Handling multiple formats in DateTimeFormatter

Question

I am developing using Java 8 a function that must handle the conversion from String to LocalDateTime of the following dates:

2019-06-20 12:18:07.207 +0000 UTC
2019-06-20 12:18:07.20 +0000 UTC
2019-06-20 12:18:07.2 +0000 UTC
2019-06-20 12:18:07 +0000 UTC

The strings are produced from an external library that I cannot change.

Following the suggestions given in the SO answer Optional parts in SimpleDateFormat, I tried using the optional formatting offered by the type DateTimeFormatter, using the characters [ and ]. I tried the following patterns:

yyyy-MM-dd HH:mm:ss[.S[S[S]]] Z z
yyyy-MM-dd HH:mm:ss[.S[S][S]] Z z

However, neither of them works.

Any suggestion?

score 5 · Accepted Answer · edited Aug 19 '19 at 14:56

5

You can build the pattern using DateTimeFormatterBuilder and reuse ISO_LOCAL_DATE and ISO_LOCAL_TIME constants:

    DateTimeFormatter formatter = new DateTimeFormatterBuilder()
            .append(DateTimeFormatter.ISO_LOCAL_DATE)
            .appendLiteral(" ")
            .append(DateTimeFormatter.ISO_LOCAL_TIME)
            .appendPattern("[ Z z]")
            .toFormatter();

    ZonedDateTime dt = ZonedDateTime.parse(date, formatter);

The trick is that DateTimeFormatter.ISO_LOCAL_TIME handles the different number of digit used to represent milliseconds its own. From DateTimeFormatter.ISO_LOCAL_TIME JavaDoc:

This returns an immutable formatter capable of formatting and parsing the ISO-8601 extended local time format. The format consists of:
[..]
One to nine digits for the nano-of-second. As many digits will be output as required.

edited Aug 19 '19 at 14:56

riccardo.cardin

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answered Aug 19 '19 at 11:48

Jaywalker

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Sorry, but your answer did not respond to my question. The optional and variable part is the milliseconds' block, not the offset. – riccardo.cardin Aug 19 '19 at 11:51
Doesn't ISO_LOCAL_TIME itself take care of that optional part of milliseconds? Try running the examples with this code. – Jaywalker Aug 19 '19 at 12:04
1

Yep, you're right. Sorry. I added some useful information to your answer. – riccardo.cardin Aug 19 '19 at 14:54
1

Thanks. You OK with ZonedDateTime, right? I think the requirement of having LocalDateTime in the question conflicts with zone specific text that needs to be parsed. – Jaywalker Aug 19 '19 at 14:59
Don't worry. The problem was with the optional part. – riccardo.cardin Aug 19 '19 at 15:06

Hassam Abdelillah · Answer 2 · 2019-08-19T14:05:03.247

I think it is better to use a DateTimeFormatterBuilder for that purpose. For the optional parts just use one of the follwing methods :

OptionalStart() & OptionalEnd()
Append your whole optional pattern with appendOptional()

Here is an example :

DateTimeFormatter formatter = DateTimeFormatter.ofPattern(""
    + "[yyyy-MM-dd HH:mm:ss.SSS Z z]"
    + "[yyyy-MM-dd HH:mm:ss.SS Z z]"
    + "[yyyy-MM-dd HH:mm:ss.S Z z]"
    + "[yyyy-MM-dd HH:mm:ss Z z]"
);

Also, you can create a dtf for each optional and append them with appendOptional() and the the DateTimeFormatterBuilder

for example :

DateTimeFormatter formatter = new DateTimeFormatterBuilder()
    .appendValue(HOUR_OF_DAY,2)
    .optionalStart()
    .appendValue(MINUTE_OF_HOUR,2)
    .optionalEnd()
    .optionalStart()
    .appendValue(SECOND_OF_MINUTE,2)
    .optionalEnd();
    .toFormatter();

This code is not tested but try to build your optional pattern each time in a start/end optional blocks.

In the first part of the answer, you cited the `DateTimeFormatterBuilder`, but you don't use it in the example. Can you modify the answer? — riccardo.cardin, Aug 19 '19 at 11:42
I added an brief example of how it may works with the builder, i didn't test it. Did the first way work? — Hassam Abdelillah, Aug 19 '19 at 14:05

Handling multiple formats in DateTimeFormatter

2 Answers2