Java String、Date、Calendar、LocalDate和LocalDateTime互转

目录

一、String和Date互转

1.1 String时间转为Date

1.2 Date转为String

二、String和Calendar互转

2.1 String时间转为Calendar

2.2 Calendar转为String

三、String和LocalDate（LocalDateTime）互转

3.1 String时间转为LocalDate（LocalDateTime）

3.2 LocalDate（LocalDateTime）转为String

四、Date和Calendar互转

4.1 Date转为Calendar

4.2 Calendar转为Date

五、Date和LocalDate（LocalDateTime）互转

5.1 Date转为LocalDate（LocalDateTime）

5.2 LocalDate（LocalDateTime）转为Date

六、Calendar和LocalDat（LocalDateTime）互转

6.1 Calendar转为LocalDate（LocalDateTime）

6.2 LocalDat（LocalDateTime）转为Calendar

七、LocalDate和LocalDateTime互转

7.1 LocalDate转LocalDateTime

7.2 LocalDateTime转LocalDate

一、String和Date互转

1.1 String时间转为Date

private Date stringToDate(String dateStr, String pattern) {try {return new SimpleDateFormat(pattern).parse(dateStr);} catch (Throwable ignore) {// TODO 时间转换异常日期}return null;}

调方法 stringToDate(Sring, pattern)：

System.out.println(stringToDate("2023-11", "yyyy-MM"));System.out.println(stringToDate("2023-11-11", "yyyy-MM-dd"));System.out.println(stringToDate("2023-11-11 11", "yyyy-MM-dd hh"));System.out.println(stringToDate("2023-11-11 11:11", "yyyy-MM-dd hh:mm"));System.out.println(stringToDate("2023-11-11 11:11:11", "yyyy-MM-dd hh:mm:ss"));

注：第一个参数的格式必须与第二个参数的模式一致才能正常转换

运行结果：

Wed Nov 01 00:00:00 CST 2023Sat Nov 11 00:00:00 CST 2023Sat Nov 11 11:00:00 CST 2023Sat Nov 11 11:11:00 CST 2023Sat Nov 11 11:11:11 CST 2023

1.2 Date转为String

private String dateToString(Date date, String pattern) {return new SimpleDateFormat(pattern).format(date);}

调方法dateToString(Date, pattern)，可根据第二个参数模式来获取对应模式的时间对应字符串格式：

System.out.println(dateToString(new Date(), "yyyy"));System.out.println(dateToString(new Date(), "yyyy-MM"));System.out.println(dateToString(new Date(), "yyyy-MM-dd"));System.out.println(dateToString(new Date(), "yyyy-MM-dd hh"));System.out.println(dateToString(new Date(), "yyyy-MM-dd hh:mm"));System.out.println(dateToString(new Date(), "yyyy-MM-dd hh:mm:ss"));

运行结果：

20232023-082023-08-012023-08-01 112023-08-01 11:402023-08-01 11:40:26

二、String和Calendar互转

2.1 String时间转为Calendar

private Calendar stringToCalendar(String dateStr, String pattern) {try {SimpleDateFormat sdf= new SimpleDateFormat(pattern);Date date = sdf.parse(dateStr);Calendar calendar = Calendar.getInstance();calendar.setTime(date);return calendar;} catch (Throwable ignore) {// TODO 时间字符串转Calendar异常}return null;}

调用方法stringToCalendar(String, pattern)：

Calendar calendar0 = stringToCalendar("2023-08-05", "yyyy");Calendar calendar1 = stringToCalendar("2023-08-05", "yyyy-MM");Calendar calendar2 = stringToCalendar("2023-08-05 11:11:11", "yyyy-MM-dd hh:mm:ss");System.out.println(calendar0.getTime());System.out.println(calendar1.getTime());System.out.println(calendar2.getTime());

注：第一个参数的格式与第二个参数的模式不一定要求强一致，但若String只有年月日，模式不能有时分秒

运行结果：

Sun Jan 01 00:00:00 CST 2023Tue Aug 01 00:00:00 CST 2023Sat Aug 05 11:11:11 CST 2023

说明：根据日期模式格式化时间对象时，若模式只有年月则日为1号，若模式没有年份则月日为01月01日，模式没有时/分/秒 则为0

2.2 Calendar转为String

private String calendarToString(Calendar calendar, final String pattern) {SimpleDateFormat sdf = new SimpleDateFormat(pattern);return sdf.format(calendar.getTime());}

