按Java java.sql.Timestamp中的方式检索Oracle Date / Timestamp字段，而无需转换为DST

Question

I have column(LOGIN_TIME) in oracle with DATE datatype. I'm trying to read it as Timestamp in Java using JDBC. One of the rows in my table has a value of 2006-04-02 02:00:01.0 for this column. when I do

select LOGIN_TIME,CAST(LOGIN_TIME as TIMESTAMP) from TABLE;

I see that sql-developer shows the value as

2006-04-02 02:00:01.0

But when I retrieve this column value in Java using ResultSet.getTimestamp() method, I see the value as 2006-04-02 03:00:01.0.

After a lot of googling, I understood that

1. Firstly, 2006-04-02 02:00:01.0 is invalid/lost time as after 2006-04-02 01:59:00.0 the clock clicks 2006-04-02 03:00:00.0 due to daylight saving.
2. Oracle Date/Timestamp datatypes don't maintain time zones, hence Oracle accepted this value while inserting into DB without complaint.
3. However, since 02:00:01 is an invalid time, Java by default treat it leniently and converted the time to the assumed correct time of 03:00:01.

Now, my questions are

1. Why did java assume the correct time as 03:00:01? Is it dependent on any timezone, if yes, what is the default timezone? I don't think the default timezone here is UTC because

System.out.println(+rs.getTimestamp(index, Calendar.getInstance(TimeZone.getTimeZone("UTC"))));

gave me the value as

2006-04-01 18:00:01.0

2. How can I retrieve the value as is from Oracle without DST conversion by JDBC as 2006-04-02 02:00:01.0? or get it as 2006-04-02 03:00:01.0 and convert it back to original oracle value of 2006-04-02 02:00:01.0.

Answer 1

Date in Java does not store the timezone. Instead it uses your local timezone to represent values. That's why you see different results.

If you use Java 8 and JDBC 4.2 you may want to use a more reliable java.time.* package instead. It's simple as this:

LocalDateTime dateTime = rs.getObject(index, LocalDateTime.class);

If you want to convert LocalDateTime to java.util.Date , you can do it this way:

 Instant instant = dateTime.atZone(ZoneId.systemDefault()).toInstant();
 Date dateFromOld = Date.from(instant);