Develop Reference

What is wrong with this java date formatter?

I'm trying to format the date you see as a String in the below code, to be able to have it as a LocalDateTime object, but I'm getting an exception, I'm following this guide https://mkyong.com/java8/java-8-how-to-convert-string-to-localdate/, but unfortunately it doesn't have and example like the date I have below, can someone please give me a hand here? I would really appreciate :)
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("EEEE MMM d hh:mm:ss zzz yyyy", Locale.US);
String date = "Wed Nov 18 00:00:00 COT 2020";
LocalDateTime localDateTime = LocalDateTime.parse(date, formatter);
System.out.println(localDateTime);
System.out.println(formatter.format(localDateTime));
I am getting:
java.time.format.DateTimeParseException: Text 'Wed Nov 18 00:00:00 COT
2020' could not be parsed at index 0

If you want round trip parsing/formatting with Zones try
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("EEE MMM dd HH:mm:ss zzz yyyy", Locale.US);
String date = "Wed Nov 18 00:00:00 COT 2020";
ZonedDateTime localDateTime = ZonedDateTime.parse(date, formatter);
System.out.println(localDateTime);
System.out.println(formatter.format(localDateTime));

To answer the question as asked in the title, What is wrong with this Java date formatter?
EEEE is for full name of the day of the week like Monday. For the abbreviation like Mon you need either E, EE or EEE.
As others have said, lower case hh is for clock hour within AM or PM from 01 through 12, so cannot parse your hour of 00. And even if it could, it would not provide enough information for the time of day. For hour of day from 00 though 23 you need upper case HH.
There’s a more basic problem that Basil Bourque already mentioned in a comment: The result of parsing a time zone abbreviation like COT is generally undefined. While COT may have only one definition, I don’t know, most of the most common abbreviations are ambiguous, and you don’t know what you get from parsing them.
As has also been mentioned your formatter cannot be used for formatting a LocalDateTime. A LocalDateTime hasn’t got any time zone. The formatter requires a time zone for the abbreviated time zone name, zzz. You may either format a ZonedDateTime, or you may modify the formatter to have an override zone using its withZone method.
A tip: When you don’t know why parsing fails, try formatting the expected value with the same formatter and compare the result to the string you are trying to parse. Most often the difference will lead you on the right track. Like this:
ZonedDateTime val = ZonedDateTime.of(
2020, 11, 18, 0, 0, 0, 0, ZoneId.of("America/Bogota"));
DateTimeFormatter formatter
= DateTimeFormatter.ofPattern("EEEE MMM d hh:mm:ss zzz yyyy", Locale.US);
String toBeParsed = "Wed Nov 18 00:00:00 COT 2020";
String formatted = val.format(formatter);
System.out.println("String to be parsed: " + toBeParsed);
System.out.println("Formatted string: " + formatted);
Output:
String to be parsed: Wed Nov 18 00:00:00 COT 2020
Formatted string: Wednesday Nov 18 12:00:00 COT 2020
The difference are Wednesday and 12, so it seems the bugs in the pattern are at EEEE and hh.
Your string seems to come out of the toString method of the outdated java.util.Date class. To parse the string from there see one of the answers linked to at the bottom. Or still better, get hold of the Date object, convert it to a modern Instant using its toInstant method and perform any further conversions from there. Or yet still better, stop using Date completely.
Links
How to parse the result from Date.toString():
Answer by Arvind Kumar Avinash
Answer by Arvind Kumar Avihash
Answer by Arvind Kumar Avinash
My answer
Answer by Basil Bourque
And of course the answer by Scary Wombat to this question

Parsing date format with timezone [duplicate]

This question already has answers here:
Java SimpleDateFormat Pattern for JavaScript Date
(4 answers)
Closed 5 years ago.
I'm trying to parse a date string with a GMT+100
new SimpleDateFormat("EEE MMM dd yyyy HH:mm:ss").parse("Thu Apr 23 2015 11:30:49 GMT+0100")
Comes out as
Thu Apr 23 11:30:49 UTC 2015
If I add z or Z or X to the format, it's unparseable. If I don't add it, it's off by the offset, one hour.
What is the right way to parse this date?
--
Update: this differs from Java SimpleDateFormat Pattern for JavaScript Date in two ways: 1) this question is pure java and would have accepted answers other than those using SimpleDateFormat (i.e. new Java 8 features), and 2) the solution here is different to the other question.

