计算夏令时的时间

ComputeSummerTime.java

package test.data;

import java.util.Calendar;
import java.util.Date;
import java.util.TimeZone;
import java.text.SimpleDateFormat;

public class ComputeSummerTime {

    /**
     * Dates those have not EXACTLY 24 hours ?
     **/
    public static void testDayTime(TimeZone timeZone) {

        SimpleDateFormat fmt = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

        System.out.println("Time Zone is " + timeZone.getDisplayName() + " " + timeZone.getID());

        Calendar start = Calendar.getInstance(timeZone);
        start.setTime(new Date(0));// UTC 1970-01-01

        System.out.println("start=" + fmt.format(start.getTime()));

        long end = Calendar.getInstance(timeZone).getTimeInMillis();// current time

        boolean find = false;
        for (long i = start.getTimeInMillis(); i < end; i = start.getTimeInMillis()) {
            start.add(Calendar.DATE, 1); // add one day

            if ((start.getTimeInMillis() - i) % (24 * 3600 * 1000L) != 0) {
                find = true;
                System.out.println("from " + fmt.format(new Date(i)) + " to " + fmt.format(start.getTime())
                        + " has " + (start.getTimeInMillis() - i) + "ms" + "["
                        + (start.getTimeInMillis() - i) / (3600 * 1000L) + "hours]");
            }
        }
        if (!find) {
            System.out.println("Every day is ok.");
        }
    }

    public static void main(String argv[]) throws Exception {

        TimeZone timeZone = TimeZone.getDefault();
        ComputeSummerTime.testDayTime(timeZone);

        System.out.println("----------------------------------------------------------------");

        timeZone = TimeZone.getTimeZone("GMT");
        ComputeSummerTime.testDayTime(timeZone);
    }

}