How to parse format dates with LocalDateTime Java 8

Question

Java 8 added a new java time API for working with dates and times  JSR 310    I have date and time as string  e g   2014-04-08 12 30    How can I obtain a LocalDateTime instance from the given string   After I finished working with the LocalDateTime object  How can I then convert the LocalDateTime instance back to a string with the same format as shown above

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GET CURRENT UTC TIME IN REQUIRED FORMAT     Current UTC time         OffsetDateTime utc   OffsetDateTime now ZoneOffset UTC               GET LocalDateTime          LocalDateTime localDateTime   utc toLocalDateTime            System out println                   localDateTime               formated UTC time         DateTimeFormatter dTF   DateTimeFormatter ofPattern  yyyy-MM-dd HH mm            System out println   formats as     dTF format localDateTime               GET UTC time for current date         Date now  new Date            LocalDateTime utcDateTimeForCurrentDateTime   Instant ofEpochMilli now getTime    atZone ZoneId of  UTC    toLocalDateTime            DateTimeFormatter dTF2   DateTimeFormatter ofPattern  yyyy-MM-dd HH mm            System out println   formats as     dTF2 format utcDateTimeForCurrentDateTime

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Parsing date and time  To create a LocalDateTime object from a string you can use the static LocalDateTime parse   method  It takes a string and a DateTimeFormatter as parameter  The DateTimeFormatter is used to specify the date time pattern   String str    1986-04-08 12 30   DateTimeFormatter formatter   DateTimeFormatter ofPattern  yyyy-MM-dd HH mm    LocalDateTime dateTime   LocalDateTime parse str  formatter     Formatting date and time  To create a formatted string out a LocalDateTime object you can use the format   method   DateTimeFormatter formatter   DateTimeFormatter ofPattern  yyyy-MM-dd HH mm    LocalDateTime dateTime   LocalDateTime of 1986  Month APRIL  8  12  30   String formattedDateTime   dateTime format formatter       1986-04-08 12 30    Note that there are some commonly used date time formats predefined as constants in DateTimeFormatter  For example  Using DateTimeFormatter ISO DATE TIME to format the LocalDateTime instance from above would result in the string  1986-04-08T12 30 00    The parse   and format   methods are available for all date time related objects  e g  LocalDate or ZonedDateTime

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Both answers above explain very well the question regarding string patterns  However  just in case you are working with ISO 8601 there is no need to apply DateTimeFormatter since LocalDateTime is already prepared for it   Convert LocalDateTime to Time Zone ISO8601 String  LocalDateTime ldt   LocalDateTime now     ZonedDateTime zdt   ldt atZone ZoneOffset UTC     you might use a different zone String iso8601   zdt toString      Convert from ISO8601 String back to a LocalDateTime  String iso8601    2016-02-14T18 32 04 150Z   ZonedDateTime zdt   ZonedDateTime parse iso8601   LocalDateTime ldt   zdt toLocalDateTime

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All the answers are good  The java8  have these patterns for parsing and formatting timezone  V  z  O  X  x  Z  Here s they are  for parsing  according to rules from the documentation      Symbol  Meaning                     Presentation      Examples    ------  -------                     ------------      -------    V       time-zone ID                zone-id           America Los Angeles  Z  -08 30    z       time-zone name              zone-name         Pacific Standard Time  PST    O       localized zone-offset       offset-O          GMT 8  GMT 08 00  UTC-08 00     X       zone-offset  Z  for zero    offset-X          Z  -08  -0830  -08 30  -083015  -08 30 15     x       zone-offset                 offset-x           0000  -08  -0830  -08 30  -083015  -08 30 15     Z       zone-offset                 offset-Z           0000  -0800  -08 00   But how about formatting  Here s a sample for a date  assuming ZonedDateTime  that show these patters behavior for different formatting patters     The helper function  static void printInPattern ZonedDateTime dt  String pattern        System out println pattern    quot    quot    dt format DateTimeFormatter ofPattern pattern                   The date  String strDate    quot 2020-11-03 16 40 44 America Los Angeles quot   DateTimeFormatter format   DateTimeFormatter ofPattern  quot yyyy-MM-dd HH mm ss zzzz quot    ZonedDateTime dt   ZonedDateTime parse strDate  format      2020-11-03T16 40 44-08 00 America Los Angeles      Rules     printInPattern dt   quot V quot           exception  printInPattern dt   quot VV quot             America Los Angeles    printInPattern dt   quot VVV quot         exception     printInPattern dt   quot VVVV quot        exception  printInPattern dt   quot z quot              PST printInPattern dt   quot zz quot             PST printInPattern dt   quot zzz quot            PST printInPattern dt   quot zzzz quot           Pacific Standard Time printInPattern dt   quot O quot              GMT-8    printInPattern dt   quot OO quot          exception     printInPattern dt   quot OO0 quot         exception  printInPattern dt   quot OOOO quot           GMT-08 00 printInPattern dt   quot X quot              -08 printInPattern dt   quot XX quot             -0800 printInPattern dt   quot XXX quot            -08 00 printInPattern dt   quot XXXX quot           -0800 printInPattern dt   quot XXXXX quot          -08 00 printInPattern dt   quot x quot              -08 printInPattern dt   quot xx quot             -0800 printInPattern dt   quot xxx quot            -08 00 printInPattern dt   quot xxxx quot           -0800 printInPattern dt   quot xxxxx quot          -08 00 printInPattern dt   quot Z quot              -0800 printInPattern dt   quot ZZ quot             -0800 printInPattern dt   quot ZZZ quot            -0800 printInPattern dt   quot ZZZZ quot           GMT-08 00 printInPattern dt   quot ZZZZZ quot          -08 00  In the case of positive offset the   sign character is used everywhere where there is - now  and never omitted  This well works for new java time types  If you re about to use these for java util Date or java util Calendar - not all going to work as those types are broken and so marked as deprecated  please don t use them