Your expresssion should be EEE MMM dd yyyy HH:mm:ss 'GMT'Z(including the quotes), so your code is as follows:
new SimpleDateFormat("EEE MMM dd yyyy HH:mm:ss 'GMT'Z").parse("Thu Apr 23 2015 11:30:49 GMT+0100")
HOW THIS WORKS
According to the docs, anything passed in between single quotes(') in SimpleDateFormat pattern is not interpolated, but is assumed be just a part of the date format to be ignored while parsing.
And the equivalent of +0100 in SimpleDateFormat pattern terms is Z

Confused with Converting the date with SimpleDateFormat [duplicate]

This question already has answers here:
How to convert "Mon Jun 18 00:00:00 IST 2012" to 18/06/2012?
(5 answers)
Closed 5 years ago.
I have a problem with date converting. I use the following program and I expect the output: 19.05.2017
But the output is: 05.00.2017
Can anybody help?
String t = "Fri May 19 00:00:00 CEST 2017";
Date d = new SimpleDateFormat("EEE MMM DD hh:mm:ss zzzz YYYY", Locale.US).parse(t);
String s = new SimpleDateFormat("dd.mm.yyyy").format(d).toString();
System.out.println(s);

A surprising result. The oldfashioned classes SimpleDateFormat and friends are full of surprises. This is meant as a negative thing.
Uppercase DD is day of year. Lowercase hh is hour of AM or PM (1 through 12). Uppercase YYYY is weekbased year (only useful with week number). So you are asking for a date that is a Friday in May and the 19th day of the year. Obviously this is not possible.
The result of parsing is Thu Jan 05 23:00:00 CET 2017. Apparently SimpleDateFormat opts for giving you a Friday and for using the zone offset of 2 hours implied by CEST even though the date it has chosen is not at the time of year where CEST (summer time) is in use. I don’t know whether it just gives you the first Friday of the weekbased year (Friday in week 1 of the year). Friday at 0000 hours at offset GMT+2 equals Thursday at 23 at GMT+1, which is CET.
Next for the formatting, 05 is the date as expected, but lowercase mm means minutes. Since the minutes are 0, you get 00. You got the right year.
Rather than using the outdated classes that give you such surprises, I agree with Sam’s answer that you should use the newer classes in java.time:
ZonedDateTime dt = ZonedDateTime.parse(t,
DateTimeFormatter.ofPattern("EEE MMM dd HH:mm:ss zzz yyyy", Locale.US));
String s = dt.format(DateTimeFormatter.ofPattern("dd.MM.uuuu"));
This code gives you 19.05.2017 as you had expected. One of the good things about the modern classes is, if you try to parse with your original format pattern string, you will get a DateTimeParseException so you will know something is wrong. I certainly prefer an exception over incorrect output.
Another good thing is these classes respect the time zone in the input and use it in the output too (unless you explicitly instruct them otherwise). They will never turn Friday 6 January into Thursday 5 January because of some funny time zone issue.

Your input date is in Central European Summer Time and your date format is a bit wrong. Try
SimpleDateFormat input = new SimpleDateFormat("EEE MMM dd hh:mm:ss zzzz yyyy");
You might want to set the timezone on the output date format in order to get the date in the correct local time.
Ideally you'd move over to use a java.time style as shown here:
https://www.mkyong.com/java/java-convert-date-and-time-between-timezone/

TimeZone Conversion with SimpleDateFormat in Java

I have a SimpleDateFormat parser that parse in this way:
sdf = new java.text.SimpleDateFormat("yyyy-MM-DD HH:mm:ss z").parse("2013-10-25 17:35:14 EDT");
log.debug(sdf);
This give me Sat Jan 26 03:05:14 IST 2013
What am i missing here?

