问题

I'm being passed a date in ths format - "JAN01/2020" but I can't seem to find the DateTimeFormatter pattern for it. I tried these (as well as several others) but they're resulting in DateTimeParseException -

 DateTimeFormatter.ofPattern("MMMd/YYYY").parse("JAN01/2020")
 DateTimeFormatter.ofPattern("MMMdd/YYYY").parse("JAN01/2020")

I also considered this post's solution and the three lines below also result in DateTimeParseException. It does not appear to be a case-sensitivity issue Java 8 DateTimeFormatter for month in all CAPS not working

DateTimeFormatter formatter= DateTimeFormatter.ofPattern("MMMdd/yyyy");
LocalDateTime dateTime = LocalDateTime.parse("JAN14/2020", formatter);
System.out.println(dateTime.getYear());

I appreciate any suggestions!

回答1:

You may

handle the case with use of DateTimeFormatterBuilder
- .parseCaseInsensitive() for the case of the month, MMM is for Jan and you have JAN
- .appendPattern("MMMdd/yyyy") for the pattern
parse into a LocalDate as there is no time composant

DateTimeFormatterBuilder builder = new DateTimeFormatterBuilder().parseCaseInsensitive().appendPattern("MMMdd/yyyy");
DateTimeFormatter dateFormat = builder.toFormatter();

LocalDate dateTime = LocalDate.parse("JAN14/2020", dateFormat);
System.out.println(dateTime); // 2020-01-14

CODE DEMO

回答2:

Case-sensitive

The main problem with your format is, you are using YYYY instead of yyyy. Do it as follows:

import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeFormatterBuilder;

class Main {
    public static void main(String args[]) {
        DateTimeFormatter formatter = new DateTimeFormatterBuilder()
                                            .parseCaseInsensitive()
                                            .appendPattern("MMMd/yyyy")
                                            .toFormatter();
        System.out.println(LocalDate.parse("JAN01/2020", formatter));
    }
}

Output:

2020-01-01

Demo of using DateTimeFormatter::parse with it:

import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeFormatterBuilder;

class Main {
    public static void main(String args[]) {
        DateTimeFormatter formatter = new DateTimeFormatterBuilder()
                .parseCaseInsensitive()
                .appendPattern("MMMd/yyyy")
                .toFormatter();
        System.out.println(formatter.parse("JAN01/2020"));
    }
}

Output:

{},ISO resolved to 2020-01-01

回答3:

As the question you are linking to says, you need to use a DateTimeFormatterBuilder for case insensitive parsing of your month abbreviation in upper case.
Beware of the case of format pattern letters. yyyy and YYYY are different. See for example this question: Can't parse String to LocalDate (Java 8).

Supply a locale for your formatter. If JAN is English, then supply an English-speaking locale. For example:

    new DateTimeFormatterBuilder()
            .parseCaseInsensitive()
            .appendPattern("MMMdd/yyyy")
            .toFormatter(Locale.ENGLISH)

As azro said, since you haven’t got a time of day, parse into a LocalDate, not a LocalDateTime (or specify a default hour of day on the builder to be able to parse into a LocalDateTime, but I don’t see the advantage).

来源：https://stackoverflow.com/questions/62074063/what-pattern-of-datetimeformat-is-needed-for-datetimeformatter-to-parse-jan01-20

标签

java

datetime-format

java.time