是特定于 java.sql.Timestamp 时区的吗？

我必须在 DB 中存储 UTC dateTime。
我已经将特定时区中给定的 dateTime 转换为 UTC。
我的输入 dateTime 是“2012122510:00:00 Z”时区是“ Asia/Calcutta”
我的服务器/数据库(Oracle)运行在同一时区(IST)“ Asia/Calcutta”< BR >

获取此特定时区中的 Date 对象

        String date = "20121225 10:00:00 Z";
String timeZoneId = "Asia/Calcutta";
TimeZone timeZone = TimeZone.getTimeZone(timeZoneId);


DateFormat dateFormatLocal = new SimpleDateFormat("yyyyMMdd HH:mm:ss z");
//This date object is given time and given timezone
java.util.Date parsedDate = dateFormatLocal.parse(date + " "
+ timeZone.getDisplayName(false, TimeZone.SHORT));


if (timeZone.inDaylightTime(parsedDate)) {
// We need to re-parse because we don't know if the date
// is DST until it is parsed...
parsedDate = dateFormatLocal.parse(date + " "
+ timeZone.getDisplayName(true, TimeZone.SHORT));
}


//assigning to the java.sql.TimeStamp instace variable
obj.setTsSchedStartTime(new java.sql.Timestamp(parsedDate.getTime()));

存入数据库

        if (tsSchedStartTime != null) {
stmt.setTimestamp(11, tsSchedStartTime);
} else {
stmt.setNull(11, java.sql.Types.DATE);
}

输出

DB (Oracle)存储了相同的给定 dateTime: "20121225 10:00:00，但不是以 UTC 格式存储的。

我已经从下面确认了。

     select to_char(sched_start_time, 'yyyy/mm/dd hh24:mi:ss') from myTable

我的数据库服务器也运行在同一时区“亚洲/加尔各答”

它给了我以下的表象

  1. Date.getTime()不是协调世界时
  2. 或者时间戳在存储到数据库时具有时区影响 我做错了什么？

还有一个问题:

timeStamp.toString()会像 java.util.date一样在本地时区打印吗? 不是 UTC？

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小开

It is specific from your driver. You need to supply a parameter in your Java program to tell it the time zone you want to use.

java -Duser.timezone="America/New_York" GetCurrentDateTimeZone

Further this: 

to_char(new_time(sched_start_time, 'CURRENT_TIMEZONE', 'NEW_TIMEZONE'), 'MM/DD/YY HH:MI AM')

May also be of value in handling the conversion properly. Taken from here

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最佳答案

Although it is not explicitly specified for setTimestamp(int parameterIndex, Timestamp x) drivers have to follow the rules established by the setTimestamp(int parameterIndex, Timestamp x, Calendar cal) javadoc:

Sets the designated parameter to the given java.sql.Timestamp value, using the given Calendar object. The driver uses the Calendar object to construct an SQL TIMESTAMP value, which the driver then sends to the database. With a Calendar object, the driver can calculate the timestamp taking into account a custom time zone. If no Calendar object is specified, the driver uses the default time zone, which is that of the virtual machine running the application.

When you call with setTimestamp(int parameterIndex, Timestamp x) the JDBC driver uses the time zone of the virtual machine to calculate the date and time of the timestamp in that time zone. This date and time is what is stored in the database, and if the database column does not store time zone information, then any information about the zone is lost (which means it is up to the application(s) using the database to use the same time zone consistently or come up with another scheme to discern timezone (ie store in a separate column).

For example: Your local time zone is GMT+2. You store "2012-12-25 10:00:00 UTC". The actual value stored in the database is "2012-12-25 12:00:00". You retrieve it again: you get it back again as "2012-12-25 10:00:00 UTC" (but only if you retrieve it using getTimestamp(..)), but when another application accesses the database in time zone GMT+0, it will retrieve the timestamp as "2012-12-25 12:00:00 UTC".

If you want to store it in a different timezone, then you need to use the setTimestamp(int parameterIndex, Timestamp x, Calendar cal) with a Calendar instance in the required timezone. Just make sure you also use the equivalent getter with the same time zone when retrieving values (if you use a TIMESTAMP without timezone information in your database).

So, assuming you want to store the actual GMT timezone, you need to use:

Calendar cal = Calendar.getInstance(TimeZone.getTimeZone("GMT"));
stmt.setTimestamp(11, tsSchedStartTime, cal);

With JDBC 4.2 a compliant driver should support java.time.LocalDateTime (and java.time.LocalTime) for TIMESTAMP (and TIME) through get/set/updateObject. The java.time.Local* classes are without time zones, so no conversion needs to be applied (although that might open a new set of problems if your code did assume a specific time zone).

小开

I think the correct answer should be java.sql.Timestamp is NOT timezone specific. Timestamp is a composite of java.util.Date and a separate nanoseconds value. There is no timezone information in this class. Thus just as Date this class simply holds the number of milliseconds since January 1, 1970, 00:00:00 GMT + nanos.