调用方法calendarToString(Calendar, pattern)，第二个参数为输出的格式模式：

System.out.println(calendarToString(Calendar.getInstance(), "yyyy-MM"));System.out.println(calendarToString(Calendar.getInstance(), "yyyy-MM-dd"));System.out.println(calendarToString(Calendar.getInstance(), "yyyy-MM-dd hh"));System.out.println(calendarToString(Calendar.getInstance(), "yyyy-MM-dd hh:mm"));System.out.println(calendarToString(Calendar.getInstance(), "yyyy-MM-dd hh:mm:ss"));

运行结果：

2023-082023-08-012023-08-01 112023-08-01 11:592023-08-01 11:59:13

三、String和LocalDate（LocalDateTime）互转

3.1 String时间转为LocalDate（LocalDateTime）

private LocalDate stringToLocalDate(String dateStr, String pattern) {DateTimeFormatter df = DateTimeFormatter.ofPattern(pattern);return LocalDate.parse(dateStr, df);}private LocalDateTime stringToLocalDateTime(String dateStr, String pattern) {DateTimeFormatter df = DateTimeFormatter.ofPattern(pattern);return LocalDateTime.parse(dateStr, df);}

调方法 stringToLocalDate(Sring, pattern)，第二个参数模式必须有年月日，第一个参数的格式必须与第二个参数的模式一致才能正常转换

System.out.println(stringToLocalDate("2023-08-01", "yyyy-MM-dd"));System.out.println(stringToLocalDate("2023-08-02 11", "yyyy-MM-dd hh"));System.out.println(stringToLocalDate("2023-08-02 11:12", "yyyy-MM-dd hh:mm"));System.out.println(stringToLocalDate("2023-08-02 11:12:13", "yyyy-MM-dd hh:mm:ss"));System.out.println(stringToLocalDateTime("2023-08-02 11:12:13", "yyyy-MM-dd hh:mm:ss"));

运行结果：

2023-08-012023-08-022023-08-022023-08-02java.time.format.DateTimeParseException: Text '2023-08-02 11:12:13' could not be parsed: Unable to obtain LocalDateTime from TemporalAccessor: {MinuteOfHour=12, SecondOfMinute=13, MilliOfSecond=0, MicroOfSecond=0, HourOfAmPm=11, NanoOfSecond=0},ISO resolved to 2023-08-02 of type java.time.format.Parsed

注：报错的原因是stringToLocalDateTime方法第二个参数模式的小时hh 采用12小时，反解析时不知道上午还是下午，改成24小时制“yyyy-MM-ddHH:mm:ss”即可。

3.2 LocalDate（LocalDateTime）转为String

private String localDateToString(LocalDate localDate, String pattern) {return localDate.format(DateTimeFormatter.ofPattern(pattern));}private String localDateToString(LocalDateTime localDateTime, String pattern) {return localDateTime.format(DateTimeFormatter.ofPattern(pattern));}

只需要年月日用LocalDate，若需要时分秒用LocalDateTime

调方法localDateToString：

System.out.println(localDateToString(LocalDate.now(), "yyyy"));System.out.println(localDateToString(LocalDate.now(), "yyyy-MM"));System.out.println(localDateToString(LocalDate.now(), "yyyy-MM-dd"));System.out.println(localDateToString(LocalDateTime.now(), "yyyy-MM-dd HH"));System.out.println(localDateToString(LocalDateTime.now(), "yyyy-MM-dd HH:mm"));System.out.println(localDateToString(LocalDateTime.now(), "yyyy-MM-dd HH:mm:ss"));

运行结果：

20232023-082023-08-012023-08-01 122023-08-01 12:032023-08-01 12:03:44

四、Date和Calendar互转

4.1 Date转为Calendar

private Calendar dateToCalendar(Date date) {Calendar cal = Calendar.getInstance();cal.setTime(date );return cal;}

调方法dateToCalendar(Date)：

Calendar calendar = dateToCalendar(new Date());System.out.println(calendar.getTime());

运行结果：

Tue Aug 01 12:08:41 CST 2023

4.2 Calendar转为Date

private Date calendarToDate(Calendar calendar) {return calendar.getTime();}

调方法calendarToDate(Calendar):

