使用Stream排序分组
一、 集合排序
package com.xiaobu.sort;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;
/**
* @author xiaobu
* @version JDK1.8.0_171
* @date on 2019/6/24 22:17
* @description V1.0 sorted(Comparator.reverseOrder()) 逆序 默认是正序
*/
public class SortDemo1 {
public static void main(String[] args) {
sortAsc();
sortDesc();
}
/**
* @author xiaobu
* @date 2019/6/24 22:31
* @return void
* @descprition 正序排列
* @version 1.0
*/
public static void sortAsc(){
List<Integer> list = new ArrayList<>();
list.add(50);
list.add(45);
list.add(25);
list.add(98);
list.add(32);
List<Integer> collect = list.stream().sorted().collect(Collectors.toList());
System.out.println("list元素正序：" + collect);
}
/**
* @author xiaobu
* @date 2019/6/24 22:31
* @return void
* @descprition 逆序排列
* @version 1.0
*/
public static void sortDesc(){
List<Integer> list = new ArrayList<>();
list.add(50);
list.add(45);
list.add(25);
list.add(98);
list.add(32);
List<Integer> collect = list.stream().sorted(Comparator.reverseOrder()).collect(Collectors.toList());
System.out.println("list元素逆序：" + collect);
}
}
二、根据某个属性排序
package com.xiaobu.sort;
import lombok.Data;
import java.math.BigDecimal;
/**
* @author xiaobu
* @version JDK1.8.0_171
* @date on 2019/6/24 22:03
* @description V1.0
*/
@Data
public class Person {
private String name;
private BigDecimal salary;
public Person(){}
public Person(String name,BigDecimal salary){
this. name = name;
this.salary =salary;
}
}
package com.xiaobu.sort;
import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;
/**
* @author xiaobu
* @version JDK1.8.0_171
* @date on 2019/6/24 22:02
* @description V1.0 Comparator.comparing()根据属性排序
*/
public class SortDemo {
public static void main(String[] args) {
Person p1 = new Person("张三", new BigDecimal("50.0"));
Person p2 = new Person("王五", new BigDecimal("25.0"));
Person p3 = new Person("李四", new BigDecimal("68.0"));
Person p4 = new Person("李四", new BigDecimal("17.0"));
Person p5 = new Person("张三", new BigDecimal("45.0"));
List<Person> list = new ArrayList<>();
list.add(p1);
list.add(p2);
list.add(p3);
list.add(p4);
list.add(p5);
sortAsc(list);
sortDesc(list);
}
/**
* @author xiaobu
* @date 2019/6/24 22:46
* @param list List
* @return void
* @descprition
* @version 1.0
*/
public static void sortAsc(List<Person> list){
List<Person> collect = list.stream().sorted(Comparator.comparing(Person::getSalary).reversed()).collect(Collectors.toList());
System.out.println("元素的属性值倒序："+collect);
}
/**
* @author xiaobu
* @date 2019/6/24 22:46
* @param list List
* @return void
* @descprition
* @version 1.0
*/
public static void sortDesc(List<Person> list){
List<Person> collect=list.stream().sorted(Comparator.comparing(Person::getSalary)).collect(Collectors.toList());
System.out.println("元素的属性值倒序："+collect);
}
}
三、分组排序
package com.xiaobu.demo;
import lombok.Data;
/**
* @author xiaobu
* @version JDK1.8.0_171
* @date on 2021/6/23 21:25
* @description
*/
@Data
public class Person {
private String name;
private Integer age;
}
package com.xiaobu.demo;
import java.util.*;
import java.util.stream.Collectors;
/**
* @author xiaobu
* @version JDK1.8.0_171
* @date on 2021/6/22 20:53
* @description
*/
public class Demo1 {
public static void main(String[] args) {
testInteger();
testString();
test2();
groupByTest();
}
public static void testInteger() {
List<Map<String, Integer>> list = new ArrayList<>();
Map<String, Integer> map1 = new HashMap<>(16);
map1.put("id", 1);
map1.put("age", 1);
Map<String, Integer> map2 = new HashMap<>(16);
map2.put("id", 1);
map2.put("age", 1);
Map<String, Integer> map3 = new HashMap<>(16);
map3.put("id", 2);
map3.put("age", 1);
list.add(map1);
list.add(map2);
list.add(map3);
LinkedHashMap<Integer, List<Map<String, Integer>>> integerMap = list.stream()
.sorted(Comparator.comparingInt(map -> (Integer) map.get("id")))
.collect(Collectors.groupingBy(map -> (Integer) map.get("id"), LinkedHashMap::new, Collectors.toList()));
//正常输出
System.out.println("integerMap = " + integerMap);
}
public static void testString() {
List<Map<String, String>> list = new ArrayList<>();
Map<String, String> map1 = new HashMap<>(16);
map1.put("id", "1");
map1.put("age", "1");
Map<String, String> map2 = new HashMap<>(16);
map2.put("id", "1");
map2.put("age", "1");
Map<String, String> map3 = new HashMap<>(16);
map3.put("id", "2");
map3.put("age", "1");
list.add(map1);
list.add(map2);
list.add(map3);
LinkedHashMap<String, List<Map<String, String>>> stringMap = list.stream()
.sorted(Comparator.comparing(map -> map.get("id")))
.collect(Collectors.groupingBy(map -> map.get("id"), LinkedHashMap::new, Collectors.toList()));
//正常输出
System.out.println("stringMap = " + stringMap);
}
public static void test2() {
List<Map<String, Object>> dataList = new ArrayList<>();
Map<String, Object> map1 = new HashMap<>(16);
map1.put("id", "1");
map1.put("name", "1");
Map<String, Object> map2 = new HashMap<>(16);
map2.put("id", "1");
map2.put("name", "2");
Map<String, Object> map3 = new HashMap<>(16);
map3.put("id", "2");
map3.put("name", "3");
dataList.add(map1);
dataList.add(map2);
dataList.add(map3);
Map<String, List<Map<String, Object>>> listLinkedHashMap = new LinkedHashMap<>();
Map<String, List<Map<String, Object>>> temp = dataList.stream().collect(Collectors.groupingBy(map -> (String) map.get("id")));
temp.entrySet().stream().sorted(Map.Entry.comparingByKey()).forEachOrdered(e -> listLinkedHashMap.put(e.getKey(), e.getValue()));
System.out.println("listLinkedHashMap = " + listLinkedHashMap);
//comparingInt和comparing 会报错 要明确的指定类型 Exception in thread "main" java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer
LinkedHashMap<Integer, List<Map<String, Object>>> ageMap = dataList.stream()
.sorted(Comparator.comparingInt(map -> (Integer) map.get("id")))
.collect(Collectors.groupingBy(map -> (Integer) map.get("id"), LinkedHashMap::new, Collectors.toList()));
System.out.println("ageMap = " + ageMap);
}
/**
* 分组
*/
private static void groupByTest() {
List<Person> persons = new ArrayList<>();
for (int i = 1; i <= 40; i++) {
Random r = new Random();
Person person = new Person();
person.setName("abel-" + i);
person.setAge(25 + r.nextInt(50));
persons.add(person);
}
//将list 排序，并按照排序后的结果进行有序分组 不会报错
LinkedHashMap<Integer, List<Person>> ageMap = persons.stream().sorted(Comparator.comparingInt(Person::getAge)).collect(Collectors.groupingBy(Person::getAge, LinkedHashMap::new, Collectors.toList()));
System.out.println("ageMap = " + ageMap);
}
}