How can I convert the facebook post created_time to the time zone of the user?

Question

I am displaying Facebook posts in my Android application using the Facebook SDK. I have the created_time for each post in the format:

2012-01-04T12:28:52+0000

I was able to parse this into a Java Date object like so:

public static final String DATE_FORMAT = "yyyy-MM-dd'T'HH:mm:ss+SSSS";
public static Date parseDate(String str) {
    SimpleDateFormat sdf = new SimpleDateFormat(DATE_FORMAT);

    try {
        Date date = sdf.parse(str);
    } catch(ParseException e) {
        Log.w(TAG, "Unable to parse date string \"" + str + "\"");
    }
    return date;
  }

Then, I am attempting to display a message describing the time that has elapsed since the post was created using this method:

public static String timeAgoInWords(Date from) {
    Date now = new Date();
    long difference = now.getTime() - from.getTime();
    long distanceInMin = difference / 60000;

    if ( 0 <= distanceInMin && distanceInMin <= 1 ) {
        return "Less than 1 minute ago";
    } else if ( 1 <= distanceInMin && distanceInMin <= 45 ) {
        return distanceInMin + " minutes ago";
    } else if ( 45 <= distanceInMin && distanceInMin <= 89 ) {
        return "About 1 hour";
    } else if ( 90 <= distanceInMin && distanceInMin <= 1439 ) {
        return "About " + (distanceInMin / 60) + " hours ago";
    } else if ( 1440 <= distanceInMin && distanceInMin <= 2529 ) {
        return "1 day";
    } else if ( 2530 <= distanceInMin && distanceInMin <= 43199 ) {
        return (distanceInMin / 1440) + "days ago";
    } else if ( 43200 <= distanceInMin && distanceInMin <= 86399 ) {
        return "About 1 month ago";
    } else if ( 86400 <= distanceInMin && distanceInMin <= 525599 ) {
        return "About " + (distanceInMin / 43200) + " months ago";
    } else {
        long distanceInYears = distanceInMin / 525600;
        return "About " + distanceInYears + " years ago";
    }
}

The problem is that the create_time of the post is 6 hours ahead of my time (EST). So the timeAgoInWords method doesn't work correctly. Does Facebook always record the creation time of posts in UTC/GMT +1 hour?

What can I do to convert the creation time so that timeAgoInWords will work correctly for the current user's timezone, no matter where they are?

Answer 1

This is the code I use to convert a UTC time string to a localized time string. Note the key for conversion is to use the TimeZone methods getRawOffset(), inDaylightTime(...) and getDSTSavings().

Note my date format is slightly different to what you are using so you'll need to change it.

public String GetLocalDateStringFromUTCString(String utcLongDateTime) {
    SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    String localDateString = null;

    long when = 0;
    try {
        when = dateFormat.parse(utcLongDateTime).getTime();
    } catch (ParseException e) {
        e.printStackTrace();
    }
    localDateString = dateFormat.format(new Date(when + TimeZone.getDefault().getRawOffset() + (TimeZone.getDefault().inDaylightTime(new Date()) ? TimeZone.getDefault().getDSTSavings() : 0)));

    return localDateString;
}

Obviously you want a Date object so you just need to change this line...

localDateString = dateFormat.format(new Date(when + TimeZone.getDefault().getRawOffset() + (TimeZone.getDefault().inDaylightTime(new Date()) ? TimeZone.getDefault().getDSTSavings() : 0)));

...to...

Date localDate = new Date(when + TimeZone.getDefault().getRawOffset() + (TimeZone.getDefault().inDaylightTime(new Date()) ? TimeZone.getDefault().getDSTSavings() : 0));

...then you just need to change the return type of the method and return localDate.

Answer 2

        DateFormat df = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");
        df.setTimeZone(TimeZone.getTimeZone("**USER_TIME_ZONE**"));