java - How to convert Gregorian string to Gregorian Calendar?

Question

I have to compute something based on the Calendar's date, but I am receiving the complete Gregorian Calendar's String value.

Eg i/p received {may be - "new GregorianCalendar().toString()"} as String :- java.util.GregorianCalendar[time=1410521241348,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=sun.util.calendar.ZoneInfo[id="Europe/London",offset=0,dstSavings=3600000,useDaylight=true,transitions=242,lastRule=java.util.SimpleTimeZone[id=Europe/London,offset=0,dstSavings=3600000,useDaylight=true,startYear=0,startMode=2,startMonth=2,startDay=-1,startDayOfWeek=1,startTime=3600000,startTimeMode=2,endMode=2,endMonth=9,endDay=-1,endDayOfWeek=1,endTime=3600000,endTimeMode=2]],firstDayOfWeek=1,minimalDaysInFirstWeek=1,ERA=1,YEAR=2014,MONTH=8,WEEK_OF_YEAR=37,WEEK_OF_MONTH=2,DAY_OF_MONTH=12,DAY_OF_YEAR=255,DAY_OF_WEEK=6,DAY_OF_WEEK_IN_MONTH=2,AM_PM=1,HOUR=0,HOUR_OF_DAY=12,MINUTE=27,SECOND=21,MILLISECOND=348,ZONE_OFFSET=0,DST_OFFSET=3600000]

I want to extract the Calendar's date value to process further computation.

Answer 1

You could find the time in the input string and convert it to a Gregorian Calendar. Then you would have to set its timezone as specified in the ZoneInfo field. Something like this might work:

    String calendarAsString="java.util.GregorianCalendar[time=1410521241348,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=sun.util.calendar.ZoneInfo[id="Europe/London",offset=0,dstSavings=3600000,useDaylight=true,transitions=242,lastRule=java.util.SimpleTimeZone[id=Europe/London,offset=0,dstSavings=3600000,useDaylight=true,startYear=0,startMode=2,startMonth=2,startDay=-1,startDayOfWeek=1,startTime=3600000,startTimeMode=2,endMode=2,endMonth=9,endDay=-1,endDayOfWeek=1,endTime=3600000,endTimeMode=2]],firstDayOfWeek=1,minimalDaysInFirstWeek=1,ERA=1,YEAR=2014,MONTH=8,WEEK_OF_YEAR=37,WEEK_OF_MONTH=2,DAY_OF_MONTH=12,DAY_OF_YEAR=255,DAY_OF_WEEK=6,DAY_OF_WEEK_IN_MONTH=2,AM_PM=1,HOUR=0,HOUR_OF_DAY=12,MINUTE=27,SECOND=21,MILLISECOND=348,ZONE_OFFSET=0,DST_OFFSET=3600000]";

    int timeStart=calendarAsString.indexOf("time=")+5;
    int timeEnd=calendarAsString.indexOf(',');
    String timeStr=calendarAsString.substring(timeStart, timeEnd);
    long timeInMillis=Long.parseLong(timeStr);

    int timezoneIdStart=calendarAsString.indexOf(""")+1;
    int timezoneIdEnd=calendarAsString.indexOf("",");
    String timeZoneStr=calendarAsString.substring(timezoneIdStart, timezoneIdEnd);

    System.out.println("time="+timeInMillis+" zone="+timeZoneStr);
    Calendar calendar=Calendar.getInstance(TimeZone.getTimeZone(timeZoneStr));
    calendar.setTimeInMillis(timeInMillis);

    System.out.println(calendarAsString);
    System.out.println(calendar);

or you can use a regular expression to do it, instead

    String regex="time=([0-9]*),.*ZoneInfo\[id="([^"]*)"";
    Pattern pattern=Pattern.compile(regex);
    Matcher matcher=pattern.matcher(calendarAsString);
    matcher.find();
    timeStr=matcher.group(1);
    timeInMillis=Long.parseLong(timeStr);
    timeZoneStr=matcher.group(2);
    System.out.println("time="+timeInMillis+" zone="+timeZoneStr);
    calendar=Calendar.getInstance(TimeZone.getTimeZone(timeZoneStr));
    calendar.setTimeInMillis(timeInMillis);
    System.out.println(calendar);

Note: if you just want the calendar's Date value, you can construct it from the timeInMillis, without having to reconstruct the whole GregorianCalendar object (and without having to find the timezone if you don't want to).

    Date date=new Date(timeInMillis);