Develop Reference

Java Calendar how to validate date

I'm trying to validate a given date, but it's not working how I would like it. The user inputs a date, and it gets parsed and passed to an array, and I'm trying to validate the date is a correct date(taking into account leap years, Feb, etc) without making the code extremely lengthy.
Calendar calendar = new GregorianCalendar(getValidYear(), getValidMonth() - 1, getValidDay());
if( validYear < 2010 )
{
throw new InvalidDateException("Year must be greater than 2009");
} else {
if(validMonth < 1 || validMonth > 12 )
{
throw new InvalidDateException("Month value must be greater than or equal to 1 or less than or eqaul to 12");
} else {
if(validDay > calendar.getActualMaximum(Calendar.DAY_OF_MONTH) || validDay <= 0)
{
throw new InvalidDateException(String.format ("Day value must be greater than 0 and less than or equal to %s ",
calendar.getActualMaximum(Calendar.DAY_OF_MONTH) ) );
}
}//end nested if month
}//end nested IF year
}
If I put 2018/02/33 in and have it print for the exception it shows the date as March 05, 2018 and Im not exactly sure where these numbers are coming from. The code to parse the date is
String dateGiven[] = validDate.split("/");
validYear = Integer.parseInt(dateGiven[0]);
validMonth = Integer.parseInt( dateGiven[1] );
validDay = Integer.parseInt( dateGiven[2] );
And when I build the string to show the date it prints correctly, but it is not working with Calendar and Im not sure what Im doing wrong. Any help is appreciated!

It would be easier to use Java 8 time features:
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy/MM/dd");
LocalDate date = LocalDate.parse("2018/02/33", formatter);
will result in a DateTimeException when date is invalid:
java.time.DateTimeException: Invalid value for DayOfMonth (valid values 1 - 28/31): 33

Calendar is lenient by default. Quoting from the documentation of its method setLenient:
With lenient interpretation, a date such as "February 942, 1996" will
be treated as being equivalent to the 941st day after February 1,
1996. With strict (non-lenient) interpretation, such dates will cause an exception to be thrown. The default is lenient.
If you want to receive an exception if an invalid date is set on the Calendar then use setLenient(false);.
Otherwise 2018/02/33 is going to be interpreted as 32 days after February 1, which is March 5.

Dealing with month names in different languages

I have input with dates in many differing formats. I'm basically trying to take all the different formats and standardize them into ISO 8601 format.
If the date contains a month name, e.g., March, then I'm using the following function to get the month number, e.g. 03.
month = String.valueOf(Month.valueOf(month.toUpperCase()).getValue());
Anyway, the problem I am having is that the month names are in many different languages, with no indication what language they will be. I'm getting the following error when running the above function:
Caused by: java.lang.IllegalArgumentException: No enum constant java.time.Month.AUGUSTI
at java.lang.Enum.valueOf(Enum.java:238)
at java.time.Month.valueOf(Month.java:106)
Is there any library that can deal with month names in many different languages, returning the numeric value, or even just translating the month name to English?
Here's a sample of the input date:
1370037600
1385852400
1356994800
2014-03-01T00:00:00
2013-06-01T00:00:00
2012-01-01
2012
May 2012
März 2010
Julio 2009

If you have no idea in what language the month name is, the only way is to loop through all the available values of java.util.Locale, use a java.time.format.DateTimeFormatter and try to parse the month until you find one that works:
String input = "März 2010";
// formatter with month name and year
DateTimeFormatter fmt = DateTimeFormatter.ofPattern("MMMM yyyy");
Month month = null;
for (Locale loc : Locale.getAvailableLocales()) {
try {
// set the locale in the formatter and try to get the month
month = Month.from(fmt.withLocale(loc).parse(input));
break; // found, no need to parse in other locales
} catch (DateTimeParseException e) {
// can't parse, go to next locale
}
}
if (month != null) {
System.out.println(month.getValue()); // 3
}
In the code above, the month will be Month.MARCH and the output will be 3.

validation to check date formatting is not working as expected

I have following code which checks for the valid format date
private void validateDate(String date){
try {
String validDate = "MM/dd/yyyy";
SimpleDateFormat format = new SimpleDateFormat(validDate);
format.setLenient(false);
Date theDate = new Date();
theDate = format.parse(date);
}
catch (Exception e) {
}
}
I am passing the date value as 06/25/20014. In this year format is wrong and I was expecting that it will throw exception and will go inside catch, but it never happens and it successfully passes the code format.parse(date); due to which my application is not throwing error.
I also debugged the line format.parse(date); and it returns "Fri Jul 31 00:00:00 MST 20015". I am not sure why that line is not throwing any exception.
Thanks for your help!!

