TimeZoneTest.java

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

/**
 * This is a test indicating the timezone issue for a datebase which is in a timezone which observes
 * DST,
 * for example, America/Los_Angeles.
 *
 * @author leo
 *
 */
public class TimeZoneTest {
    static TimeZone ptTz = TimeZone.getTimeZone("America/Los_Angeles");
    static TimeZone bjTz = TimeZone.getTimeZone("GMT+08");
    static TimeZone utc = TimeZone.getTimeZone("UTC");
    static SimpleDateFormat ptFormatter = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");
    static SimpleDateFormat bjFormatter = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");
    static {
        ptFormatter.setTimeZone(ptTz);
        bjFormatter.setTimeZone(bjTz);
    }

    public static void main(String[] args) throws ParseException {

        System.out.println("from utc to bj time");
        // pst -> pdt
        System.out.println("pst -> pdt");
        testToBJ(utc, 2016, 2, 13, 9, 00, 00);
        testToBJ(utc, 2016, 2, 13, 10, 00, 00);
        testToBJ(utc, 2016, 2, 13, 11, 00, 00);

        // pdt -> pst
        System.out.println("pdt -> pst");
        testToBJ(utc, 2016, 10, 6, 9, 00, 00);
        testToBJ(utc, 2016, 10, 6, 10, 00, 00);
        testToBJ(utc, 2016, 10, 6, 11, 00, 00);

        System.out.println("\nfrom pt to bj time");
        // pst -> pdt
        System.out.println("pst -> pdt");
        testToBJ(ptTz, 2016, 2, 13, 1, 00, 00);
        // the problem.
        testToBJ(ptTz, 2016, 2, 13, 2, 00, 00);
        testToBJ(ptTz, 2016, 2, 13, 3, 00, 00);

        // pst -> pdt
        System.out.println("pdt -> pst");
        testToBJ(ptTz, 2016, 10, 6, 1, 00, 00);
        testToBJ(ptTz, 2016, 10, 6, 2, 00, 00);
        testToBJ(ptTz, 2016, 10, 6, 3, 00, 00);

    }

    /**
     * Simulate the process by which we parse a datetime input from UI, persist it into DB, and
     * render it as a datetime in GMT+08 on UI
     *
     * @param tz
     * @param year
     * @param month
     * @param day
     * @param hour
     * @param minute
     * @param sec
     * @throws ParseException
     */
    protected static void testToBJ(TimeZone tz, int year, int month, int day, int hour, int minute, int sec) throws ParseException {
        Calendar cal = Calendar.getInstance(tz);
        // -> PDT
        cal.set(year, month, day, hour, minute, sec);
        String inDB = ptFormatter.format(cal.getTime());

        Date dt1 = ptFormatter.parse(inDB);
        // render on UI
        String onUI = bjFormatter.format(dt1);

        String str = String.format("%s: %d-%d-%dT%d:%d:%d  -> DB: %s -> UI: %s", tz.getID(), year, month + 1, day, hour, minute, sec, inDB, onUI);
        System.out.println(str);
    }


}

The output is:

from utc to bj time
pst -> pdt
UTC: 2016-3-13T9:0:0  -> DB: 2016-03-13T01:00:00 -> UI: 2016-03-13T17:00:00
UTC: 2016-3-13T10:0:0  -> DB: 2016-03-13T03:00:00 -> UI: 2016-03-13T18:00:00
UTC: 2016-3-13T11:0:0  -> DB: 2016-03-13T04:00:00 -> UI: 2016-03-13T19:00:00
pdt -> pst
UTC: 2016-11-6T9:0:0  -> DB: 2016-11-06T01:00:00 -> UI: 2016-11-06T17:00:00
UTC: 2016-11-6T10:0:0  -> DB: 2016-11-06T02:00:00 -> UI: 2016-11-06T18:00:00
UTC: 2016-11-6T11:0:0  -> DB: 2016-11-06T03:00:00 -> UI: 2016-11-06T19:00:00

from pt to bj time
pst -> pdt
America/Los_Angeles: 2016-3-13T1:0:0  -> DB: 2016-03-13T01:00:00 -> UI: 2016-03-13T17:00:00
America/Los_Angeles: 2016-3-13T2:0:0  -> DB: 2016-03-13T03:00:00 -> UI: 2016-03-13T18:00:00
America/Los_Angeles: 2016-3-13T3:0:0  -> DB: 2016-03-13T03:00:00 -> UI: 2016-03-13T18:00:00
pdt -> pst
America/Los_Angeles: 2016-11-6T1:0:0  -> DB: 2016-11-06T01:00:00 -> UI: 2016-11-06T17:00:00
America/Los_Angeles: 2016-11-6T2:0:0  -> DB: 2016-11-06T02:00:00 -> UI: 2016-11-06T18:00:00
America/Los_Angeles: 2016-11-6T3:0:0  -> DB: 2016-11-06T03:00:00 -> UI: 2016-11-06T19:00:00

You can see, for the conversion from PT to BJ time, two different datetimes like 2016-03-13T02:00:00-08, 2016-03-13T02:00:00-07 are rendered as same datetime on UI.
Which is because a datetime in DB, for example, Mysql datetime datatype which missed the timezone info, will be parsed with system timezone.