Java8日期类LocalDate & LocalDateTim

一、JDK7 的日期 和 JDK8 的日期对比

JDK7 创建一个时间

Date date0 = new Date();

JDK8 创建一个时间

LocalDate today = LocalDate.now();

我们先看看这执行出来都是啥？
Date输出：

Wed Apr 13 13:19:06 CST 2022

LocalDate输出：

2022-04-13

首先我们从输出上，直接就感觉有点难受，Date输出的看起来就不是那么的直观，所以，当你想要直观的去输出这个时间的时候，可能就得用到 SimpleDateFormat 去格式化一下我们的这个时间。但是如果是用 LocalDate 就不会有这种顾虑了。
Date格式化：

SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 HH时mm分ss秒");
String str = sdf.format(date0);

JDK1.8之后我们可以使用 java.time.format.DateTimeFormatter来进行日期时间的格式化。

 LocalDate now = LocalDate.now();
 DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy/MM/dd");

 String JDK8Time = now.format(dateTimeFormatter);
 System.out.println("JDK8格式化后的时间数据=="+JDK8Time);

二、SimpleDateFormat & DateTimeFormatter

SimpleDateFormat是个线程不安全的，使用的时候，只能在方法内部创建新的局部变量。而DateTimeFormatter不但是不变对象，它还是线程安全的。所以DateTimeFormatter可以只创建一个实例，到处引用。

三、JDK8日期的各种用法

3.1 LocalDate转String

LocalDate localDate = LocalDate.now();

DateTimeFormatter fmt = DateTimeFormatter.ofPattern("yyyy-MM-dd");

String dateStr = localDate.format(fmt);

System.out.println("LocalDate转String：" + dateStr);

转换结果

LocalDate转String：2022/04/14

3.2 Date转LocalDateTime

Date date = new Date();
LocalDateTime localDateTime = (date).toInstant().atZone(ZoneId.systemDefault()).toLocalDateTime();
System.out.println("localDateTime=" + localDateTime);

转换结果

localDateTime=2022-10-25T09:50:06.506

3.3 时间戳转LocalDateTime

long timestamp = System.currentTimeMillis();

Instant instant1 = Instant.ofEpochMilli(timestamp);

System.out.println("时间戳 转 LocalDateTime：" + LocalDateTime.ofInstant(instant1, ZoneId.systemDefault()));

转换结果

时间戳 转 LocalDateTime：2022-04-14T10:09:14.780

3.4 LocalDateTime转时间戳

long now = LocalDateTime.now().toEpochSecond(ZoneOffset.of("+8"));

long end = LocalDateTime.of(LocalDate.from(LocalDateTime.now().with(TemporalAdjusters.lastDayOfMonth())), LocalTime.MAX).toEpochSecond(ZoneOffset.of("+8"));

3.5 String 转 LocalDateTime

//String 转 LocalDateTime
LocalDateTime date = LocalDateTime.parse("2022-06-01"+" 00:00:00", DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));

3.6 LocalDateTime本月开始/结束时间

//LocalDateTime 本月开始时间 2022-06-01T00:00
LocalDateTime startDateTime = LocalDateTime.now().with(TemporalAdjusters.firstDayOfMonth()).with(LocalTime.MIN);

//LocalDateTime 本月结束时间 2022-06-30T23:59:59.999999999
LocalDateTime endDateTime = LocalDateTime.now().with(TemporalAdjusters.lastDayOfMonth()).with(LocalTime.MAX);

3.7 LocalDate今天/昨天/明天/下周

  //今天：2022-06-07
  System.out.println(LocalDate.now());

  //昨天：2022-06-06
  System.out.println(LocalDate.now().plusDays(-1));

  //明天：2022-06-08
  System.out.println(LocalDate.now().plusDays(1));

  //下周：2022-06-14
  System.out.println(LocalDate.now().plusWeeks(1));

3.8 LocalDateTime 转 LocalDate

LocalDateTime time = LocalDateTime.now();
LocalDate day = time.toLocalDate();

3.9 LocalDate本月开始/结束时间

LocalDate day = LocalDate.now();

//本月开始日期
LocalDate startDay = day.with(TemporalAdjusters.firstDayOfMonth());