In the standard date formats for SimpleDateFormat, the number 'y' 's doesn't necessarily correspond to the number of digits (it isn't a regex). One or two y's is an indicator for a 2 digit year (15, 98, etc.) and 3 or more y's is an indicator for the full year.

If this line did throw an exception, then your program would stop working after year 9999, which is not usually what you want. Sure, you do not expect your program to last this long, but people did not expect to last up to y2k either; so Java's choice not to block at any date seems reasonable.
If you want to check the year is between 1 and 9999, you can just write a if: (see related question I want to get Year, Month, Day, etc from Java Date to compare with Gregorian Calendar date in Java. Is this possible?)
Calendar cal = Calendar.getInstance();
cal.setTime(date);
if (cal.get(Calendar.YEAR) > 9999)
throw new RuntimeException("Blah");

This is actually documented behaviour (at least for the Gregorian calendar, which I assume you will be using unless you explicitely set it to a different calendar):
Year: If the formatter's Calendar is the Gregorian calendar, the
following rules are applied.
For formatting, if the number of pattern
letters is 2, the year is truncated to 2 digits; otherwise it is
interpreted as a number. For parsing, if the number of pattern letters
is more than 2, the year is interpreted literally, regardless of the
number of digits.
And yes, 20015 will probably be a valid year some day ;) If you want to check for exactly 4 digits, you might want to consider using a regular expression matching before parsing.

I can see that the provided date is valid (although 18k years ahead)
public static void validateDate(String date){
try {
String validDate = "MM/dd/yyyy";
SimpleDateFormat format = new SimpleDateFormat(validDate);
format.setLenient(false);
Date theDate = format.parse(date);
Calendar c = new GregorianCalendar();
c.setTime(theDate);
int year = c.get(Calendar.YEAR);
int month = c.get(Calendar.MONTH);
int day = c.get(Calendar.DAY_OF_MONTH);
int pos = c.get(Calendar.DAY_OF_WEEK);
if (Calendar.WEDNESDAY == pos)
System.out.print("day is Wednesday on " + year + "/" + (month+1) + "/" + day);
}
catch (Exception e) {
System.out.print("Inside exception block " + e);
}
}
prints: day is Wednesday on 20014/6/25
If you need some year validation you can add additional check
if (year > MAX_YEAR) {
// add error here
}
Here is DEMO

Java Best way to parse quarterly dates

I have a date as APR-JUN10 or APR-JUN 2010 and i need output as 2010-06-30 I need the best way to parse above date in java and should be flexible in adding more such format of dates. note: APR-JUN10 will not parse by any java api, we have to break down APR & JUN 10 and get date as 2010-06-30.

You need to firm up your requirements.
Currently all you have told us is that APR-JUN 2010 should translate to the last day of June.
But what about FEB-JUN 2010? Should that also translate to the last day of June? Or should it throw a parse exception due to not being a full quarter? What about JUL-JUN 2010, where the second month is before the first? What about MAY-JUL 2010 -- three months but perhaps your definition of "quarter" requires starts of January, April, July, October.
Once you have your own requirements down, you can get to work on the conversion.
It's unlikely that an existing DateFormat implementation will do this exact task for you. You're likely to need to parse the string in your own code.
If the only legal options are JAN-MAR, APR-JUN, JUL-SEP, OCT-DEC, then you just have a five-way switch statement to set the month and day on a Calendar object (the fifth way being a default: case that throws an exception.
If your requirement is more complex, then your code will need to be more complex. Breaking the string into parts using a regex would be a good first step.
Pattern patt = Pattern.compile("(.{3})-(.{3}) (\d+)");
Matcher matcher = patt.matcher(qaurterString);
if(! matcher.find() || m.groupCount() != 3) {
throw new ParseException(...)
}
String fromMonth = matcher.group(1);
String toMonth = matcher.group(2);
int year = Integer.parseInt(matcher.group(3));
I think you'll have to write parsing code from scratch, whatever you do. The neatest end result would for you to create a class that implements DateFormat.

