Joda Time - Java date and time API

 Joda Time - Java date and time API

Almost any application we develop, we need to manipulate dates. Always we need convinent methods to manipulate time,format time.

Recently I started using JODA API,a free, open-source Java library for working with dates and times. This API is a replacement for Date and Calendar classes.JODA APU has no dependencies outside core Java classes

The Key concepts in JODA are

Instant
Represents the number of milliseconds from 1970-01-01T00:00Z
Classes represent instant in JODA are Instant,DateTime,DateMidNight


Instant myInstant = new Instant(1000); /* This Means 1 second after 1970*/
myInstant = instant.plus(100);
myInstant = instant.minus(50);

DateTime can be created like

DateTime startDate = new DateTime(2000, 1, 19, 0, 0, 0, 0);
DateTime endDate = new DateTime();

There are convinient methods provided in the API , like 

daysBetween,getYear,getMonthOfYear

Days d = Days.daysBetween(startDate, endDate);
int days = d.getDays();

System.out.println("  Difference between " + endDate);
System.out.println("  and " + startDate + " is " + days + " days.");

Formatting the output is also quite esay in DateTime. The pattern neede can be passed to the toString() method of DateTime

System.out.println(dateTime.toString("y-M-d HH:mm:ss.SSS a")); // Output will be 2010-3-11 10:46:08.994 AM
System.out.println(dateTime.toString("yyyy-MM-dd"));// Output will be 2010-03-11
System.out.println(dateTime.toString("yyyy/MM/dd"));// Output will be 2010/03/11
System.out.println(dateTime.toString("dd/MM/yyyy"));// Output will be 11/03/2010

DateFormatter could also be used for formatted printing
DateTimeFormatter monthAndYear = new DateTimeFormatterBuilder()
                .appendDayOfWeekText()
                // Week name
                .appendLiteral(' ')
                .appendMonthOfYearText()
                // Month
                .appendLiteral(' ')
                .appendDayOfMonth(2)
                //Day of month
                .appendLiteral(' ').appendYear(4, 4).appendLiteral(' ')
                .appendEraText().appendLiteral(' ').appendTimeZoneName()
                .toFormatter();

        System.out.println(monthAndYear.print(dateTime));
       
       
       
Partial

Some case we need is only the year/month/day, or the time of day, or even just the day of the week. Classes for dealing with time snippets are LocalDate and LocalTime

LocalDate localDate = SystemFactory.getClock().getLocalDate();
LocalTime localTime = SystemFactory.getClock().getLocalTime();

LocalDate localDate = new LocalDate(2010, 3, 10);// March 10, 2010
LocalTime localTime = new LocalTime(09, 30, 20, 0);

To have the Spans of time Joda provides three classes Duration,Period,Interval

The most interseting part of JODA is in Date calculations. For example if we need to add one week to the current time,

DateTime current = SystemFactory.getClock().getDateTime();
DateTime later = current.plusWeeks(1);

To add 50 days
DateTime current = SystemFactory.getClock().getDateTime();
DateTime later = now.plusDays(50);

Add 180 seconds from now:

DateTime current = SystemFactory.getClock().getDateTime();
DateTime later = now.plusSeconds(180);

Example using JODA Interval and Duration

private void intervalAndDuration() {

        DateTime start = new DateTime(1977, 3, 22, 0, 0, 0, 0);
        DateTime end =  new DateTime(2010, 1, 27, 0, 0, 0, 0);

        Interval interval = new Interval(start, end);
        start = interval.getStart();

        Duration duration = interval.toDuration(); 
        Period period = interval.toPeriod();
        // or
        Period weeks = interval.toPeriod(PeriodType.weeks());
        Period years = interval.toPeriod(PeriodType.years());
        Period days = interval.toPeriod(PeriodType.days());

        System.out.println("YEARS " + years.getYears() + " WEEKS "
                + weeks.getWeeks()/54 + " DAYS " + days.getDays()/365);
    }

Another simple AgeCalculator (Don't look for algorithm, method just to show useful methods in JODA API)

public void findAge(DateTime dateOfBirth, DateTime ageAsOn) {

        if (ageAsOn.isBefore(dateOfBirth.getMillis())) {
            System.out.println(" Wrong Dates !!! ");
            System.exit(0);
        }
        int startMonth, endMonth, startYear, endYear;
        int months, years;
        int totalDays = 0;

        startMonth = dateOfBirth.getMonthOfYear();
        endMonth = ageAsOn.getMonthOfYear();
        startYear = dateOfBirth.getYear();
        endYear = ageAsOn.getYear();

        //First calculate  the year
        if (endMonth >= startMonth)
            years = endYear - startYear;
        else
            years = endYear - startYear - 1;

        //Now calculate the months
        if (endMonth >= startMonth)
            months = endMonth - startMonth;
        else {
            if (ageAsOn.getDayOfMonth() > dateOfBirth.getDayOfMonth())
                months = (12 - startMonth) + endMonth - 1;
            else
                months = (12 - startMonth) + endMonth - 2;
        }

        //Now calculate the days
        if (endMonth != startMonth
                && ageAsOn.getDayOfMonth() != dateOfBirth.getDayOfMonth()) {
            if (ageAsOn.getDayOfMonth() > dateOfBirth.getDayOfMonth()) {
                totalDays = ageAsOn.getDayOfMonth()
                        - dateOfBirth.getDayOfMonth();
            } else {
                totalDays = (ageAsOn.getDayOfMonth() - 1)
                        - dateOfBirth.getDayOfMonth() + ageAsOn.getDayOfMonth();
            }
        }

String strAge = "Age as on " + ageAsOn.toString("dd-MM-yyyy") + " is "+ years + " years " + months + " month(s) " + totalDays+ " day(s)";
        System.out.println(strAge);

    }

 Useful Links
http://joda-time.sourceforge.net/
http://www.ibm.com/developerworks/java/library/j-jodatime.html