List stream 对象 属性去重

单值去重不写了,记录对象去重

随手一个对象:

1@Data
2@AllArgsConstructor
3public class Milk {
4    private Integer key;
5    private String value;
6}

操作:

1package com.yus.util;
2
3import java.util.*;
4import java.util.stream.Collectors;
5
6import static java.util.Comparator.comparing;
7import static java.util.Comparator.comparingLong;
8import static java.util.stream.Collectors.collectingAndThen;
9import static java.util.stream.Collectors.toCollection;
10
11public class main {
12    public static void main(String[] args) {
13        Milk milk0=new Milk(0,"a");
14        Milk milk1=new Milk(1,"b");
15        Milk milk2=new Milk(0,"c");
16        List<Milk> list=new ArrayList<>();
17        list.add(milk0);
18        list.add(milk1);
19        list.add(milk2);
20        //去重
21        List<Milk> uniqueMilk = list.stream().collect(
22                collectingAndThen(
23                        toCollection(() -> new TreeSet<>(comparing(n->n.getKey()))),ArrayList::new)
24        );
25
26        for (Milk m:uniqueMilk) {
27            System.out.println(m.toString());
28        }
29
30    }
31}

操作底层是set,视图,collection...一堆东西,还是有点意思的,不记录了,有兴趣可深入

任何Object类型去重...~

1import java.util.ArrayList;
2import java.util.HashMap;
3import java.util.List;
4import java.util.Map;
5import java.util.concurrent.ConcurrentHashMap;
6import java.util.function.Function;
7import java.util.function.Predicate;
8import java.util.stream.Collectors;
9
10public class TestMain {
11
12    public static void main(String[] args) {
13
14        List<Map<String, Object>> list = new ArrayList<>();
15
16        Map<String, Object> map = new HashMap<>();
17        map.put("id", "11");
18        map.put("orderno", "No.1");
19        list.add(map);
20
21        Map<String, Object> map1 = new HashMap<>();
22        map1.put("id", "2222");
23        map1.put("orderno", "No.2");
24        list.add(map1);
25
26        Map<String, Object> map2 = new HashMap<>();
27        map2.put("id", "33");
28        map2.put("orderno", "No.2");
29        list.add(map2);
30
31        Map<String, Object> map3 = new HashMap<>();
32        map3.put("id", "444");
33        map3.put("orderno", "No.1");
34        list.add(map3);
35
36        List<Map<String, Object>> collect = list.stream().filter(distinctByKey(n -> n.get("orderno")))
37                .collect(Collectors.toList());
38
39        collect.forEach(System.out::println);
40    }
41
42    private static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) {
43        ConcurrentHashMap<Object, Boolean> map = new ConcurrentHashMap<>();
44        return t -> map.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;
45    }
46}