使用Stream排序分组-白红宇

使用Stream排序分组

阅读量：4182 次

发布时间：2019-05-26

本文共 6949 字，大约阅读时间需要 23 分钟。

一、基础类型排序

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
   
     list = new ArrayList<>();        list.add(50);        list.add(45);        list.add(25);        list.add(98);        list.add(32);        List
    
      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
      
        list = new ArrayList<>();        list.add(50);        list.add(45);        list.add(25);        list.add(98);        list.add(32);        List
       
         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 */@Datapublic 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
   
     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
     
       list){
           List
      
        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
        
          list){ List
         
           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 */@Datapublic 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
    
     > list = new ArrayList<>();        Map
     
       map1 = new HashMap<>(16);        map1.put("id", 1);        map1.put("age", 1);        Map
      
        map2 = new HashMap<>(16);        map2.put("id", 1);        map2.put("age", 1);        Map
       
         map3 = new HashMap<>(16);        map3.put("id", 2);        map3.put("age", 1);        list.add(map1);        list.add(map2);        list.add(map3);        LinkedHashMap
        
         >> 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
         
          
           > list = new ArrayList<>(); Map
           
             map1 = new HashMap<>(16); map1.put("id", "1"); map1.put("age", "1"); Map
            
              map2 = new HashMap<>(16); map2.put("id", "1"); map2.put("age", "1"); Map
             
               map3 = new HashMap<>(16); map3.put("id", "2"); map3.put("age", "1"); list.add(map1); list.add(map2); list.add(map3); LinkedHashMap
              
               >> 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
               
                
                 > dataList = new ArrayList<>(); Map
                 
                   map1 = new HashMap<>(16); map1.put("id", "1"); map1.put("name", "1"); Map
                  
                    map2 = new HashMap<>(16); map2.put("id", "1"); map2.put("name", "2"); Map
                   
                     map3 = new HashMap<>(16); map3.put("id", "2"); map3.put("name", "3"); dataList.add(map1); dataList.add(map2); dataList.add(map3); Map
                    
                     >> listLinkedHashMap = new LinkedHashMap<>(); Map
                     
                      >> 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
                      
                       >> 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
                       
                         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
                        
                         > ageMap = persons.stream().sorted(Comparator.comparingInt(Person::getAge)).collect(Collectors.groupingBy(Person::getAge, LinkedHashMap::new, Collectors.toList())); System.out.println("ageMap = " + ageMap); }}