//本月结束日期
LocalDate endDay = day.with(TemporalAdjusters.lastDayOfMonth());

四、转换

//1.LocalDate转Date

LocalDate nowLocalDate = LocalDate.now();
Date date = Date.from(localDate.atStartOfDay(ZoneOffset.ofHours(8)).toInstant());

//2.LocalDateTime转Date

LocalDateTime localDateTime = LocalDateTime.now();
Date date = Date.from(localDateTime.atZone(ZoneOffset.ofHours(8)).toInstant());

//3.Date转LocalDateTime(LocalDate)

Date date =newDate();
LocalDateTime localDateTime = date.toInstant().atZone(ZoneOffset.ofHours(8)).toLocalDateTime();
LocalDate localDate = date.toInstant().atZone(ZoneOffset.ofHours(8)).toLocalDate();

//4.LocalDate转时间戳

LocalDate localDate = LocalDate.now();
longtimestamp = localDate.atStartOfDay(ZoneOffset.ofHours(8)).toInstant().toEpochMilli();

//5.LocalDateTime转时间戳

LocalDateTime localDateTime = LocalDateTime.now();
longtimestamp = localDateTime.toInstant(ZoneOffset.ofHours(8)).toEpochMilli();

//6.时间戳转LocalDateTime(LocalDate)

longtimestamp = System.currentTimeMillis();
LocalDate localDate = Instant.ofEpochMilli(timestamp).atZone(ZoneOffset.ofHours(8)).toLocalDate();
LocalDateTime localDateTime = Instant.ofEpochMilli(timestamp).atZone(ZoneOffset.ofHours(8)).toLocalDateTime();

//7.LocalDateTime 转 LocalDate 
LocalDateTime time = LocalDateTime.now();
LocalDate day = time.toLocalDate();

五、获取两个日期中间的所有天数，所有月份

5.1 LocalDate

import java.time.LocalDate;
import java.time.temporal.ChronoUnit;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Stream;

public class Client {

    public static void main(String[] args) {
        LocalDate startDay = LocalDate.parse("2022-07-01");
        LocalDate endDay = LocalDate.parse("2022-08-01");

        List<String> day = getBetweenDate(startDay.toString(), endDay.toString(),1);
        //System.out.println("day = " + day);

        List<String> month = getBetweenDate("2022-07", "2022-11",2);
        System.out.println("month = " + month);
    }

    /**
     * 获取两个日期中间的所有天数，所有月份
     * @param start
     * @param end
     * @param type
     * @return
     */
    public static List<String> getBetweenDate(String start, String end, Integer type) {
        List<String> list = new ArrayList<>();
        if(start.length()<8){
            start+="-01";
            end+="-01";
        }
        LocalDate startDate = LocalDate.parse(start);
        LocalDate endDate = LocalDate.parse(end);
        long distance = 0L;
        if (type == 1) {
            distance = ChronoUnit.DAYS.between(startDate, endDate);
            Stream.iterate(startDate, d -> d.plusDays(1)).limit(distance + 1).forEach(f -> list.add(f.toString()));
        } else if(type==2) {
            distance = ChronoUnit.MONTHS.between(startDate, endDate);
            Stream.iterate(startDate, d -> d.plusMonths(1)).limit(distance + 1).forEach(f -> list.add(f.toString().substring(0,7)));
        }
        return list;
    }
}

5.2 LocalDateTime

public class LocalDateTimeUtil {

    public LocalDateTimeUtil() {
        throw new RuntimeException("工具类，不用创建");
    }

    /**
     * 获取两个日期中间的所有天数
     *
     * @return
     */
    public static List<LocalDateTime> listBetweenDate(String startDayStr, String endDayStr) {
        String[] startArray = startDayStr.split(" ");
        String[] endArray = endDayStr.split(" ");

        String start = startArray[0];
        String startTime = startArray[1];

