一、标题
java stream的常用例子
二、描述
stream在当前互联网技术社区传播的已经很广泛了，且有阿里11.11用stream很好的完成数据处理案例，为此迎着互联网技术风口细细地学习一下stream，说不定能让代码飘起来
三、常用的例子
以下内容均使用该代码作为前提：
1 public class AppTest {
2
3 public static void main(String[] args){
4 List<StreamDemo> list = new ArrayList<>();
5 list.add(StreamDemo.builder().dateValue(LocalDate.now()).intValue(10).strValue("str1").descValue("str1").timeValue(LocalTime.now()).dateTimeValue(LocalDateTime.now()).bigDecimal(BigDecimal.TEN).build());
6 list.add(StreamDemo.builder().dateValue(LocalDate.now()).intValue(15).strValue("str3").descValue("str2").timeValue(LocalTime.now()).dateTimeValue(LocalDateTime.now()).bigDecimal(BigDecimal.ONE).build());
7 list.add(StreamDemo.builder().dateValue(LocalDate.now()).intValue(11).strValue("str6").descValue("str3").timeValue(LocalTime.now()).dateTimeValue(LocalDateTime.now()).bigDecimal(BigDecimal.ZERO).build());
8 list.add(StreamDemo.builder().dateValue(LocalDate.now()).intValue(16).strValue("str8").descValue("str4").timeValue(LocalTime.now()).dateTimeValue(LocalDateTime.now()).bigDecimal(BigDecimal.TEN).build());
9 }
10 }
11 @Builder
12 @AllArgsConstructor
13 @Data
14 class StreamDemo{
15 private String strValue;
16 private String descValue;
17 private Integer intValue=2;
18 private LocalDate dateValue;
19 private LocalTime timeValue;
20 private LocalDateTime dateTimeValue;
21 private BigDecimal bigDecimal;
22
23 public String toString() {
24 return "StreamDemo{" +
25 "strValue=‘" + strValue + ‘\‘‘ +
26 ", descValue=‘" + descValue + ‘\‘‘ +
27 ", intValue=" + intValue +
28 ", dateValue=" + dateValue +
29 ", timeValue=" + timeValue +
30 ", dateTimeValue=" + dateTimeValue +
31 ", bigDecimal=" + bigDecimal +
32 ‘}‘;
33 }
34 }
1、操作数值
1.1、获取累积指
System.out.println(Stream.of(list.get(0),list.get(1),list.get(2)).map(StreamDemo::getIntValue).reduce(10,(n,m)->n*m)); System.out.println(Stream.of(list.get(0),list.get(1),list.get(2)).map(StreamDemo::getIntValue).collect(Collectors.reducing((n,m)->n+m)).get());
1.2、获取最大值
System.out.println(Stream.of(list.get(0),list.get(1),list.get(2)).map(StreamDemo::getIntValue).max((n,m)->n.compareTo(m)).get());
System.out.println(Stream.of(list.get(0),list.get(1),list.get(2)).collect(Collectors.maxBy((n,m)->n.getIntValue().compareTo(m.getIntValue()))).get());
1.3、获取最小值
System.out.println(Stream.of(list.get(0),list.get(1),list.get(2)).map(StreamDemo::getIntValue).min((n,m)->n.compareTo(m)).get());
System.out.println(Stream.of(list.get(0),list.get(1),list.get(2)).collect(Collectors.minBy((n,m)->n.getIntValue().compareTo(m.getIntValue()))).get());
1.4、获取数值集合
Stream.of(list.get(0),list.get(1),list.get(2)).mapToInt(StreamDemo::getIntValue).forEach(System.out::println);
Stream.of(list.get(0),list.get(1),list.get(2)).collect(Collectors.mapping(StreamDemo::getIntValue,Collectors.toList())).forEach(System.out::println);
1.5、将多个数值集合合并为一个数值集合
Stream.of(list.get(0),list.get(1),list.get(2)).flatMapToInt(f-> IntStream.concat(IntStream.of(f.getIntValue()),IntStream.of(f.getBigDecimal().intValue()))).sorted().forEachOrdered(System.out::println);
