect(Collectors.toList()); // 1)list进行去重,2)按照年龄降序 3)排除标记为0的数据 List<Animal> reusltList = list.stream().filter(animal -> animal.getTag() != 0).sorted(Comparator.comparing(Animal::getAge).reversed()).distinct().collect(Collectors.toList()); } static class Animal { private String name; private Integer age; private Integer tag; public void setName(String name) { this.name = name; } public String getName() { return name; } public Integer getAge() { return age; } public Integer getTag() { return tag; } public void setTag(Integer tag) { this.tag = tag; } public void setAge(Integer age) { this.age = age; } public Animal(String name, Integer age, Integer tag) { this.name = name; this.age = age; this.tag = tag; } } }
第二:List<Map<String,Object>> 转List和String的方法
package liststream; import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; import java.util.stream.Collectors; /** * @author zhongzhilong * @date 2021/4/19 * @decription */ public class ListToStringTest { public static void main(String[] args) { List<Map<String, Object>> list = new ArrayList<>(); Map<String, Object> map = new HashMap<>(); map.put("name", "小明"); map.put("id", "1"); list.add(map); Map<String, Object> map2 = new HashMap<>(); map2.put("name", "小张"); map2.put("id", "2"); list.add(map2); // 1、List<Map<String,Object>>中获取List<String> List<String> stringList = list.stream().map(e -> e.get("id").toString()).collect(Collectors.toList()); stringList.forEach(e -> { System.out.print(e + " "); }); System.out.println("\n"); // 2、List<Map<String,Object>>中获取String String idString = list.stream().map(e -> e.get("id").toString()).collect(Collectors.joining(",")); System.out.println("idString = "+idString); } }
标签:Stream,name,stream,List,list,用法,public,Collectors From: https://www.cnblogs.com/liuyangjava/p/17141515.html