如何将字符串转换为日期（HHMMMDD）（小时，月，日）

Question

I try to convert a string into date type. This is the whole what I did.

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("HHMMMDD");

String date = "23Mar25";

System.out.println(date);

LocalDate localDate = LocalDate.parse(date, formatter);

System.out.println(localDate);

And I got the error information as

Text '23Mar25' could not be parsed: 
Unable to obtain LocalDate from TemporalAccessor: 
{MonthOfYear=3, DayOfYear=25},ISO resolved to 23:00 of type 
java.time.format.Parsed at 
java.time.format.DateTimeFormatter.createError(DateTimeFormatter.java:1920)

Anyone can help me to solve it?

Answer 1

tl;dr

LocalTime.parse( "23Mar25" , DateTimeFormatter.ofPattern ( "HHMMMdd", Locale.US )
         .toString()  // 23:00

…and…

MonthDay.parse( "23Mar25" , DateTimeFormatter.ofPattern ( "HHMMMdd", Locale.US )
        .toString()   // --03-25

Details

If you are certain that input indeed represents an hour-of-day, month, and day-of-month…

DateTimeFormatter

Define a single DateTimeFormatter . Be sure to specify a Locale for the human language by which to translate the abbreviated name of the month.

String input = "23Mar25";
DateTimeFormatter f = DateTimeFormatter.ofPattern ( "HHMMMdd", Locale.US );

LocalTime

Use that formatter twice. Once to produce a time-of-day as a LocalTime object to hold the hour-of-day.

LocalTime lt = LocalTime.parse ( input, f );

MonthDay

Again to produce a MonthDay object to hold the month and the day-of-month.

MonthDay md = MonthDay.parse ( input , f  );

ZoneId

To make a specific moment of that value, we must assign a year and a time zone. If we want to use use the current year, we need a time zone for that as well. Keep in mind the fact that for any given moment both the date and the time-of-day vary around the globe by zone.

Specify a proper time zone name in the format of continent/region , such as America/Montreal , Africa/Casablanca , or Pacific/Auckland . Never use the 3-4 letter abbreviation such as EST or IST as they are not true time zones, not standardized, and not even unique(!).

ZoneId z = ZoneId.of ( "America/Montreal" ); 

LocalDate

Determine a LocalDate object by assigning a year to our MonthDay object.

int yearNumber = Year.now ( z )
                     .getValue ( ) ;
LocalDate ld = md.atYear ( yearNumber );

ZonedDateTime

Combine with the LocalTime to get an exact moment, a point on the timeline. Result is a ZonedDateTime object.

ZonedDateTime zdt = ZonedDateTime.of ( ld, lt, z );

Dump to console.

System.out.println ( "input: " + input );
System.out.println ( "lt: " + lt );
System.out.println ( "md: " + md );
System.out.println ( "ld: " + ld );
System.out.println ( "zdt: " + zdt );

input: 23Mar25

lt: 23:00

md: --03-25

ld: 2017-03-25

zdt: 2017-03-25T23:00-04:00[America/Montreal]

OffsetDateTime

If your input is intended for UTC , then instead of ZoneId and ZonedDateTime , use ZoneOffset.UTC constant and OffsetDateTime class in code similar to above.

OffsetDateTime zdt = OffsetDateTime.of ( ld, lt, ZoneOffset.UTC );

ISO 8601

Notice the output, the strings generated by the toString methods. The java.time classes use the ISO 8601 standard formats by default when parsing/generating strings. I strongly suggest you and your data-source use these standard formats rather than invent your own such as seen in the Question. The java.time classes can directly parse as well as generate such standard strings without needing to specify a formatting pattern.

To generate strings in other formats, use the DateTimeFormatter class. That topic is covered by many other Stack Overflow pages, so search for many examples and more discussion.

Answer 2

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("HHMMMDD");

It is using a pattern for:

HH: 2 spaces for hour
MMM: 3 spaces for month
DD: 2 spaces for day

I think you want a format like: `ddmmmyy

dd: 2 spaces for day
mmm: 3 spaces for month
yy: 2 spaces for year