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How to convert Reactjs DateTimePicker date time convert to Java OffsetDateTime or LocalDateTime

My frontend ReactJs code snippet:-
import React, { useState } from 'react';
import DateTimePicker from 'react-datetime-picker';
import './App.css';
function App() {
const [value, onChange] = useState(new Date());
console.log("onChage: "+value);
return (
<div className="App">
<DateTimePicker
onChange={onChange}
value={value}
format={'dd/mm/yyyy hh:mm'}
/>
</div>
);
}
export default App;
I can see console log as
onChage: Thu Jul 21 2022 13:11:32 GMT+0300 (Eastern European Summer
Time)
I need to send this date time to Java Spingboot backend. For the backend I need to convert this date time to OffsetDateTime or LocalDateTime. How can I convert this?
Updated:
I tried and managed to convert to Data. By this:-
String dateStr = "Thu Jul 21 2022 13:11:32 GMT+0300 (Eastern European Summer Time)";
String[] tokens = dateStr.split("GMT");
String dateTimeStr = "";
if (tokens.length == 2){
dateTimeStr = tokens[0].trim();
}
System.out.println(dateTimeStr);
SimpleDateFormat formatter = new SimpleDateFormat("EEE MMM dd yyyy HH:mm:ss", Locale.ENGLISH);
Date date = formatter.parse(dateTimeStr);
String formattedDateString = formatter.format(date);
System.out.println("date: "+formattedDateString);
There I lost time zone and offset. How do I keep the time zone and offset GMT+0300 (Eastern European Summer Time)?

After the comment by Ole V.V. I mangaged to get both OffsetDateTime and ZonedDateTime. I am sharing the soluion. All credit goes to Ole V.V. Thanks a lot Ole V.V.
String dateStr = "Thu Jul 21 2022 13:11:32 GMT+0300 (Eastern European Summer Time)";
DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("EEE MMM d yyyy HH:mm:ss 'GMT'XX (zzzz)", Locale.ROOT);
OffsetDateTime date1 = OffsetDateTime.parse(dateStr, dateTimeFormatter);
System.out.println(date1);
// print 2022-07-21T13:11:32+03:00
ZonedDateTime zdt = ZonedDateTime.parse(dateStr, dateTimeFormatter.withZone(ZoneId.systemDefault()));
System.out.println(zdt);
// print 2022-07-21T13:11:32+03:00[Europe/Bucharest]

Simplest way to do is just do this :-
String timeString = input.substring(4,24);
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("MMM dd YYYY HH:mm:ss");
System.out.println(LocalDateTime.parse(timeString, formatter);

Parse datetime with offset string to LocalDateTime

I am trying to parse following datetime String to LocalDateTimeObject, however I am not able to identify the format of the datetime string.
Sat, 09 Oct 2021 02:10:23 -0400
String s = "Sat, 09 Oct 2021 02:10:23 -0400";
DateTimeFormatter formatter = DateTimeFormatter.ISO_OFFSET_DATE_TIME;
LocalDateTime dateTime = LocalDateTime.parse(s, formatter);
System.out.println(dateTime);
How should I determine the pattern of the above string?

You should first check if the date string matches any of the Predefined Formatters.
If not, then you have to make your own Formatter using .ofPattern(String pattern) or .ofPattern(String pattern, Locale locale). To do this, you can see all the defined pattern letters here in section Patterns for Formatting and Parsing.
For your example, you can use either DateTimeFormatter.RFC_1123_DATE_TIME:
DateTimeFormatter formatter = DateTimeFormatter.RFC_1123_DATE_TIME;
OffsetDateTime dateTime = OffsetDateTime.parse(s, formatted);
or:
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("EEE, dd MMM yyyy HH:mm:ss Z");
OffsetDateTime dateTime = OffsetDateTime.parse(s, formatted);
Note that OffsetDateTime is used to represent the date-time with an offset from UTC.
Symbol Meaning
------ -------
E day-of-week
d day-of-month
M month-of-year
y year-of-era
H hour-of-day (0-23)
m minute-of-hour
s second-of-minute
Z zone-offset

How to compare the datetime of format "EEE MMM dd HH:mm:ss zzz yyyy" and "yyyy-MM-dd hh:mm:sss" in java?

I have date of type "EEE MM DD HH:mm:ss zzz yyyy" (Wed Mar 04 03:34:45 GMT+08:00 2020) and "yyyy-MM-dd hh:mm:ss" (2020-02-04 02:10:58).How to compare this two date in java?
Both dates are in same timezone.

