[Android]如何获取当前用户设置的时区

方法：TimeZone.getDefault().getDisplayName(true, TimeZone.SHORT);
获取的值如GMT+08:00,GMT-04:00,EDT 

另附：
国家码查询网址：http://www.chemie.fu-berlin.de/diverse/doc/ISO_3166.html
时区查询网址：https://en.wikipedia.org/wiki/List_of_tz_database_time_zones

说明：
参加源码TimeZone.java

public final String getDisplayName() {
        return getDisplayName(false, LONG, Locale.getDefault());
    }
   public final String getDisplayName(Locale locale) {
        return getDisplayName(false, LONG, locale);
    }
    public final String getDisplayName(boolean daylightTime, int style) {
        return getDisplayName(daylightTime, style, Locale.getDefault());
    }

    /**
     * Returns the {@link #SHORT short} or {@link #LONG long} name of this time
     * zone with either standard or daylight time, as written in {@code locale}.
     * If the name is not available, the result is in the format
     * {@code GMT[+-]hh:mm}.
     *
     * @param daylightTime true for daylight time, false for standard time.
     * @param style either {@link TimeZone#LONG} or {@link TimeZone#SHORT}.
     * @param locale the display locale.
     */
 public String getDisplayName(boolean daylightTime, int style, Locale locale) {
        if (style != SHORT && style != LONG) {
            throw new IllegalArgumentException("Bad style: " + style);
        }

        String[][] zoneStrings = TimeZoneNames.getZoneStrings(locale);
        String result = TimeZoneNames.getDisplayName(zoneStrings, getID(), daylightTime, style);
        if (result != null) {
            return result;
        }

        // If we get here, it's because icu4c has nothing for us. Most commonly, this is in the
        // case of short names. For Pacific/Fiji, for example, icu4c has nothing better to offer
        // than "GMT+12:00". Why do we re-do this work ourselves? Because we have up-to-date
        // time zone transition data, which icu4c _doesn't_ use --- it uses its own baked-in copy,
        // which only gets updated when we update icu4c. http://b/7955614 and http://b/8026776.

        // TODO: should we generate these once, in TimeZoneNames.getDisplayName? Revisit when we
        // upgrade to icu4c 50 and rewrite the underlying native code. See also the
        // "element[j] != null" check in SimpleDateFormat.parseTimeZone, and the extra work in
        // DateFormatSymbols.getZoneStrings.
        int offsetMillis = getRawOffset();
        if (daylightTime) {
            offsetMillis += getDSTSavings();
        }
        return createGmtOffsetString(true /* includeGmt */, true /* includeMinuteSeparator */,
                offsetMillis);
    }

public int getDSTSavings() {
    return useDaylightTime() ? 3600000 : 0;
}
/**
 * Returns the offset in milliseconds from UTC of this time zone's standard
 * time.
 */
public abstract int getRawOffset();