        String end = endArray[0];
        String endTime = endArray[1];

        if (startTime.equals(endTime)) {
            //如果时间相同，则不用拆开处理了，
            LocalDateTime startDay = LocalDateTime.parse(startDayStr, DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
            LocalDateTime endDay = LocalDateTime.parse(endDayStr, DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
            return listBetweenDate(startDay, endDay);
        } else {
            //"2022-11-04 19:30:00", "2022-11-05 16:30:00"  需要拆开比较，不然只会返回一天，出现BUG
            LocalDateTime startDay = LocalDateTime.parse(start + " 00:00:00", DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
            LocalDateTime endDay = LocalDateTime.parse(end + " 00:00:00", DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));

            List<LocalDateTime> dayTimeList = listBetweenDate(startDay, endDay);
            List<LocalDateTime> newDayTimeList = new ArrayList<>();
            for (LocalDateTime item : dayTimeList) {
                LocalDateTime newDayTime = LocalDateTime.of(item.toLocalDate(), LocalTime.parse(startTime));
                newDayTimeList.add(newDayTime);
            }
            newDayTimeList.remove(dayTimeList.size() - 1);

            LocalDateTime lastDayTime = dayTimeList.get(dayTimeList.size() - 1);
            LocalDateTime lastNewDayTime = LocalDateTime.of(lastDayTime.toLocalDate(), LocalTime.parse(endTime));
            newDayTimeList.add(lastNewDayTime);

            return newDayTimeList;
        }
    }

    /**
     * 获取两个日期中间的所有天数
     *
     * @return
     */
    public static List<LocalDateTime> listBetweenDate(LocalDateTime startDay, LocalDateTime endDay) {
        List<LocalDateTime> list = new ArrayList<>();
        long distance = ChronoUnit.DAYS.between(startDay, endDay);
        Stream.iterate(startDay, d -> d.plusDays(1)).limit(distance + 1).forEach(f -> list.add(f));
        return list;
    }
}

测试

public class Test {

    public static void main(String[] args) {
        List<LocalDateTime> timeList = LocalDateTimeUtil.listBetweenDate("2022-11-04 19:30:00", "2022-11-05 16:30:00");
        
        //[2022-11-04T19:30, 2022-11-05T16:30]
        System.out.println(timeList);
    }
}

六、设置日期的最后时间

public static void main(String[] args) {
        //2022-10-13
        LocalDate today = LocalDate.now();
        System.out.println(today);

        //2022-10-13 23:59:59
        LocalDateTime todayLastTime = today.atTime(23,59,59);
        System.out.println(todayLastTime);
 }

七、LocalDateTime两个时间相差的天数,小时数,分钟数,毫秒数

    public static void main(String[] args) {
        LocalDateTime start = LocalDateTime.of(2022, 5, 7, 1, 1);
        LocalDateTime end = LocalDateTime.of(2022, 5, 8, 1, 1);
        System.out.println("相差的天数: " + Duration.between(start, end).toDays() + "天");
        System.out.println("相差的小时数: " + Duration.between(start, end).toHours() + "小时");
        System.out.println("相差的分钟数: " + Duration.between(start, end).toMinutes() + "分钟");
        System.out.println("相差的毫秒数: " + Duration.between(start, end).toMillis() + "毫秒");
    }

运行结果

相差的天数: 1天
相差的小时数: 24小时
相差的分钟数: 1440分钟
相差的毫秒数: 86400000毫秒

八、LocalDateTime时间加减法

LocalDateTime time = LocalDateTime.now();

time = time.plusMinutes(5);//获取当前时间并加5分钟
time = time.minusMinutes(5);//获取当前时间并减去5分钟
time = time.plusHours(5);//获取当前时间并加5小时
time = time.minusHours(5);//获取当前时间并减去5小时

九、当天开始/结束时间

public static void main(String[] args) {
        LocalDateTime date = LocalDateTime.parse("2022-11-09" + " 12:32:01", DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));

        LocalDateTime dateStart = LocalDateTime.of(date.toLocalDate(), LocalTime.MIN);
        LocalDateTime dateEnd = LocalDateTime.of(date.toLocalDate(), LocalTime.MAX);

        System.out.println(dateStart);
        System.out.println(dateEnd);
        
        String dayStr = date.toLocalDate().format(DateTimeFormatter.ofPattern("yyyy-MM-dd"));
        LocalDateTime dataEnd2 = LocalDateTime.parse(dayStr + " " + "23:59:59", DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
        System.out.println(dataEnd2);
    }