1 import com.google.common.collect.Lists;
2
3 import java.math.BigDecimal;
4 import java.util.*;
5 import java.util.function.Function;
6 import java.util.function.Predicate;
7 import java.util.stream.Collectors;
8 import java.util.concurrent.ConcurrentHashMap;
9
10 import static java.util.stream.Collectors.collectingAndThen;
11 import static java.util.stream.Collectors.toCollection;
12 import static java.util.Comparator.comparingLong;;
13
14 public class test {
15
16 public void test(){
17 List<UserDomain> list = Lists.newArrayList();
18 //判断对象属性去重
19 long count = list.stream().filter(distinctByKey(UserDomain :: getUserName)).distinct().count();
20 if(count < list.size()){
21
22 }
23
24 //根据对象属性去重
25 list = list.stream().collect(
26 collectingAndThen(toCollection(() -> new TreeSet<>(comparingLong(UserDomain::getId))), ArrayList::new)
27 );
28 //去重
29 list = list.stream().distinct().collect(Collectors.toList());
30
31 //排序
32 list.sort(Comparator.comparing(UserDomain::getUserName));
33 list.sort(Comparator.comparing(UserDomain::getUserName).reversed());
34 list = list.stream().sorted(Comparator.comparing(UserDomain::getUserName, Comparator.nullsFirst(Comparator.naturalOrder()))).collect(Collectors.toList());
35 list = list.stream().sorted(Comparator.comparing(UserDomain::getUserName, Comparator.nullsFirst(Comparator.naturalOrder())).reversed()).collect(Collectors.toList());
36
37 //过滤
38 list = list.stream().filter(a -> a.getUserName().equals("张三")).collect(Collectors.toList());
39
40 //求和
41 BigDecimal totalMoney = list.stream().map(UserDomain::getUnitPrice).reduce(BigDecimal.ZERO, BigDecimal::add);
42
43 //遍历(使用return可以达到continue的效果)
44 list.forEach(userList -> {
45 return;
46 });
47 //groupBy分组
48 Map<Long, List<UserDomain>> groupBy = list.stream().collect(Collectors.groupingBy(UserDomain::getId));
49
50 //id为key，对象为value转Map
51 Map<Long,UserDomain> userMap = list.stream().collect(Collectors.toMap(UserDomain::getId, a -> a,(k1,k2)->k1));
52 //去重
53 userMap = list.stream().collect(Collectors.toMap(UserDomain::getId, user -> user,(k1,k2)->k1));
54 //JSONArray.toJSONString(userMap);
55
56 //获取对象list中某个属性的值的lis
57 List<String> nameList = list.stream().map(UserDomain::getUserName).collect(Collectors.toList());
58 List<String> nameList1 = list.stream().map(e -> e.getUserName()).collect(Collectors.toList());
59
60
61 }
62
63
64 private static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) {
65 Map<Object, Boolean> seen = new ConcurrentHashMap<>();
66 return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;
67 }
68
69 }
