Useful Java date and time one liners and functions

dates.java

// get the current year as an int, E.G: 2018
Calendar.getInstance().get(Calendar.YEAR);

/* get date as iso 8601 string
 * public static Instant now()
 * Obtains the current instant from the system clock.
 * This will query the system UTC clock to obtain the current instant.
 * 
 * public String toString()
 * A string representation of this instant using ISO-8601 representation.
 * The format used is the same as DateTimeFormatter.ISO_INSTANT.
*/
Instant.now().toString();

Instant.now()                           // Capture the current moment in UTC with a resolution as fines nanoseconds but usually in microseconds or milliseconds.
       .truncatedTo(ChronoUnit.MINUTES) // Lop off any seconds or fractional second, to get a value in whole minutes.
       .toString();                     // Generate a String in standard ISO 8601 format where a `T` separates the year-month-day from the hour-minute-second, and the `Z` on the end for “Zulu” means UTC.

// java.util.Date date -> ISO 8601 string
Instant.ofEpochMilli(date.getTime()).toString();
String d = new Date().toInstant().toString();

ZonedDateTime.now(ZoneOffset.UTC).format(DateTimeFormatter.ISO_INSTANT);



public int getNumDaysInMonth(int month) {
    int year = Calendar.getInstance().get(Calendar.YEAR);
    YearMonth yearMonthObject = YearMonth.of(year, month);
    return yearMonthObject.lengthOfMonth();
}

// OffsetDateTime to Joda DateTime
private DateTime convertDate(OffsetDateTime offsetDateTime) {
    long epochMilli = offsetDateTime.toInstant().toEpochMilli();
    Date date = new Date(epochMilli);
    DateTime dateTime = new DateTime(date);
    return dateTime;
}