String s = "APR-JUN10";
// validation of quarter part
String quarter = s.substring(0, 7);
if (
!quarter.equals("JAN-MAR") && !quarter.equals("APR-JUN")
&& !quarter.equals("JUL-SEP") && !quarter.equals("OCT-DEC")
) {
throw new IllegalArgumentException("Input is not a quarter date: " + s);
}
// text processing with preprocessing hack (substring(4))
SimpleDateFormat inputFormat = new SimpleDateFormat("MMMyy", Locale.ENGLISH);
inputFormat.setLenient(false);
Date date = inputFormat.parse(s.substring(4));
System.out.println(date);
// Output: Tue Jun 01 00:00:00 CEST 2010 [format chooses 1 as default day-of-month]
// Go to end of month/quarter
GregorianCalendar gcal = new GregorianCalendar();
gcal.clear();
gcal.setTime(date);
gcal.set(Calendar.DAY_OF_MONTH, gcal.getActualMaximum(Calendar.DAY_OF_MONTH));
// format as ISO-date
SimpleDateFormat outputFormat = new SimpleDateFormat("yyyy-MM-dd");
String output = outputFormat.format(gcal.getTime());
System.out.println(output); // 2010-06-30
For the input "APR-JUN 2010" you need the input format pattern "MMM yyyy", else the solution is the same. Of course, the proposed solution assumes that every input starts with JAN-MAR, APR-JUN, JUL-SEP or OCT-DEC (you wrote about quarters). If you want you can validate it before processing phase by mean of s.substring(0, 7) etc.
UPDATE: I have now added the validation feature, see code.

ignore any white space or new line in java date compare

I am trying to compare two dates in java. While the following code works fine, I would like to handle situations where there may be some alterations in the date format of the input dates.
For example, in the below code, the date format of the two dates are as yyyy/mm/dd hh:mm:ss am. But sometimes there are some additional white space/new line characters found in the input date and this causes exception.
java.text.ParseException: Unparseable date: "02/14/2013
07:00:00 AM"
The following is the code am trying to execute.
try
{
Date date1 = (Date)DATE_FORMAT_yyyy_mm_dd_hh_mm_ss.parse(slaTime); // usually the data comes as 2013/02/03 09:09:09 AM
Date date2 = (Date)DATE_FORMAT_yyyy_mm_dd_hh_mm_ss.parse(actualTime);// usually the data comes as 2013/02/03 09:06:09 AM
// a error occurs
if(date1.before(date2))
{
return "True";
}
else
{
return "False";
}
}
catch (ParseException e)
{
e.printStackTrace();
}
how to handle this?

One of the simplest solutions is to strip all whitespace from the String version of the date before you parse it. Alter your date format to not include any spaces (yyyy/MM/ddhh:mm:ssaaa), and use this to parse the stripped string.
final DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/ddhh:mm:ssaaa");
final String dateStr = "02/14/2013 07:00:00" +
"\n AM";
Date failingDate = dateFormat.parse(dateStr);
Date passingDate = dateFormat.parse(dateStr.replaceAll("\\s",""));

For Month in year Use M instead of m
Correct date format would be yyyy/MM/dd hh:mm:ss aaa. And If there is any additional space or new line then you must remove it other wise it will failed to parse your string to date, your should exact match with format .
I would suggest you to remove all space and new line character then parse it.
you can use format like - yyyy/MM/ddhh:mm:ssaaa where there is no space. And replaceAll your space and new Line with empty String.
Date date = new SimpleDateFormat("yyyy/MM/ddhh:mm:ssaaa").parse("2013/02/1407:00:00AM");
and you actual code could be like -
dateString = dateString.replaceAll("\\s","");
SimpleDateFormat("yyyy/MM/ddhh:mm:ssaaa").parse(dateString);