工作中常用到的 java8 相关操作总结

        Person person = new Person();        person.setName("4");        person.setAge(16);        person.setWeight(15L);        person.setGroup("group1");
        //升序        list.sort(Comparator.comparing(Person::getAge));        //降序        list.sort(Comparator.comparing(Person::getAge).reversed());        //年龄一样，则按照姓名排序        list.sort(Comparator.comparing(Person::getAge).thenComparing(Person::getName));
        //年龄小于10，然后按重量排序        list.stream().filter(item -> item.getAge() < 10)                .sorted(Comparator.comparing(Person::getWeight))                .collect(Collectors.toList());        //distinct去重        list.stream().filter(item -> item.getAge() > 10)                .distinct()                .collect(Collectors.toList());        //skip筛选跳跃        list.stream().filter(item -> item.getAge() > 10)                .skip(2)                .collect(Collectors.toList());        //map映射        List<String> names = list.stream().filter(item -> item.getAge() > 10)                .map(Person::getName)                .collect(Collectors.toList());
        //anyMatch匹配        list.stream().anyMatch(item -> item.getAge() > 10);        //allMatch全部匹配        list.stream().allMatch(item -> item.getAge() > 10);        //noneMatch匹配，有一个匹配就返回false        list.stream().noneMatch(item -> item.getAge() > 10);
        //findAny任意元素        Person person5 = list.stream().filter(item -> item.getAge() > 10)                .findAny().orElse(null);        //findFirst第一个元素        Person person6 = list.stream().filter(item -> item.getAge() > 10)                .findFirst().orElse(null);
        //元素求和        Integer totalAge = list.stream().map(Person::getAge).reduce(0, (a, b) -> a + b);        Integer totalAge1 = list.stream().map(Person::getAge).reduce(0, Integer::sum);        Integer total = list.stream().collect(Collectors.summingInt(Person::getAge));        Integer tt = list.stream().mapToInt(Person::getAge).sum();        System.out.println(tt);
        //最大、最小值        Integer max = list.stream().map(Person::getAge).reduce(0, Integer::max);        Integer max1 = list.stream().map(Person::getAge).reduce(Integer::max).get();
        //连接字符串        String name = list.stream().map(Person::getName).collect(Collectors.joining(","));        System.out.println(name);
        //分组        Map<String, List<Person>> map = list.stream().collect(Collectors.groupingBy(Person::getName));        Map<String, Integer> nameMap = list.stream().collect(Collectors.toMap(Person::getName, Person::getAge));        Map<String, Person> personMap1 = list.stream().collect(Collectors.toMap(Person::getName, Function.identity()));        Map<String, Person> personMap2 = list.stream().collect(Collectors.toMap(e -> e.getName() + "wyt", Function.identity()));        //分组排重，取第二个元素        Map<String, Person> personMap3 = list.stream().collect(Collectors.toMap(Person::getName, e -> e, (e1, e2) -> e2));        System.out.println(personMap3);        //先按名字分组，然后找年龄最大的分组        Map<String, Person> personMap = list.stream().collect(Collectors.groupingBy(Person::getGroup,                Collectors.collectingAndThen(Collectors.maxBy(Comparator.comparing(Person::getAge)),                        Optional::get)));        System.out.println(personMap);

        //optional使用        String name1 = Optional.ofNullable(person1).map(Person::getName).orElse("");        System.out.println(name1);
        //localDate        LocalDate localDate = LocalDate.of(2023,11, 1);        System.out.println(localDate);
        LocalTime localTime = LocalTime.of(12,2,3);        System.out.println(localTime);
        LocalDateTime localDateTime = LocalDateTime.of(2023,11,2, 12,3,24);        System.out.println(localDateTime);
        //两个时间间隔        Long days = LocalDateTimeUtil.between(LocalDateTime.now(),                LocalDateTime.now().plusDays(1)).toDays();        System.out.println(days);        //时间比较        if(LocalDateTime.now().isBefore(LocalDateTime.now().plusDays(1))) {            System.out.println(true);        }        //开始时间和结束时间        System.out.println(LocalDateTime.of(LocalDate.now(), LocalTime.MIN));        System.out.println(LocalDateTime.of(LocalDate.now(), LocalTime.MAX));