In PreparedStatement.setTimestamp(int parameterIndex, Timestamp x, Calendar cal) Calendar is used by the driver to change the default timezone. But Timestamp still holds milliseconds in GMT.

API is unclear about how exactly JDBC driver is supposed to use Calendar. Providers seem to feel free about how to interpret it, e.g. last time I worked with MySQL 5.5 Calendar the driver simply ignored Calendar in both PreparedStatement.setTimestamp and ResultSet.getTimestamp.

小开

For Mysql, we have a limitation. In the driver Mysql doc, we have :

The following are some known issues and limitations for MySQL Connector/J: When Connector/J retrieves timestamps for a daylight saving time (DST) switch day using the getTimeStamp() method on the result set, some of the returned values might be wrong. The errors can be avoided by using the following connection options when connecting to a database:

useTimezone=true
useLegacyDatetimeCode=false
serverTimezone=UTC

So, when we do not use this parameters and we call setTimestamp or getTimestamp with calendar or without calendar, we have the timestamp in the jvm timezone.

Example :

The jvm timezone is GMT+2. In the database, we have a timestamp : 1461100256 = 19/04/16 21:10:56,000000000 GMT

Properties props = new Properties();
props.setProperty("user", "root");
props.setProperty("password", "");
props.setProperty("useTimezone", "true");
props.setProperty("useLegacyDatetimeCode", "false");
props.setProperty("serverTimezone", "UTC");
Connection con = DriverManager.getConnection(conString, props);
......
Calendar nowGMT = Calendar.getInstance(TimeZone.getTimeZone("GMT"));
Calendar nowGMTPlus4 = Calendar.getInstance(TimeZone.getTimeZone("GMT+4"));
......
rs.getTimestamp("timestampColumn");//Oracle driver convert date to jvm timezone and Mysql convert date to GMT (specified in the parameter)
rs.getTimestamp("timestampColumn", nowGMT);//convert date to GMT
rs.getTimestamp("timestampColumn", nowGMTPlus4);//convert date to GMT+4 timezone

The first method returns : 1461100256000 = 19/04/2016 - 21:10:56 GMT

The second method returns : 1461100256000 = 19/04/2016 - 21:10:56 GMT

The third method returns : 1461085856000 = 19/04/2016 - 17:10:56 GMT

Instead of Oracle, when we use the same calls, we have :

The first method returns : 1461093056000 = 19/04/2016 - 19:10:56 GMT

The second method returns : 1461100256000 = 19/04/2016 - 21:10:56 GMT

The third method returns : 1461085856000 = 19/04/2016 - 17:10:56 GMT

NB : It is not necessary to specify the parameters for Oracle.

小开

You can use the below method to store the timestamp in database specific to your desired zone/zone Id.

ZonedDateTime zdt = ZonedDateTime.now(ZoneId.of("Asia/Calcutta")) ;
Timestamp timestamp = Timestamp.valueOf(zdt.toLocalDateTime());

A common mistake people do is use LocaleDateTime to get the timestamp of that instant which discards any information specif to your zone even if you try to convert it later. It does not understand the Zone.

Please note Timestamp is of the class java.sql.Timestamp.

小开

The answer is that java.sql.Timestamp is a mess and should be avoided. Use java.time.LocalDateTime instead.

So why is it a mess? From the java.sql.Timestamp JavaDoc, a java.sql.Timestamp is a "thin wrapper around java.util.Date that allows the JDBC API to identify this as an SQL TIMESTAMP value". From the java.util.Date JavaDoc, "the Date class is intended to reflect coordinated universal time (UTC)". From the ISO SQL spec a TIMESTAMP WITHOUT TIME ZONE "is a data type that is datetime without time zone". TIMESTAMP is a short name for TIMESTAMP WITHOUT TIME ZONE. So a java.sql.Timestamp "reflects" UTC while SQL TIMESTAMP is "without time zone".

Because java.sql.Timestamp reflects UTC its methods apply conversions. This causes no end of confusion. From the SQL perspective it makes no sense to convert a SQL TIMESTAMP value to some other time zone as a TIMESTAMP has no time zone to convert from. What does it mean to convert 42 to Fahrenheit? It means nothing because 42 does not have temperature units. It's just a bare number. Similarly you can't convert a TIMESTAMP of 2020-07-22T10:38:00 to Americas/Los Angeles because 2020-07-22T10:30:00 is not in any time zone. It's not in UTC or GMT or anything else. It's a bare date time.

java.time.LocalDateTime is also a bare date time. It does not have a time zone, exactly like SQL TIMESTAMP. None of its methods apply any kind of time zone conversion which makes its behavior much easier to predict and understand. So don't use java.sql.Timestamp. Use java.time.LocalDateTime.

LocalDateTime ldt = rs.getObject(col, LocalDateTime.class);
ps.setObject(param, ldt, JDBCType.TIMESTAMP);
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If your problem is to get a timestamp of the local zone, you can use this:

Timestamp.from(Instant.now()).toLocalDateTime()

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