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Converting Date to LocalDate returning strange results around 200AD

I'm getting inconsistent results when converting Dates to LocalDates, around the year 200. Using the following code to do the conversion:
private LocalDate toLocalDate(Date localDate)
{
return LocalDateTime.ofInstant(localDate.toInstant(), ZoneId.systemDefault()).toLocalDate();
}
My ZoneId.systemDefault() is Africa/Harare, which matches the CAT used in the test. The test case I run is
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("EEE MMM dd HH:mm:ss zzz yyyy", Locale.US);
String dateString = "Tue Jan 01 00:00:00 CAT 200";
String dateString2 = "Tue Jan 01 00:00:00 CAT 201";
String dateString3 = "Wed Dec 31 00:00:00 CAT 200";
System.out.println(toLocalDate(simpleDateFormat.parse(dateString)));
System.out.println(toLocalDate(simpleDateFormat.parse(dateString2)));
System.out.println(toLocalDate(simpleDateFormat.parse(dateString3)));
My expected output for this would be
0200-01-01
0201-01-01
0200-12-31
Or, if not that, at least consistently incorrect values. The actual results are
0199-12-31
0201-01-01
0200-12-31
So it seems that the first one is being rolled back slightly, possibly the two hours corresponding to the CAT timezone? But why does this only happen on the one case? Doing the same experiment with the year 2000 does not produce the same error.

Stephen has provided an explanation in the comment. Basically, java.util.Date uses a calendar system which cuts over between the Julian calendar system and the Gregorian calendar system in 1582, skipping 10 days. So dates in 1582 or before will exhibit discrepancies - but the size of the discrepancy will vary over time - by 3 days every 400 years, on average. It so happens that between 200 and 400AD, you don't see this because that corresponds to when the discrepancy is 0.
Here's a short but complete program to demonstrate the problem:
import java.time.*;
import java.util.*;
public class Test {
public static void main(String[] args) throws Exception {
// Value obtained with Noda Time: should be 0199-12-31T22:00:00Z.
long millis = -55855792800000L;
Instant instant = Instant.ofEpochMilli(millis);
Date date = new Date(millis);
System.out.println(instant);
System.out.println(date);
}
}
Output on my machine:
0199-12-31T22:00:00Z
Tue Jan 01 22:00:00 GMT 200
This is all complicated by the problems in your initial code of assuming CAT and Africa/Harare are the same (at that point in time, Africa/Harare is regarded as having an offset of +02:10) and the incorrect day names in your strings - but it's the bug in Java which is causing the issue here.
I suggest you perform all your parsing using the java.time.format classes - then I'd hope you won't get this inconsistency.

How to convert this unix time string to java date

I got this time string "2015-07-16T03:58:24.932031Z", I need to convert to a java timestamp, I use the following code, seems the converted date is wrong?
public static void main(String[] args) throws ParseException {
DateFormat format = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSSSS'Z'");
Date date = format.parse("2015-07-16T03:58:24.932031Z");
System.out.println("date: " + date);
System.out.println("timestamp: " + date.getTime());
}
output:
date: Thu Jul 16 04:13:56 CST 2015
timestamp: 1436991236031
Is my date format wrong?
Thanks in advance!

You don't want to quote the Z, it's a timezone indicator. Instead, use the X format specifier, for an ISO-8601 timezone.
Separately, you may want to pre-process the string a bit, because the part at the end, .932031, isn't milliseconds (remember, there are only 1000ms in a second). Looking at that value, it's probably microseconds (millionths of a second). SimpleDateFormat doesn't have a format specifier for microseconds. You could simply use a regular expression or other string manipulation to remove the last three digits of it to turn it into milliseconds instead.
This (which assumes you've done that trimming) works: Live Copy
DateFormat format = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSX");
// Note --------------------------------------------------------^^^^
Date date = format.parse("2015-07-16T03:58:24.932Z");
// Note trimming --------------------------------^
System.out.println("date: " + date);
System.out.println("timestamp: " + date.getTime());