System.out.println(calendarToDate(Calendar.getInstance()));

运行结果：

Tue Aug 01 12:10:21 CST 2023

五、Date和LocalDate（LocalDateTime）互转

5.1 Date转为LocalDate（LocalDateTime）

private LocalDate dateToLocalDate(Date date) {// 将java.util.Date转换为ZonedDateTime。Instant instant = date.toInstant();ZoneId zoneId = ZoneId.systemDefault();ZonedDateTime zonedDateTime = instant.atZone(zoneId);// 使用它的toLocalDate（）方法从ZonedDateTime获取LocalDatereturn zonedDateTime.toLocalDate();}private LocalDateTime dateToLocalDateTime(Date date) {// 将Date对象转换成为Instant对象Instant instant = date.toInstant();// 将瞬时对象转换成为LocalDateTime对象return LocalDateTime.ofInstant(instant, ZoneId.systemDefault());}

调dateToLocalDate(Date)，转LocalDateTime调dateToLocalDateTime(Date)：

System.out.println(dateToLocalDate(new Date()));System.out.println(dateToLocalDateTime(new Date()));

运行结果：

2023-08-012023-08-01T12:22:39.742

5.2 LocalDate（LocalDateTime）转为Date

private Date localDateToDate(LocalDate localDate) {ZoneId zoneId = ZoneId.systemDefault();ZonedDateTime zonedDateTime = localDate.atStartOfDay(zoneId);// 将时区对象转换成为瞬时对象Instant instant2 = zonedDateTime.toInstant();// 通过Date提供的静态方法将瞬时对象转换为Date对象return Date.from(instant2);}private Date localDateTimeToDate(LocalDateTime localDateTime) {// 将LocalDateTime对象转换成为时区对象ZonedDateTime zonedDateTime = localDateTime.atZone(ZoneId.systemDefault());// 将时区对象转换成为瞬时对象Instant instant2 = zonedDateTime.toInstant();// 通过Date提供的静态方法将瞬时对象转换为Date对象return Date.from(instant2);}

LocalDateTime调localDateTimeToDate(LocalDateTime )，LocalDate调localDateToDate(LocalDate )：

System.out.println(localDateToDate(LocalDate.now()));System.out.println(localDateTimeToDate(LocalDateTime.now()));

运行结果：

Tue Aug 01 00:00:00 CST 2023Tue Aug 01 12:25:06 CST 2023

六、Calendar和LocalDat（LocalDateTime）互转

6.1 Calendar转为LocalDate（LocalDateTime）

调4.2由Calendar转为Date，再调5.1转为LocalDate/LocalDateTime：

System.out.println(dateToLocalDate(calendarToDate(Calendar.getInstance())));System.out.println(dateToLocalDateTime(calendarToDate(Calendar.getInstance())));

运行结果：

2023-08-012023-08-01T12:33:01.151

6.2 LocalDat（LocalDateTime）转为Calendar

调5.2由LocalDate转为Date，再调4.1转为Calendar：

Calendar calendar1 = dateToCalendar(localDateToDate(LocalDate.now()));Calendar calendar2 = dateToCalendar(localDateTimeToDate(LocalDateTime.now()));System.out.println(calendar1.getTime());System.out.println(calendar2.getTime());

运行结果：

Tue Aug 01 00:00:00 CST 2023Tue Aug 01 12:35:47 CST 2023

七、LocalDate和LocalDateTime互转

7.1 LocalDate转LocalDateTime

private LocalDateTime localDateToLocalDateTime(LocalDate localDate) {return dateToLocalDateTime(localDateToDate(localDate));}

7.2 LocalDateTime转LocalDate

private LocalDate localDateTimeToLocalDate(LocalDateTime localDateTime) {return localDateTime.toLocalDate();}

调7.1和7.2:

System.out.println(localDateToLocalDateTime(LocalDate.now()));System.out.println(localDateTimeToLocalDate(LocalDateTime.now()));

运行结果：

2023-08-01T00:002023-08-01

注：String为java.lang.String，Date为java.util.Date，Calendar为java.util.Calendar，LocalDate为java.time.LocalDate，LocalDateTime为java.time.LocalDateTime。