一文彻底搞懂MySQL TimeStamp时区问题

    public String toString() {
        // "EEE MMM dd HH:mm:ss zzz yyyy";
        BaseCalendar.Date date = normalize();
        StringBuilder sb = new StringBuilder(28);
        int index = date.getDayOfWeek();
        if (index == BaseCalendar.SUNDAY) {
            index = 8;
        }
        convertToAbbr(sb, wtb[index]).append(' ');                        // EEE
        convertToAbbr(sb, wtb[date.getMonth() - 1 + 2 + 7]).append(' ');  // MMM
        CalendarUtils.sprintf0d(sb, date.getDayOfMonth(), 2).append(' '); // dd

        CalendarUtils.sprintf0d(sb, date.getHours(), 2).append(':');   // HH
        CalendarUtils.sprintf0d(sb, date.getMinutes(), 2).append(':'); // mm
        CalendarUtils.sprintf0d(sb, date.getSeconds(), 2).append(' '); // ss
        TimeZone zi = date.getZone();
        if (zi != null) {
            sb.append(zi.getDisplayName(date.isDaylightTime(), TimeZone.SHORT, Locale.US)); // zzz
        } else {
            sb.append("GMT");
        }
        sb.append(' ').append(date.getYear());  // yyyy
        return sb.toString();
    }

new Date().getTime();

Date date=new Date();
System.out.println(date.toString());
System.out.println(date.toLocaleString());//弃用
System.out.println(date.toGMTString());//弃用
//Thu Jul 14 23:55:10 CST 2022
//2022-7-14 23:55:10
//14 Jul 2022 15:55:10 GMT

sun.util.calendar.ZoneInfo[id="Asia/Shanghai",offset=28800000,dstSavings=0,useDaylight=false,transitions=31,lastRule=null]

//Java 中的 UTC和 GMT
jshell> Date now = new Date()
now ==> Thu Oct 30 16:59:27 CST 2021

jshell> import java.text.*

jshell> DateFormat df = DateFormat.getInstance()
df ==> java.text.SimpleDateFormat@ca92313f

jshell> df.setTimeZone(TimeZone.getTimeZone("GMT+8"))

jshell> df.format(now)
$5 ==> "2021/10/30 下午4:59

jshell> df.setTimeZone(TimeZone.getTimeZone("UTC+8"))

jshell> df.format(now)
$7 ==> "2021/10/30 上午8:59"

jshell> df.setTimeZone(TimeZone.getTimeZone("UTC"))

jshell> df.format(now)
$9 ==> "2021/10/30 上午8:59"

jshell> df.setTimeZone(TimeZone.getTimeZone("GMT"))

jshell> df.format(now)
$11 ==> "2021/10/30 上午8:59"

jshell> df.setTimeZone(TimeZone.getTimeZone("abc"))

jshell> df.format(now)
$13 ==> "2021/10/30 上午8:59"

//从上面的输出可以看出，在当前使用的 Java 版本中，设定时区偏移量时，是不能使用 UTC的，只能使用 GMT！另外，使用非法的时区 ID 时，会将时区设定为零时区。

//GMT+8和 Asia/Shanghai
//通常我们会将日期表示成格式化的字符串，如 2021-10-31 10:34:00，然后将其解析为日期类型并使用，需要打印时再将日期类型转换为字符串，例如：

jshell> import java.text.*

jshell> SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss")
sdf ==> java.text.SimpleDateFormat@4f76f1a0

jshell> DateFormat df = DateFormat.getInstance()
df ==> java.text.SimpleDateFormat@ca92313f

jshell> df.setTimeZone(TimeZone.getTimeZone("Asia/Shanghai"))

jshell> df.format(sdf.parse("2021-10-31 10:34:00"))
$6 ==> "2021/10/31 上午10:34"

jshell> df.setTimeZone(TimeZone.getTimeZone("GMT+8"))

jshell> df.format(sdf.parse("2021-10-31 10:34:00"))
$8 ==> "2021/10/31 上午10:34"

jshell> df.setTimeZone(TimeZone.getTimeZone("Asia/Shanghai"))

jshell> df.format(sdf.parse("1986-05-04 02:00:00"))
$10 ==> "1986/5/4 上午3:00"

jshell> df.setTimeZone(TimeZone.getTimeZone("GMT+8"))

jshell> df.format(sdf.parse("1986-05-04 02:00:00"))
$12 ==> "1986/5/4 上午2:00"

