使用Java8的Stream进行多字段排序以及剔除非空字段排序

　　使用 Stream的sort() 方法，并结合 Comparator 类 进行排序，主要解决以下两个问题：

　　1）当某个字段为空时，怎么进行排序？---使用 Comparator.nullsFirst() 或者 Comparator.nullsLast( ) 进行非空的剔除

　　2）如果比较两个字段？---使用 thenComparing( )

 1 package com.demrystv.stonestrong.stone.streamTest;
 2 
 3 import com.alibaba.fastjson.JSON;
 4 import org.junit.Test;
 5 
 6 import java.util.Arrays;
 7 import java.util.Comparator;
 8 import java.util.List;
 9 import java.util.stream.Collectors;
10 
11 public class StreamController {
12 
13     @Test
14     public void streamSortTest(){
15         User user1 = new User();
16         user1.setAge(36);
17         user1.setUserName("Bryant");
18         user1.setAddress("LA");
19         user1.setPhone("11111");
20 
21         User user2 = new User();
22         user2.setAge(37);
23         user2.setUserName("James");
24         user2.setPhone("22222");
25 
26         User user3 = new User();
27         user3.setAge(39);
28         user3.setUserName("Harden");
29         user3.setAddress("Houston");
30         user3.setPhone("33333");
31 
32         User user4 = new User();
33         user4.setAge(28);
34         user4.setUserName("Durant");
35         user4.setAddress("NY");
36 
37         User user5 = new User();
38         user5.setAge(29);
39         user5.setUserName("Wade");
40         user5.setAddress("Miami");
41         user5.setPhone("55555");
42 
43 
44 
45         List<User> userList = Arrays.asList(user1, user2, user3, user4, user5);
46         List<User> collect1 = userList.stream().sorted(Comparator.comparing(User::getAddress, Comparator.nullsFirst(String::compareTo))).collect(Collectors.toList());
47         System.out.println("根据地址正序排序,null的在前面: ");
48         System.out.println(JSON.toJSONString(collect1));
49         System.out.println("=========================");
50         System.out.println();
51 
52         List<User> collect2 = userList.stream().sorted(Comparator.comparing(User::getAddress, Comparator.nullsLast(String::compareTo))).collect(Collectors.toList());
53         System.out.println("根据地址正序排序,null的在后面: ");
54         System.out.println(JSON.toJSONString(collect2));
55         System.out.println("=========================");
56         System.out.println();
57 
58         List<User> collect3 = userList.stream().sorted(Comparator.comparing(User::getAddress, Comparator.nullsFirst(String::compareTo)).reversed()).collect(Collectors.toList());
59         System.out.println("根据地址逆序排序,null的在后面: ");
60         System.out.println(JSON.toJSONString(collect3));
61         System.out.println("=========================");
62         System.out.println();
63 
64         List<User> collect4 = userList.stream().sorted(Comparator.comparing(User::getAddress, Comparator.nullsFirst(String::compareTo)).
65                 thenComparing(User::getPhone, Comparator.nullsFirst(String::compareTo)).reversed()).collect(Collectors.toList());
66         System.out.println("先根据地址正序排序,再根据电话逆序排序,null的在后面: ");
67         System.out.println(JSON.toJSONString(collect4));
68         System.out.println("=========================");
69         System.out.println();
70 
71     }
72 }

　　运行结果如下：

根据地址正序排序,null的在前面: 
[{"age":37,"phone":"22222","userName":"James"},{"address":"Houston","age":39,"phone":"33333","userName":"Harden"},{"address":"LA","age":36,"phone":"11111","userName":"Bryant"},{"address":"Miami","age":29,"phone":"55555","userName":"Wade"},{"address":"NY","age":28,"userName":"Durant"}]
=========================

根据地址正序排序,null的在后面: 
[{"address":"Houston","age":39,"phone":"33333","userName":"Harden"},{"address":"LA","age":36,"phone":"11111","userName":"Bryant"},{"address":"Miami","age":29,"phone":"55555","userName":"Wade"},{"address":"NY","age":28,"userName":"Durant"},{"age":37,"phone":"22222","userName":"James"}]
=========================

根据地址逆序排序,null的在后面: 
[{"address":"NY","age":28,"userName":"Durant"},{"address":"Miami","age":29,"phone":"55555","userName":"Wade"},{"address":"LA","age":36,"phone":"11111","userName":"Bryant"},{"address":"Houston","age":39,"phone":"33333","userName":"Harden"},{"age":37,"phone":"22222","userName":"James"}]
=========================

先根据地址正序排序,再根据电话逆序排序,null的在后面: 
[{"address":"NY","age":28,"userName":"Durant"},{"address":"Miami","age":29,"phone":"55555","userName":"Wade"},{"address":"LA","age":36,"phone":"11111","userName":"Bryant"},{"address":"Houston","age":39,"phone":"33333","userName":"Harden"},{"age":37,"phone":"22222","userName":"James"}]
=========================