Parse string to date using different formats/patterns

I need to parse a string to a date but have no prior knowledge which pattern the string will be in. This is similar to the question How to convert String to Date without knowing the format?.
To solve this I adopted couple of patterns to test the outcome. However, what I am getting is a bit strange.
Example 1:
import java.util.Date;
import org.apache.commons.lang3.time.DateUtils;
public Date extractDate(String dateStr) {
String [] datePatterns = {"yyyy-MM-dd", "dd-MM-yyyy"};
Date date = null;
try {
date = DateUtils.parseDate(dateStr, datePatterns);
}
catch (Exception except) {
except.printStackTrace();
}
return date;
}
public static void main(String[] args) throws Exception {
System.out.println ("2013-09-30:" + extractDate("2013-09-30") );
System.out.println ("30-09-2013:" + extractDate("30-09-2013") );
}
This gives:
2013-10-30:Wed Oct 30 00:00:00 EAT 2013
30-09-2013:Mon Mar 05 00:00:00 EAT 36
The result from parsing '30-09-2013' is obviously strange.
Example 2: Here I only switch the pattern
String [] datePatterns = {"dd-MM-yyyy", "yyyy-MM-dd"};
This gives:
2013-10-30:Mon Mar 05 00:00:00 EAT 36
30-09-2013:Mon Sep 30 00:00:00 EAT 2013
In example 2 the result from parsing '2013-10-30' is strange.
How can one parse date strings using different formats/patterns so that the resulting dates are correct?

Update to use parseDateStrictly. When I did this I got the following output:
2013-09-30:Mon Sep 30 00:00:00 EDT 2013
30-09-2013:Mon Sep 30 00:00:00 EDT 2013

My answer would be same. Without any prior knowledge of the format you can't parse date.
Few examples of writing a date would be: DD-MM-YYYY, MM-DD-YYYY, DD/MM/YYYY, MM/DD/YYYY, MM/DD/YY, DD/MM/YY. For only these many types of dates can you find any common pattern?
NO! Without knowing the format which user enters you can't parse it.
If you come up with pattern matching, a date such as 10-09-2010 which matches with MM-DD-YYYY format and DD-MM-YYYY format too. Here you will have a problem

Best efficient way to sort Months and Year in Java

I have a list which contains dates in format (MON-YYYY) in string format, I need to sort this list.The approach I have followed till now is reading the list and converting the string in date format and using compare option, but i am not getting the desired result
Code Snippet
List<String> abc = new ArrayList<String>();
List<Date> xyz = new ArrayList<Date>();
abc.add("JAN-2010");
abc.add("JAN-2011");
abc.add("APR-2013");
abc.add("NOV-2009");
try {
for (String abc1 : abc) {
Date date;
date = new SimpleDateFormat("MMM-yyyy", Locale.ENGLISH)
.parse(abc1);
xyz.add(date);
}
Collections.sort(xyz, new Comparator<Date>() {
public int compare(Date arg0, Date arg1) {
// return arg0.getDate().compareTo(o2.getDate());
return arg0.compareTo(arg1);
}
});
for (Date date1 : xyz) {
System.out.println("Sorted : " + date1);
}
} catch (ParseException e) {
e.printStackTrace();
}
}
Output
Sorted : Sun Nov 01 00:00:00 IST 2009
Sorted : Fri Jan 01 00:00:00 IST 2010
Sorted : Sat Jan 01 00:00:00 IST 2011
Sorted : Mon Apr 01 00:00:00 IST 2013
Expected Output
NOV-2009
JAN-2010
JAN-2011
APR-2013
I am also not sure if the above code is perfect in performance perspective as converting the string and parsing would take a long time if I have thousands of dates in MON-YYYY format in the list.

Ok, I see you corrected the typo.
Now, remember you need to use a DateFormatter also when you present the data, in addition to when you parse it.
So please try this:
for (Date date1 : xyz) {
System.out.println("Sorted : " + new SimpleDateFormat("MMM-yyyy", Locale.ENGLISH).format(date1));
}
You might want to make the SimpleDateFormat available to all methods of your class as a field.
Additional info: please be aware SimpleDateFormat is known to not be thread-safe. You can use ThreadLocal as one solution to that.
Good luck.