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You can also use LocalDate parse   or LocalDateTime parse   on a String without providing it with a pattern  if the String is in ISO-8601 format   for example   String strDate    2015-08-04   LocalDate aLD   LocalDate parse strDate   System out println  Date      aLD    String strDatewithTime    2015-08-04T10 11 30   LocalDateTime aLDT   LocalDateTime parse strDatewithTime   System out println  Date with Time      aLDT     Output   Date  2015-08-04 Date with Time  2015-08-04T10 11 30   and use DateTimeFormatter only if you have to deal with other date patterns   For instance  in the following example  dd MMM uuuu represents the day of the month  two digits   three letters of the name of the month  Jan  Feb  Mar       and a four-digit year   DateTimeFormatter dTF   DateTimeFormatter ofPattern  dd MMM uuuu    String anotherDate    04 Aug 2015   LocalDate lds   LocalDate parse anotherDate  dTF   System out println anotherDate     parses to     lds     Output  04 Aug 2015 parses to 2015-08-04   also remember that the DateTimeFormatter object is bidirectional  it can both parse input and format output   String strDate    2015-08-04   LocalDate aLD   LocalDate parse strDate   DateTimeFormatter dTF   DateTimeFormatter ofPattern  dd MMM uuuu    System out println aLD     formats as     dTF format aLD      Output  2015-08-04 formats as 04 Aug 2015    see complete list of Patterns for Formatting and Parsing DateFormatter     Symbol  Meaning                     Presentation      Examples   ------  -------                     ------------      -------    G       era                         text              AD  Anno Domini  A    u       year                        year              2004  04    y       year-of-era                 year              2004  04    D       day-of-year                 number            189    M L     month-of-year               number text       7  07  Jul  July  J    d       day-of-month                number            10     Q q     quarter-of-year             number text       3  03  Q3  3rd quarter    Y       week-based-year             year              1996  96    w       week-of-week-based-year     number            27    W       week-of-month               number            4    E       day-of-week                 text              Tue  Tuesday  T    e c     localized day-of-week       number text       2  02  Tue  Tuesday  T    F       week-of-month               number            3     a       am-pm-of-day                text              PM    h       clock-hour-of-am-pm  1-12   number            12    K       hour-of-am-pm  0-11         number            0    k       clock-hour-of-am-pm  1-24   number            0     H       hour-of-day  0-23           number            0    m       minute-of-hour              number            30    s       second-of-minute            number            55    S       fraction-of-second          fraction          978    A       milli-of-day                number            1234    n       nano-of-second              number            987654321    N       nano-of-day                 number            1234000000     V       time-zone ID                zone-id           America Los Angeles  Z  -08 30    z       time-zone name              zone-name         Pacific Standard Time  PST    O       localized zone-offset       offset-O          GMT 8  GMT 08 00  UTC-08 00     X       zone-offset  Z  for zero    offset-X          Z  -08  -0830  -08 30  -083015  -08 30 15     x       zone-offset                 offset-x           0000  -08  -0830  -08 30  -083015  -08 30 15     Z       zone-offset                 offset-Z           0000  -0800  -08 00      p       pad next                    pad modifier      1             escape for text             delimiter            single quote                literal                        optional section start            optional section end            reserved for future use            reserved for future use            reserved for future use