System.out.println(ZoneId.systemDefault());//Asia/Shanghai

    /**
     * Gets the system default time-zone.
     * <p>
     * This queries {@link TimeZone#getDefault()} to find the default time-zone
     * and converts it to a {@code ZoneId}. If the system default time-zone is changed,
     * then the result of this method will also change.
     *
     * @return the zone ID, not null
     * @throws DateTimeException if the converted zone ID has an invalid format
     * @throws ZoneRulesException if the converted zone region ID cannot be found
     */
    public static ZoneId systemDefault() {
        return TimeZone.getDefault().toZoneId();
    }

// 本地日期/时间
System.out.println("================本地时间================");
System.out.println(LocalDate.now());
System.out.println(LocalTime.now());
System.out.println(LocalDateTimenow());

// 时区时间
System.out.println("================带时区的时间ZonedDateTime================");
System.out.println(ZonedDateTime.now()); // 使用系统时区
System.out.println(ZonedDateTime.now(ZoneId.of("America/New_York"))); // 自己指定时区
System.out.println(ZonedDateTime.now(Clock.systemUTC())); // 自己指定时区
System.out.println("================带时区的时间OffsetDateTime================");
System.out.println(OffsetDateTime.now()); // 使用系统时区
System.out.println(OffsetDateTime.now(ZoneId.of("America/New_York"))); // 自己指定时区
System.out.println(OffsetDateTime.now(Clock.systemUTC())); // 自己指定时区

SHOW variables LIKE '%time_zone%';

Variable_name   |Value |
----------------+------+
system_time_zone|CST   |
time_zone       |SYSTEM|

    /**
     * Configures the client's timezone if required.
     * 
     * @throws CJException
     *             if the timezone the server is configured to use can't be
     *             mapped to a Java timezone.
     */
    public void configureTimezone() {
        String configuredTimeZoneOnServer = this.serverSession.getServerVariable("time_zone");

        if ("SYSTEM".equalsIgnoreCase(configuredTimeZoneOnServer)) {
            configuredTimeZoneOnServer = this.serverSession.getServerVariable("system_time_zone");
        }

        String canonicalTimezone = getPropertySet().getStringProperty(PropertyKey.serverTimezone).getValue();

        if (configuredTimeZoneOnServer != null) {
            // user can override this with driver properties, so don't detect if that's the case
            if (canonicalTimezone == null || StringUtils.isEmptyOrWhitespaceOnly(canonicalTimezone)) {
                try {
                    canonicalTimezone = TimeUtil.getCanonicalTimezone(configuredTimeZoneOnServer, getExceptionInterceptor());
                } catch (IllegalArgumentException iae) {
                    throw ExceptionFactory.createException(WrongArgumentException.class, iae.getMessage(), getExceptionInterceptor());
                }
            }
        }

        if (canonicalTimezone != null && canonicalTimezone.length() > 0) {
            this.serverSession.setServerTimeZone(TimeZone.getTimeZone(canonicalTimezone));

            //
            // The Calendar class has the behavior of mapping unknown timezones to 'GMT' instead of throwing an exception, so we must check for this...
            //
            if (!canonicalTimezone.equalsIgnoreCase("GMT") && this.serverSession.getServerTimeZone().getID().equals("GMT")) {
                throw ExceptionFactory.createException(WrongArgumentException.class, Messages.getString("Connection.9", new Object[] { canonicalTimezone }),
                        getExceptionInterceptor());
            }
        }

        this.serverSession.setDefaultTimeZone(this.serverSession.getServerTimeZone());
    }