First of all, DD stands for day in year, You should use dd instead.
Also, if you want to print a date in a specific format, you need to use two SimpleDateFormats.
SimpleDateFormat.parse returns a Date object represents the date you specified at the given format.
The Date object itself is saved as a regular Date, no format attached to it.
If you want to print it in a specific format, you need to use another SimpleDateFormat and call format method.

you should use Format
SimpleDateFormat sdf1 = new java.text.SimpleDateFormat("yyyy-MM-dd HH:mm:SS z");
String sdf = sdf1.format(sdf1.parse("2013-10-25 17:35:14 EDT"));

There are two things.
sdf is an object of Date, which represents a specific instant in time (milliseconds elapsed since another instant known as "the epoch"). There is no format which is known to this object. And how this object is printed is solely handled by its class' toString method, which prints the date in this format:
dow mon dd hh:mm:ss zzz yyyy
This is exactly what you see in your output. Note that the timezone of the machine running the program is printed in this case. If you wish to print this object in a format of your choice you should use a DateFormat. To get output for a specific timezone you have to explicitly tell it to the DateFormat object (see below).
Another thing is you should be using dd instead of DD in the pattern. D is for day in year and d is for day in month, which I believe is what you want. Now keeping in mind both the points, this is one of the solutions to your problem:
DateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss z");
sdf.setTimeZone(TimeZone.getTimeZone("EDT")); // Time Zone for output
Date d = sdf.parse("2013-10-25 17:35:14 EDT");
System.out.println(sdf.format(d)); // You need format method
which outputs:
2013-10-25 17:35:14 EDT

What are the people answering not getting here is more the question:
2013-10-25 17:35:14 EDT != Sat Jan 26 03:05:14 IST 2013
I think it is because 'EDT' is the timezone and so, when it is 17:35 in EDT is is 3:05 in the UK, ignoring Daylight saving adjustments.

Java SimpleDateFormat parsing irregularities

I'm doing some date parsing in Java and am encountering some weird behavior.
I have a date string such as follows:
String s = "Sun Aug 11 2013 11:00:00 -0700 (Pacific Daylight Time)"
I'm trying to parse it into a date object like so:
SimpleDateFormat sdf = new SimpleDateFormat("EEE MMM dd yyyy HH:mm:ss Z (zzzz)");
I then print out the resulting date object from sdf.parse(s) and get:
Sun Aug 11 12:00:00 CDT 2013
I am in the central time zone, so it makes sense that it prints it as such, however, CDT is -0500, so the parsed date should be 13:00, not 12:00.
The odd thing is, if I remove either of the redundant pieces of time zone information, the date parses correctly. Using the format "EEE MMM dd yyyy HH:mm:ss Z ('Pacific Daylight Time')" or the format "EEE MMM dd yyyy HH:mm:ss '-0700' (zzzz)" results in the correct date:
Sun Aug 11 13:00:00 CDT 2013
This behavior seems to only occur with dates that fall within daylight savings time. If I instead parse a date in, say, December, with my initial date format, I get the correct result.
I have somewhat limited control over the format of the dates I'm parsing, and they could be coming from a variety of time zones. Has anyone encountered this behavior before, and is there a way to get around it without changing the format of the date string? I realize the time zone designations are redundant, but they aren't incorrect as far as I can tell.

There have certainly been bugs in Java's handling of daylight saving time and time zones in the past, and this sure looks like one you've found. What version of Java is this?
You might want to try giving Joda-Time a try to see if it handles the given date correctly.
If Joda doesn't help, you might need to try pre-parsing some of that date string to remove the descriptive time zone in parenthesis since it works when only one is defined. Very strange indeed!