All things Date and Time

import static java.time.temporal.TemporalAdjusters.firstDayOfYear;
import static java.time.temporal.TemporalAdjusters.lastDayOfYear;

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.TimeZone;

public class Time {
    public static void main(String[] argv) throws ParseException {
        //Get today's day of the year #1 method
        Calendar calendar = Calendar.getInstance();
        int dayOfYear = calendar.get(Calendar.DAY_OF_YEAR);
        System.out.println(dayOfYear);

        //Get today's day of the year #2 method
        int dayOfYear2 = LocalDate.now().getDayOfYear();
        System.out.println(dayOfYear2);


        System.out.println();


        //Create a specific date and time from scratch, add a day to it, then format it
        SimpleDateFormat monthDateFormat = new SimpleDateFormat("MM/dd");
        Calendar c = Calendar.getInstance();
        c.set(Calendar.YEAR, 2013);
        c.set(Calendar.MONTH, Calendar.JANUARY);
        c.set(Calendar.DATE, 1);
        c.set(Calendar.HOUR, 0);
        c.set(Calendar.MINUTE, 0);
        c.set(Calendar.SECOND, 0);
        c.set(Calendar.MILLISECOND, 0);

        c.add(Calendar.DATE, 22);
        Date startDate = c.getTime();
        String startDateMMdd = monthDateFormat.format(startDate);
        System.out.println(startDate);
        System.out.println(startDateMMdd);


        //Loop thru every day of a year
        for (int y = 0; y < 365; y++) {
            //System.out.println("y " + y);
            Calendar d = Calendar.getInstance();
            d.set(Calendar.YEAR, 2013);
            d.set(Calendar.MONTH, Calendar.JANUARY);
            d.set(Calendar.DATE, 1);
            d.set(Calendar.HOUR, 0);
            d.set(Calendar.MINUTE, 0);
            d.set(Calendar.SECOND, 0);
            d.set(Calendar.MILLISECOND, 0);
            d.add(Calendar.DATE, y);
            Date endDate = d.getTime();
            String endDateMMdd = monthDateFormat.format(endDate);
            //System.out.println(endDateMMdd);
        }


        System.out.println();


        //Get number of days in a month
        Calendar cal = Calendar.getInstance();
        cal.set(Calendar.YEAR, 2016);
        cal.set(Calendar.MONTH, 2);
        cal.set(Calendar.DAY_OF_MONTH, 1);
        cal.add(Calendar.DAY_OF_MONTH, -1);
        int lastdayOfMonth = cal.get(Calendar.DAY_OF_MONTH);
        System.out.println(lastdayOfMonth);

        //Loop thru all days in a month
        Calendar cal2 = Calendar.getInstance();
        cal2.set(Calendar.DAY_OF_MONTH, 1);
        int myMonth=cal2.get(Calendar.MONTH);

        while (myMonth==cal2.get(Calendar.MONTH)) {
            //System.out.print(cal.getTime());
            cal2.add(Calendar.DAY_OF_MONTH, 1);
        }


        System.out.println();


        //Convert day of year to day of month, printing the int day of month, and int day of week
        Calendar cal3 = Calendar.getInstance();
        cal3.set(Calendar.YEAR, 2007);
        cal3.set(Calendar.DAY_OF_YEAR, 100);
        System.out.println("Calendar date is: " + cal3.getTime());
        int dayOfMonth = cal3.get(Calendar.DAY_OF_MONTH);
        System.out.println("Calendar day of month: " + dayOfMonth);
        int dayOfWeek = cal3.get(Calendar.DAY_OF_WEEK);
        System.out.println("Calendar day of week: " + dayOfWeek);


        System.out.println();


        //Create a specific date based on day of year this year
        LocalDate localDateOfYear = LocalDate.now().withDayOfYear(12);
        System.out.println(localDateOfYear);


        System.out.println();


        //#1 method to get the last day of the year passed as a string, and format it. Also get the first day of year
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("MM/dd/yyyy");
        LocalDate start = LocalDate.parse("05/20/2013", formatter);
        LocalDate lastDay = start.with(lastDayOfYear());
        LocalDate firstDay = start.with(firstDayOfYear());
        String lastDayOfYear = formatter.format(lastDay);
        System.out.println(start);
        System.out.println(lastDay);
        System.out.println(lastDayOfYear);
        System.out.println(firstDay);