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Let s take two questions  example string  quot 2014-04-08 12 30 quot   How can I obtain a LocalDateTime instance from the given string   import java time format DateTimeFormatter import java time LocalDateTime  final DateTimeFormatter formatter   DateTimeFormatter ofPattern  quot yyyy-MM-dd HH mm quot       Parsing or conversion final LocalDateTime dt   LocalDateTime parse  quot 2014-04-08 12 30 quot   formatter   dt should allow you to all date-time related operations  How can I then convert the LocalDateTime instance back to a string with the same format   final String date   dt format formatter

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I found the it wonderful to cover multiple variants of date time format like this   final DateTimeFormatterBuilder dtfb   new DateTimeFormatterBuilder    dtfb appendOptional DateTimeFormatter ofPattern  yyyy-MM-dd HH mm ss SSSSSSSSS     appendOptional DateTimeFormatter ofPattern  yyyy-MM-dd HH mm ss SSSSSSSS     appendOptional DateTimeFormatter ofPattern  yyyy-MM-dd HH mm ss SSSSSSS     appendOptional DateTimeFormatter ofPattern  yyyy-MM-dd HH mm ss SSSSSS     appendOptional DateTimeFormatter ofPattern  yyyy-MM-dd HH mm ss SSSSS     appendOptional DateTimeFormatter ofPattern  yyyy-MM-dd HH mm ss SSSS         appendOptional DateTimeFormatter ofPattern  yyyy-MM-dd HH mm ss SSS         appendOptional DateTimeFormatter ofPattern  yyyy-MM-dd HH mm ss SS         appendOptional DateTimeFormatter ofPattern  yyyy-MM-dd HH mm ss S         parseDefaulting ChronoField HOUR OF DAY  0       parseDefaulting ChronoField MINUTE OF HOUR  0       parseDefaulting ChronoField SECOND OF MINUTE  0