1.6、获取平均值
System.out.println(Stream.of(list.get(0),list.get(1),list.get(2)).collect(Collectors.averagingInt(StreamDemo::getIntValue)).intValue());
1.7、获取数据统计
System.out.println(Stream.of(list.get(0),list.get(1),list.get(2)).collect(Collectors.summarizingInt(StreamDemo::getIntValue)).toString());
2、操作集合
2.1:、获取集合长度
System.out.println(Stream.of(list.get(0),list.get(1),list.get(2)).count());
System.out.println(Stream.of(list.get(0),list.get(1),list.get(2)).collect(Collectors.counting()));
2.2、限制集合长度
Stream.of(list.get(0),list.get(1),list.get(2)).limit(1).forEach(System.out::println);
2.3、跳过集合前几项
Stream.of(list.get(0),list.get(1),list.get(2)).skip(1).forEach(System.out::println);
2.4、集合排序
Stream.of(list.get(0),list.get(1),list.get(2)).sorted((n,m)->n.getIntValue().compareTo(m.getIntValue())).forEach(System.out::println);
2.5、去重
Stream.of(list.get(0),list.get(1),list.get(2)).distinct().forEach(System.out::println);
2.6、集合过滤
Stream.of(list.get(0),list.get(1),list.get(2)).filter(streamDemo -> StringUtils.isEmpty(streamDemo.getStrValue())).forEach(System.out::println);
System.out.println(Stream.of(list.get(0),list.get(1),list.get(2)).noneMatch(streamDemo -> StringUtils.isEmpty(streamDemo.getStrValue())));
System.out.println(Stream.of(list.get(0),list.get(1),list.get(2)).anyMatch(streamDemo -> StringUtils.isEmpty(streamDemo.getStrValue())));
System.out.println(Stream.of(list.get(0),list.get(1),list.get(2)).allMatch(streamDemo -> StringUtils.isEmpty(streamDemo.getStrValue())));
Stream.of(list.get(0),list.get(1),list.get(2)).collect(Collectors.partitioningBy(streamDemo -> StringUtils.isEmpty(streamDemo.getStrValue()))).forEach((k,v)->System.out.printf("k:%s,v:%s\n",k,v));
2.7、给集合每项添加内容
Stream.of(list.get(0),list.get(1),list.get(2)).peek(streamDemo -> streamDemo.setDescValue(streamDemo.getStrValue())).forEach(System.out::println);
2.8、集合分组
Stream.of(list.get(0),list.get(1),list.get(2)).collect(Collectors.groupingBy(StreamDemo::getStrValue,Collectors.toList())).forEach((k,v)->System.out.printf("k:%s,v:%s\n",k,v));
Stream.of(list.get(0),list.get(1),list.get(2)).collect(Collectors.groupingBy(StreamDemo::getStrValue,Collectors.groupingBy(StreamDemo::getStrValue))).forEach((k,v)->System.out.printf("k:%s,v:%s\n",k,v));
System.out.println(Stream.of(list.get(0),list.get(1),list.get(2)).map(StreamDemo::getStrValue).collect(Collectors.joining(";")));
Stream.of(list.get(0),list.get(1),list.get(2)).collect(Collectors.toMap(StreamDemo::getStrValue,StreamDemo::getDescValue)).forEach((k,v)->System.out.printf("k:%s,v:%s\n",k,v));
System.out.println(Stream.of(list.get(0),list.get(1),list.get(2)).collect(Collectors.mapping(StreamDemo::getStrValue,Collectors.joining(";"))));
2.9、合并集合
Stream.of(list.get(0),list.get(1),list.get(2)).flatMap(f->Stream.concat(Stream.of(f.getIntValue()),Stream.of(f.getBigDecimal()))).forEach(System.out::println);
2.10、将集合转为数组
System.out.println(Arrays.toString(Stream.of(list.get(0),list.get(1),list.get(2)).toArray(t->new StreamDemo[t])));
原文地址：https://www.cnblogs.com/lswater/p/12003473.html
时间： 2024-10-14 11:24:16