        System.out.println();


        //#2 method to get the last day of the year passed as a string. Also get the first day of year
        //Not as good, doesn't account for leap years
        Calendar cal4 = Calendar.getInstance();
        cal4.set(Calendar.DAY_OF_YEAR, 1);
        System.out.println(cal4.getTime().toString());
        cal4.set(Calendar.DAY_OF_YEAR, 366);
        System.out.println(cal4.getTime().toString());


        System.out.println();


        //Subtract years from a day, add days, and minus days
        DateTimeFormatter formatter2 = DateTimeFormatter.ofPattern("MM/dd/yyyy");
        LocalDate localDate = LocalDate.parse("01/31/2015", formatter2);
        LocalDate yearBefore = localDate.minusYears(2).plusDays(5).minusDays(1);
        System.out.println(yearBefore);


        System.out.println();


        //Compare two dates, checking if its equal, before, or after #1
        SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");

        Date currentDate = sdf.parse("04/28/2018");
        Date desiredDate = sdf.parse("10/21/2018");

        if (currentDate.before(desiredDate)) {
            System.out.println("currentDate is before desiredDate");
        }
        if (currentDate.equals(desiredDate)) {
            System.out.println("currentDate is equal to desiredDate");
        }
        else if (currentDate.after(desiredDate)) {
            System.out.println("currentDate is after desiredDate");
        }


        System.out.println();


        //Compare two dates, checking if its equal, before, or after #2
        SimpleDateFormat forexFormat = new SimpleDateFormat("MMM dd yyyy");

        Date todayForexDate = new Date();
        String todayDateStringFormatted = forexFormat.format(todayForexDate);

        Date forexDateParsed = forexFormat.parse("Mar 30 2010");
        Date todayDateParsed = forexFormat.parse(todayDateStringFormatted);

        long forexDiff = todayDateParsed.getTime() - forexDateParsed.getTime();

        if (forexDiff < 0) {
            System.out.println("BEFORE");
        }
        else if (forexDiff == 0) {
            System.out.println("EQUAL");
        }
        else if (forexDiff > 0) {
            System.out.println("AFTER");
        }



        //Convert date to day of week
        SimpleDateFormat format1 = new SimpleDateFormat("MM/dd/yyyy");
        Date dt1 = format1.parse("10/28/1995");
        DateFormat format2 = new SimpleDateFormat("EE");
        String finalDay = format2.format(dt1);
        System.out.println(finalDay);


        System.out.println();


        //Check if two dates are within a specific range of each other
        datesWithinRange("05/05/2018", "05/07/2018", -5, true);


        System.out.println();


        //Convert am/pm time to 24 hour
        SimpleDateFormat timeFormat = new SimpleDateFormat("hh:mma");
        SimpleDateFormat time24HFormat = new SimpleDateFormat("HH:mm");
        Date time1 = timeFormat.parse("6:30pm");
        String event24Hr = time24HFormat.format(time1);
        System.out.println(event24Hr);


        System.out.println();


        //Create a raw Calendar object and a raw Date object
        Calendar todayCal = Calendar.getInstance();
        Date todayDate = new Date();
        System.out.println(todayCal.getTime());
        System.out.println(todayDate);


        System.out.println();


        //Get difference in time between a date and now
        timeBetween();


        System.out.println();


        //Convert epoch value to usable timestamp
        long createDate = System.currentTimeMillis();
        Date date = new Date(createDate);
        DateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        format.setTimeZone(TimeZone.getTimeZone("Etc/UTC"));
        String formatted = format.format(date);
        System.out.println(formatted);
        format.setTimeZone(TimeZone.getTimeZone("US/Eastern"));
        formatted = format.format(date);
        System.out.println(formatted);


        System.out.println();


        //Use GregorianCalendar to get the current hour of the day in Los Angeles
        GregorianCalendar gc = new GregorianCalendar();
        int hour = gc.get(Calendar.HOUR_OF_DAY);
        gc.setTimeZone(TimeZone.getTimeZone("America/Los_Angeles"));
        hour = gc.get(Calendar.HOUR_OF_DAY);
        System.out.println("oncePerSchedule hour: " + hour);


        System.out.println();