You've parsed your dateString to actual Date object. And java.util.Date can't be formatted. Only a String representation of that Date object can be got.
You need to change your comparator to compare your dateString format by internally converting the Strings to date.
If you are gonna sort the Date objects, you'll get the output you've got. Also, as mentioned by #darijan, change your logic in the comparator.

First i think it's better to have only one instance of SimpleDateFormat and always use this to parse your dates.
I also suggest to create this instance of SimpleDateFormat in front of your try block, so you solve your second problem and can use SimpleDateFormat.format(date) to parse your dates back to requested stringformat.

Working with Dates in Java

I need to work with dates and I wasn't sure how to go about that in Java since I have never done it before.
I am pulling dates from the Excel file and they can be retrieved in the Data format which would represent the date.
Ex:
2/1/2010
5/12/2011
8/15/2011
9/1/2011
9/1/2011
All my codes are pretty irrelvent to the question, but I am setting up a getter/setter method:
public Date getDate() {
return date;
}
public void setDate(Date date) {
this.date = date;
}
So my question is this, in what way when I am pulling the data from Excel:
temp.setDate((row.getCell(3).getDateCellValue());
I can set the limit so it only retrieves data from x amount of months. 8, 12, et.. from the last month/year displayed in the file, instead of going back all the way to 2010? I can provide more details if needed.
Edit: This is what I have now:
import java.util.Date;
Date date;
date = row.getCell(3).getDateCellValue();
It shows: Tue June 01 00:00:00
I don't care about Tuesday or 00:00:00, I just have a whole list of data and I only want to show x amount of months.
Edit: I figured it out. :)

The question is pretty vague, but if you are using Excel I have found it very beneficial to save the file as a 'filename.csv'. This format very easy to work with, it is comma delimited going across and newlines going down. If you are periodically checking the month, it would be easy to ensure that you only go x months backwards.

First you need to parse the dates accordingly using the SimpleDateFormat class. The result is a date object.
SimpleDateFormat df = new SimpleDateFormat( "M/d/yyyy" );
Date date = df.parse(row.getCell(3).getDateCellValue());
Then:
Calendar cal = Calendar.getInstance();
will return you an object ob type Calendar, where you can set the date by
cal.setTime(date);
Finally your loop reading the Excel file can determine according to the calendar object, if the date should be included / further processed by using:
int month = cal.get(Calendar.MONTH); // e.g. 11 for Nov
int year = cal.get(Calendar.YEAR); // e.g. 2011

You have to work with DateFormat.class fo parse the cell, or use a Calendar to put Day Month Year
EDIT
You can also use Calendar.class
final String[] tabDate = {"2/1/2010", "5/12/2011", "8/15/2011",
"9/1/2011", "9/1/2011"};
// Extract field's value
final Calendar c = Calendar.getInstance();
// Parse the list of stringDate
for (final String string : tabDate) {
System.out.println("Input string: " + string);
final String[] shortDate = string.split("/");
// Build Calendar
c.set(Integer.valueOf(shortDate[2]), Integer.valueOf(shortDate[0]),
Integer.valueOf(shortDate[1]));
// Extract date as you like
System.out.format("%25s : %d/%d/%d\t%s\n\n", c.getTime(),
c.get(Calendar.MONTH), c.get(Calendar.DATE),
c.get(Calendar.YEAR), c.getTimeInMillis());
}
Console :
Input string: 2/1/2010
Mon Mar 01 09:09:48 CET 2010 : 2/1/2010 1267430988109
Input string: 5/12/2011
Sun Jun 12 09:09:48 CEST 2011 : 5/12/2011 1307862588109
Input string: 8/15/2011
Thu Sep 15 09:09:48 CEST 2011 : 8/15/2011 1316070588109
Input string: 9/1/2011
Sat Oct 01 09:09:48 CEST 2011 : 9/1/2011 1317452988109
Input string: 9/1/2011
Sat Oct 01 09:09:48 CEST 2011 : 9/1/2011 1317452988109