Find details at: http://monisiqbal.blogspot.com/2009/12/retrieving-time-zones-dst-information.html

TimeZoneDSTUtil.java

package open.source;

import java.io.Serializable;
import java.text.MessageFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.TimeZone;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Visit http://monisiqbal.blogspot.com
 * Follow me on: http://www.twitter.com/monisiqbal
 * @author monis.iqbal
 * 
 */
public class TimeZoneDSTUtil {

	/**
	 * DST details for the time zone i.e. when DST is applied and when it ends.
	 * @return
	 */
	public static String getDSTDetails(TimeZone timeZone) {
		
		if (timeZone.getDSTSavings() > 0) {
			/* Java's TimeZone related classes compute the start and end date of DST application but
			 * do not expose it. The only way is to decipher the toString method which fortunately
			 * prints enough information for us to deduce our required data.
			 */
			Pattern pattern = Pattern.compile("startMonth=(\\d+),startDay=(\\d+),.+endMonth=(\\d+),endDay=(\\d+),");
			Matcher m = pattern.matcher(timeZone.toString());
			if (m.find()) {
				Calendar startCal = Calendar.getInstance();
				Calendar endCal = Calendar.getInstance();
				
				startCal.set(Calendar.MONTH, Integer.valueOf(m.group(1)));
				startCal.set(Calendar.DAY_OF_MONTH, Integer.valueOf(m.group(2)));
				
				endCal.set(Calendar.MONTH, Integer.valueOf(m.group(3)));
				endCal.set(Calendar.DAY_OF_MONTH, Integer.valueOf(m.group(4)));
				
				final SimpleDateFormat monthFormatter = new SimpleDateFormat("MMMM");
				
				return new MessageFormat("Daylight savings starts at day {0} of {1}, ends at day {2} of {3}")
						.format(new Serializable[] {
								startCal.get(Calendar.DAY_OF_MONTH), monthFormatter.format(startCal.getTime()),
								endCal.get(Calendar.DAY_OF_MONTH), monthFormatter.format(endCal.getTime())
								}
						);
			}
		}
		
		return "NA";
	}
	
	/**
     * Prints out all available TimeZones in the JVM
     * 
     */
    public static void printAllTimeZoneDSTs() {
    	String[] availableIds = TimeZone.getAvailableIDs();
    	
    	for (String timeZoneId : availableIds) {
			printTimeZoneDST(timeZoneId);
		}
    }
    
    public static void printTimeZoneDST(String timeZoneId) {
    	TimeZone tz = TimeZone.getTimeZone(timeZoneId);
		System.out.println(tz.getID() + ", DST: " + getDSTDetails(tz));
    }
    
    public static void main(String[] args) {
    	
		//printAllTimeZoneDSTs();
		
		printTimeZoneDST("US/Pacific");
		printTimeZoneDST("US/Mountain");
		printTimeZoneDST("Brazil/East");
		printTimeZoneDST("Asia/Karachi");
	}
	
}