Parsing Timezone String Date into Java's Instant

Question

I'm reading a from a few RSS sites which don't send the typical:

iso representation
- 2019-06-12T07:17:47Z - Instant.parse() can be used
RFC1123
- Wed, 12 Jun 2019 03:17:47 -0400 - DateTimeFormatter.RFC_1123_DATE_TIME.parse() can be used

Instead I'm getting these strings:

Tue, 25 May 2021 00:00:00 EDT
03 Jun 2021 18:35:00 HKT

I've already tried around with some custom patterns and the ZonedDateTime + OffsetDateTime parse() method. Although I haven't found a way to get a date time representation that I can convert into Instant. Neither do I control the source and can fix the output format.

How can I be more lenient and parse these date times?

Tue, 25 May 2021 00:00:00 EDT really conforms to RFC 1123 too. Only unfortunately Java’s implementation is limited: North American zone names … are not handled. (Doc) — Anonymous
– Anonymous, Commented Jun 6, 2021 at 17:09
@OleV.V. Alternative: My lib Time4J handles North American zone names. — Meno Hochschild
– Meno Hochschild, Commented Jun 7, 2021 at 10:50

Matt · Accepted Answer · 2021-06-06 18:53:24Z

5

You can create a DateTimeFormatter with a custom pattern that has an optional day-of-week at the beginning. Afterwards, use the parse method of formatter with which you can specify the desired type of the parsed date-time directly (as per comment of Ole V.V.). Another approach is to first parse as ZonedDateTime and then convert to an Instant.

DateTimeFormatter formatter =
        DateTimeFormatter.ofPattern("[EEE, ]dd MMM yyyy HH:mm:ss zzz", Locale.ENGLISH);

String input1 = "Tue, 25 May 2021 00:00:00 EDT";
Instant instant1 = formatter.parse(input1, Instant::from);
// Instant instant1 = ZonedDateTime.parse(input1, formatter).toInstant();
System.out.println(instant1);

String input2 = "03 Jun 2021 18:35:00 HKT";
Instant instant2 = formatter.parse(input2, Instant::from);
// Instant instant2 = ZonedDateTime.parse(input2, formatter).toInstant();
System.out.println(instant2);

Output:

2021-05-25T04:00:00Z
2021-06-03T10:35:00Z

edited Jun 6, 2021 at 18:53

answered Jun 6, 2021 at 15:40

Matt

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4 Comments

Arvind Kumar Avinash Over a year ago

Never use SimpleDateFormat or DateTimeFormatter without a Locale

Anonymous Over a year ago

Good answer. Possible alternative: Instant instant1 = formatter.parse(input1, Instant::from); (same for input2). Feels a bit simpler to me, but it’s a matter of taste. Nice and clever use of optional part for the day of week (the square brackets)!

Matt Over a year ago

@OleV.V. Thanks for sharing your alternative which I personally find better since no additional conversion from ZonedDateTime to Instant is necessary. I updated my answer accordingly.

Niklas Over a year ago

@Matt thanks a lot. Learned also about []. I've extended it to: [EEE, ]dd MMM yyyy HH:mm:ss zzz[Z] to be able to also parse dates such as Mon, 22 Mar 2021 18:39:18 GMT+0100. Thanks a lot!

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