If you assume that the timezone of the second date is the same as for the first one then you can just use java.time. It has all parsing tools you need. Any other fixed timezone works as well.
Here is an example:
String a = "Wed Mar 04 03:34:45 GMT+08:00 2020";
String b = "2020-02-04 02:10:58";
ZonedDateTime parsedA;
ZonedDateTime parsedB;
DateTimeFormatter formatterA = DateTimeFormatter.ofPattern("EEE MMM dd HH:mm:ss zzz yyyy");
parsedA = ZonedDateTime.parse(a, formatterA);
DateTimeFormatter formatterB = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
parsedB = LocalDateTime.parse(b, formatterB).atZone(parsedA.getZone());
// What do you want to compare? For example you can tell if a is after b.
System.out.println(parsedA.isAfter(parsedB));
Have a look here if you need another format and need a listing of Pattern Letters and Symbols.

First of all these two dates are not comparable because of missing timezone in the second date.
Secondly, If you still want to do that with system's default time zone then you need to bring both the dates into common format.
Parse the dates into Date object and then you can play around it:
DateFormat dateFormat1 = new SimpleDateFormat("EEE MMM dd HH:mm:ss Z yyyy");
Date date1 = dateFormat1.parse("Wed Mar 04 03:34:45 GMT+08:00 2020");
DateFormat dateFormat2 = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
Date date2 = dateFormat2.parse("2020-02-04 02:10:58");
System.out.println(date1.after(date2));

There is a difference between time zone and time zone offset. The Date-Time string Wed Mar 04 03:34:45 GMT+08:00 2020 has a time zone offset, not a time zone. A time zone is unique and therefore it has an ID e.g. ZoneId.of("America/New_York") whereas a time zone offset tells you about the amount of time by which a given time is offset from the UTC time. There can be many time zones falling on the same time zone offset. Check List of tz database time zones to learn more about it. So, the most appropriate type to parse Wed Mar 04 03:34:45 GMT+08:00 2020 into is OffsetDateTime.
Since the second Date-Time string 2020-02-04 02:10:58 has neither a time zone nor a time zone offset, parse it into LocalDateTime.
Make sure to use Locale with the formatter because Date-Time parsing/formatting API is Locale-sensitive.
As long as the second Date-Time string refers to a Date-Time at the same timezone offset (i.e. GMT+08:00), you can do either of the two to compare them
Convert the first Date-Time string into LocalDateTime after parsing and then compare it with the second Date-Time string parsed into a LocalDateTime.
Convert the second Date-Time string into an OffsetDateTime after parsing and then compare it with the first Date-Time string parsed into an OffsetDateTime.
I would prefer the first approach as it is simpler. However, for the sake of completeness, I've shown below both approaches.
First approach:
DateTimeFormatter odtFormatter = DateTimeFormatter.ofPattern("EEE MMM dd HH:mm:ss O uuuu", Locale.ENGLISH);
OffsetDateTime firstOffsetDateTime = OffsetDateTime.parse("Wed Mar 04 03:34:45 GMT+08:00 2020", odtFormatter);
LocalDateTime firstLocalDateTime = firstOffsetDateTime.toLocalDateTime();
DateTimeFormatter ldtFormatter = DateTimeFormatter.ofPattern("uuuu-MM-dd HH:mm:ss", Locale.ENGLISH);
LocalDateTime secondLocalDateTime = LocalDateTime.parse("2020-02-04 02:10:58", ldtFormatter);
// Compare the two LocalDateTime values using isBefore, isAfter, equals etc.
if (firstLocalDateTime.isBefore(secondLocalDateTime)) {
// ...
}
Second approach:
DateTimeFormatter odtFormatter = DateTimeFormatter.ofPattern("EEE MMM dd HH:mm:ss O uuuu", Locale.ENGLISH);
OffsetDateTime firstOffsetDateTime = OffsetDateTime.parse("Wed Mar 04 03:34:45 GMT+08:00 2020", odtFormatter);
DateTimeFormatter ldtFormatter = DateTimeFormatter.ofPattern("uuuu-MM-dd HH:mm:ss", Locale.ENGLISH);
LocalDateTime secondLocalDateTime = LocalDateTime.parse("2020-02-04 02:10:58", ldtFormatter);
OffsetDateTime secondOffsetDateTime = secondLocalDateTime.atOffset(firstOffsetDateTime.getOffset());
// Compare the two OffsetDateTime values using isBefore, isAfter, equals etc.
if (firstOffsetDateTime.isBefore(secondOffsetDateTime)) {
// ...
}
I also prefer u to y with a DateTimeFormatter.
Learn more about the the modern date-time API from Trail: Date Time.