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Parsing a string with date and time into a particular point in time  Java calls it an   Instant   is quite complicated  Java has been tackling this in several iterations  The latest one  java time and java time chrono  covers almost all needs  except Time Dilation        However  that complexity brings a lot of confusion   The key to understand date parsing is   Why does Java have so many ways to parse a date   There are several systems to measure a time  For instance  the historical Japanese calendars were derived from the time ranges of the reign of the respective emperor or dynasty  Then there is e g  UNIX timestamp  Fortunately  the whole  business  world managed to use the same  Historically  the systems were being switched from to  for various reasons  E g  from Julian calendar to Gregorian calendar in 1582  So  western  dates before that need to be treated differently  And of course the change did not happen at once  Because the calendar came from the headquarteds of some religion and other parts of Europe believed in other dieties  for instance Germany did not switch until the year 1700       and why is the LocalDateTime  ZonedDateTime et al  so complicated   There are time zones  A time zone is basically a  stripe   1  of the Earth s surface whose authorities follow the same rules of when does it have which time offset  This includes summer time rules  The time zones change over time for various areas  mostly based on who conquers whom  And one time zone s rules change over time as well  There are time offsets  That is not the same as time zones  because a time zone may be e g   Prague   but that has summer time offset and winter time offset  If you get a timestamp with a time zone  the offset may vary  depending on what part of the year it is in  During the leap hour  the timestamp may mean 2 different times  so without additional information  it can t be reliably converted  Note  By timestamp I mean  a string that contains a date and or time  optionally with a time zone and or time offset   Several time zones may share the same time offset for certain periods  For instance  GMT UTC time zone is the same as  London  time zone when the summer time offset is not in effect    To make it a bit more complicated  but that s not too important for your use case      The scientists observe Earth s dynamic  which changes over time  based on that  they add seconds at the end of individual years   So 2040-12-31 24 00 00 may be a valid date-time   This needs regular updates of the metadata that systems use to have the date conversions right  E g  on Linux  you get regular updates to the Java packages including these new data  The updates do not always keep the previous behavior for both historical and future timestamps  So it may happen that parsing of the two timestamps around some time zone s change comparing them may give different results when running on different versions of the software  That also applies to comparing between the affected time zone and other time zone   Should this cause a bug in your software  consider using some timestamp that does not have such complicated rules  like UNIX timestamp  Because of 7  for the future dates  we can t convert dates exactly with certainty  So  for instance  current parsing of 8524-02-17 12 00 00 may be off a couple of seconds from the future parsing    JDK s APIs for this evolved with the contemporary needs   The early Java releases had just java util Date which had a bit naive approach  assuming that there s just the year  month  day  and time  This quickly did not suffice  Also  the needs of the databases were different  so quite early  java sql Date was introduced  with it s own limitations  Because neither covered different calendars and time zones well  the Calendar API was introduced  This still did not cover the complexity of the time zones  And yet  the mix of the above APIs was really a pain to work with  So as Java developers started working on global web applications  libraries that targeted most use cases  like JodaTime  got quickly popular  JodaTime was the de-facto standard for about a decade  But the JDK did not integrate with JodaTime  so working with it was a bit cumbersome  So  after a very long discussion on how to approach the matter  JSR-310 was created mainly based on JodaTime    How to deal with it in Java s java time  Determine what type to parse a timestamp to  When you are consuming a timestamp string  you need to know what information it contains  This is the crucial point  If you don t get this right  you end up with a cryptic exceptions like  Can t create Instant  or  Zone offset missing  or  unknown zone id  etc    Unable to obtain OffsetDateTime from TemporalAccessor Unable to obtain ZonedDateTime from TemporalAccessor Unable to obtain LocalDateTime from TemporalAccessor Unable to obtain Instant from TemporalAccessor   Does it contain the date and the time    Does it have a time offset  A time offset is the  hh mm part  Sometimes   00 00 may be substituted with Z as  Zulu time   UTC as Universal Time Coordinated  or GMT as Greenwich Mean Time  These also set the time zone  For these timestamps  you use OffsetDateTime  Does it have a time zone  For these timestamps  you use ZonedDateTime  Zone is specified either by   name   Prague    Pacific Standard Time    PST    or  zone ID    America Los Angeles    Europe London    represented by java time ZoneId    The list of time zones is compiled by a  TZ database   backed by ICAAN   According to ZoneId s javadoc  The zone id s can also somehow be specified as Z and offset  I m not sure how this maps to real zones  If the timestamp  which only has a TZ  falls into a leap hour of time offset change  then it is ambiguous  and the interpretation is subject of ResolverStyle  see below  If it has neither  then the missing context is assumed or neglected  And the consumer has to decide  So it needs to be parsed as LocalDateTime and converted to OffsetDateTime by adding the missing info    You can assume that it is a UTC time  Add the UTC offset of 0 hours  You can assume that it is a time of the place where the conversion is happening  Convert it by adding the system s time zone  You can neglect and just use it as is  That is useful e g  to compare or substract two times  see Duration   or when you don t know and it doesn t really matter  e g  local bus schedule      Partial time information   Based on what the timestamp contains  you can take LocalDate  LocalTime  OffsetTime  MonthDay  Year  or YearMonth out of it    If you have the full information  you can get a java time Instant  This is also internally used to convert between OffsetDateTime and ZonedDateTime   Figure out how to parse it  There is an extensive documentation on DateTimeFormatter which can both parse a timestamp string and format to string   The pre-created DateTimeFormatters should cover moreless all standard timestamp formats  For instance  ISO INSTANT can parse 2011-12-03T10 15 30 123457Z   If you have some special format  then you can create your own DateTimeFormatter  which is also a parser    private static final DateTimeFormatter TIMESTAMP PARSER   new DateTimeFormatterBuilder       parseCaseInsensitive       append DateTimeFormatter ofPattern  yyyy-MM-dd T HH mm ss SX        toFormatter      I recommend to look at the source code of DateTimeFormatter and get inspired on how to build one using DateTimeFormatterBuilder  While you re there  also have a look at ResolverStyle which controls whether the parser is LENIENT  SMART or STRICT for the formats and ambiguous information   TemporalAccessor  Now  the frequent mistake is to go into the complexity of TemporalAccessor  This comes from how the developers were used to work with SimpleDateFormatter parse String   Right  DateTimeFormatter parse        gives you TemporalAccessor      No need for this  TemporalAccessor ta   TIMESTAMP PARSER parse  2011-    etc      But  equiped with the knowledge from the previous section  you can conveniently parse into the type you need   OffsetDateTime myTimestamp   OffsetDateTime parse  2011-12-03T10 15 30 123457Z   TIMESTAMP PARSER     You do not actually need to the DateTimeFormatter either  The types you want to parse have the parse String  methods   OffsetDateTime myTimestamp   OffsetDateTime parse  2011-12-03T10 15 30 123457Z      Regarding TemporalAccessor  you can use it if you have a vague idea of what information there is in the string  and want to decide at runtime    I hope I shed some light of understanding onto your soul     Note  There s a backport of java time to Java 6 and 7  ThreeTen-Backport  For Android it has ThreeTenABP    1  Not just that they are not stripes  but there also some weird extremes  For instance  some neighboring pacific islands have  14 00 and -11 00 time zones  That means  that while on one island  there is 1st May 3 PM  on another island not so far  it is still 30 April 12 PM  if I counted correctly

[java] How to parse/format dates with LocalDateTime? (Java 8)

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