        //Convert business day of year to overall day of year
        String firstDayOfYear = "Jan 01";
        SimpleDateFormat businessFormat = new SimpleDateFormat("MMM dd");
        Date businessFirstDay = businessFormat.parse(firstDayOfYear);
        System.out.println(calculateEndDate(businessFirstDay, 120));


        System.out.println();


        //Get number of business days between two Dates
        Date presentDate = new Date();
        SimpleDateFormat futureFormat = new SimpleDateFormat("MM/dd/yyyy");
        Date futureDate = futureFormat.parse("08/08/2020");
        System.out.println(calculateDuration(presentDate, futureDate));

    }


    private static boolean datesWithinRange(String currentDateString, String desiredDateString, int maxDayAmount, boolean absoluteRange) throws ParseException {
        SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");

        Date currentDate = sdf.parse(currentDateString);
        Date desiredDate = sdf.parse(desiredDateString);

        long diff = currentDate.getTime() - desiredDate.getTime();
        long diffDays = diff / (24 * 60 * 60 * 1000);

        if (maxDayAmount > 0) {
            if (diffDays >= 0 && diffDays <= maxDayAmount) {
                return true;
            }
        }
        else {
            if (diffDays <= 0 && diffDays >= maxDayAmount) {
                return true;
            }
            else if (absoluteRange && (diffDays >= 0 && diffDays <= Math.abs(maxDayAmount))) {
                return true;
            }
        }

        return false;
    }

    public static void timeBetween() {
        Date startDate = new Date();
        String dateStop = "06/12/2015 20:30:00";//"05/16/2015 09:00:00";

        SimpleDateFormat format = new SimpleDateFormat("MM/dd/yyyy HH:mm:ss");
        String dateStart = format.format(startDate);
        Date d1 = null;
        Date d2 = null;

        try {
            d1 = format.parse(dateStart);
            d2 = format.parse(dateStop);

            //in milliseconds
            long diff = d2.getTime() - d1.getTime();

            long diffSeconds = diff / 1000 % 60;
            long diffMinutes = diff / (60 * 1000) % 60;
            long diffHours = diff / (60 * 60 * 1000) % 24;
            long diffDays = diff / (24 * 60 * 60 * 1000);

            System.out.print(diffDays + " days, ");
            System.out.print(diffHours + " hours, ");
            System.out.print(diffMinutes + " minutes, ");
            System.out.print(diffSeconds + " seconds.");
            System.out.println("\n" + "total seconds " + (diff / 1000.0));
            System.out.println("total minutes " + (diff / (60 * 1000.0)));
            System.out.println("total hours " + (diff / (60 * 60 * 1000.0)));


        } catch (Exception e) {
            e.printStackTrace(); }
    }

    public static String calculateEndDate(Date startDate, int duration)
    {
        Calendar startCal = Calendar.getInstance();

        startCal.setTime(startDate);

        for (int i = 1; i < duration; i++)
        {
            startCal.add(Calendar.DAY_OF_MONTH, 1);
            while (startCal.get(Calendar.DAY_OF_WEEK) == Calendar.SATURDAY || startCal.get(Calendar.DAY_OF_WEEK) == Calendar.SUNDAY)
            {
                startCal.add(Calendar.DAY_OF_MONTH, 1);
            }
        }

        SimpleDateFormat monthDateFormat = new SimpleDateFormat("MMM dd");

        Date finalBizDay = startCal.getTime();
        String finalBixDayMMMdd = monthDateFormat.format(finalBizDay);

        return finalBixDayMMMdd;
    }

    public static int calculateDuration(Date startDate, Date endDate)
    {
        Calendar startCal = Calendar.getInstance();
        startCal.setTime(startDate);

        Calendar endCal = Calendar.getInstance();
        endCal.setTime(endDate);

        int workDays = 0;

        if (startCal.getTimeInMillis() > endCal.getTimeInMillis())
        {
            startCal.setTime(endDate);
            endCal.setTime(startDate);
        }

        do
        {
            startCal.add(Calendar.DAY_OF_MONTH, 1);
            if (startCal.get(Calendar.DAY_OF_WEEK) != Calendar.SATURDAY && startCal.get(Calendar.DAY_OF_WEEK) != Calendar.SUNDAY)
            {
                workDays++;
            }
        }
        while (startCal.getTimeInMillis() <= endCal.getTimeInMillis());

        return workDays;
    }
}