Parsing a DateTime in a time-zone

I have a date-time from Los_Angeles. The daylight saving applies when possible. I'm trying to convert that date-time into a timestamp, but I don't seem to understand the Java 8 DateTime API. The following snippet returns 1238112000 (which is the correct date if it was specified in UTC). What should I change to show 1238137200 instead?
String date = "March 27, 2009 00:00:00";
DateTimeFormatter formatter = DateTimeFormatter.
ofPattern("MMMM dd, yyyy HH:mm:ss", Locale.ENGLISH).
withZone(ZoneId.of("America/Los_Angeles"));
LocalDateTime.parse(date, formatter).toEpochSecond(ZoneOffset.UTC))

By parsing the date into a LocalDateTime, you are ignoring the timezone information from the formatter. You should use a ZonedDateTime:
public static void main(String[] args) {
String date = "March 27, 2009 00:00:00";
DateTimeFormatter formatter =
DateTimeFormatter.ofPattern("MMMM dd, yyyy HH:mm:ss", Locale.ENGLISH)
.withZone(ZoneId.of("America/Los_Angeles"));
long second = ZonedDateTime.parse(date, formatter).toEpochSecond();
System.out.println(second); // prints "1238137200"
}
On the returned instance, you can then call toEpochSecond().

Parse a Date of MMMM YYYY format

I have to parse a date string (e.g. "October 2015") to a Date.
So the question is: how can I parse a date of MMMM yyyy format? Its ok if the new Date object is the first month of the given month.
I tried:
DateTimeFormatter formatter = new DateTimeFormatterBuilder().appendPattern("MMMM yyyy").toFormatter();
TemporalAccessor ta = formatter.parse(node.textValue());
Instant instant = LocalDate.from(ta).atStartOfDay().atZone(ZoneId.systemDefault()).toInstant();
Date d = Date.from(instant);
But it does not work since the day is missing.

What you have there is a YearMonth, not a LocalDate since the day is missing.
The following works:
String string = "October 2015";
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("MMMM yyyy", Locale.ENGLISH);
YearMonth yearMonth = YearMonth.parse(string, formatter);
// Alternatively: YearMonth yearMonth = formatter.parse(string, YearMonth::from);
LocalDate date = yearMonth.atDay(1);
System.out.println(yearMonth); // prints "2015-10"
System.out.println(date); // prints "2015-10-01"
If you then want that as a java.util.Date, you need to specify which time zone you mean, maybe UTC or system default?
// ZoneId zone = ZoneOffset.UTC;
ZoneId zone = ZoneId.systemDefault();
Date javaUtilDate = Date.from(date.atStartOfDay(zone).toInstant());
System.out.println(javaUtilDate); // prints "Thu Oct 01 00:00:00 CEST 2015"
// because i'm in Europe/Stockholm.

How about this
DateFormat format = new SimpleDateFormat("MMMM yyyy", Locale.ENGLISH);
Date date = format.parse("October 2015");
System.out.println(date); // Prints Thu Oct 01 00:00:00 BST 2015

For java 8
DateTimeFormatter formatter = new DateTimeFormatterBuilder()
.appendPattern("MMMM yyyy")
.toFormatter(Locale.US);
TemporalAccessor ta = formatter.parse("October 2015");
YearMonth ym = YearMonth.from(ta);
LocalDateTime dt = LocalDateTime.of(ym.getYear(), ym.getMonthValue(),
1, 0, 0, 0);
Instant instant = Instant.from(dt.atZone(ZoneId.systemDefault()));
Date d = Date.from(instant);

You can use SimpleDateFormat's parse method for that
private static final SimpleDateFormat DATE_FORMAT = new SimpleDateFormat("MMMMM yyyy"); //MMMM yyyy example: October 2015
public Date getDateFromString(String input) {
return DATE_FORMAT.parse(input);
}
For more information, see: http://docs.oracle.com/javase/7/docs/api/java/text/SimpleDateFormat.html#parse(java.lang.String,%20java.text.ParsePosition)
Explanation of format:
MMMM indicates you are parsing full name months such as "October"
yyyy indicates you have 4-digit length years. If you wanted to parse for example, October 15, your format would look like this: "MMMM yy"

Why not use a SimpleDateFormatter?
This works fine for me:
SimpleDateFormat formatter = new SimpleDateFormat("MMMM yyyy");
Date d = formatter.parse("Oktober 2015");