How to set an expiration date in java

Question

I am trying to write some code to correctly set an expiration date given a certain date.

For instance this is what i have.

    Date lastSignupDate = m.getLastSignupDate();
    long expirationDate = 0;
    long milliseconds_in_half_year = 15778463000L;
    expirationDate = lastSignupDate.getTime() + milliseconds_in_half_year; 
    Date newDate = new Date(expirationDate);

However, say if i the sign up date is on 5/7/2011 the expiration date output i get is on 11/6/2011 which is not exactly half of a year from the given date. Is there an easier way to do this?

Answer 1

I would use the Calendar class - the add method will do this kind of thing perfectly.

http://download.oracle.com/javase/6/docs/api/java/util/Calendar.html

    Date date = new Date();
    Calendar cal = Calendar.getInstance();
    cal.setTime(date);
    cal.add(Calendar.MONTH, 6);

            java.util.Date expirationDate = cal.getTime();

    System.err.println(expirationDate);

Answer 2

Here's a simple suggestion using joda-time:

DateTime dt = new DateTime(lastSignupDate);
dt = dt.plusDays(DateTimeConstants.MILLIS_PER_DAY * 365 / 2);
// you can also use dt.plusDays(364 / 2);

You can also use a Calendar :

Calendar c = Calendar.getInstance();
c.setTime(lastSignupDate);
c.add(Calendar.MILLISECOND, MILLIS_PER_DAY * 365 / 2);
// or c.add(Calendar.DAY_OF_YEAR, 364 / 2);

Answer 3

tl;dr

java.time.LocalDate.of( 2011 , Month.MAY , 7 )
    .plusMonths( 6 )
    .toString()

2011-11-07

java.time

You are using date-time values, so you must account for issues such as time zones, anomalies, and leap year. But you only want a date without a time-of-day and without a time zone, so much easier if you use a date-only class rather than a date-with-time class.

The modern approach uses java.time rather than the troublesome legacy date-time classes.

if i the sign up date is on 5/7/2011 the expiration date output i get is on 11/6/2011 which is not exactly half of a year from the given date

The LocalDate class represents a date-only value without time-of-day and without time zone.

LocalDate ld = LocalDate.of( 2011 , Month.MAY , 7 ) ;

You can do math with the java.time classes. Look for plus… and minus… methods.

LocalDate sixMonthsLater = ld.plusMonths( 6 ) ;

Or pass the amount of time.

Period p = Period.ofMonths( 6 ) ;
LocalDate sixMonthsLater = ld.plus( p ) ;

See this code run live at IdeOne.com .

2011-05-07

2011-11-07

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About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date , Calendar , & SimpleDateFormat .

The Joda-Time project, now in maintenance mode , advises migration to the java.time classes.

To learn more, see the Oracle Tutorial . And search Stack Overflow for many examples and explanations. Specification is JSR 310 .

Where to obtain the java.time classes?

• Java SE 8 , Java SE 9 , and later
  • Built-in.
  • Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and Java SE 7
  • Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport .
• Android
  • Later versions of Android bundle implementations of the java.time classes.
  • For earlier Android, the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP… .

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval , YearWeek , YearQuarter , and more .

Answer 4

Do you really need an expiration-date, which is accurate to the millisecond?

I would implement it as 6 Months from x.

Jan. 1 => Jul 1
Sep. 28=> Feb 28
Sep. 29=> Feb 28
Sep. 30=> Feb 28
Oct. 1=>  Mar 1

Maybe you like to be generous, and say 'Mar 1' for 'Sep 29 and 30' too.

Answer 5

Here's an example of using Date with TimeUnit that's a little more readable:

long year = TimeUnit.MILLISECONDS.convert(365, TimeUnit.DAYS);
Date expiry = new Date(System.currentTimeMillis() + year);
System.out.println(expiry);

Shame it doesn't have year and day, look at GregorianCalendar or Jodatime for a better API.

Answer 6

<code>
Calendar calendar = Calendar.getInstance();
calendar.setTimeInMillis(new Date().getTime());
// 10 minutes expiration time
calendar.add(calendar.MINUTE, 10);
// prints 10 minutes ahead time  
System.out.println(new Date(calendar.getTime().getTime()));