How to get a java.time object from a java.sql.Time

问题:

When retrieving a java.sql.Timestamp from a database via JDBC 4.1 or earlier, how does one obtain/convert to a java.time object?

Neither of the open-source JDBC drivers for Postgres is JDBC 4.2 compliant yet, so I'm looking for a way to use use java.time with JDBC 4.1.

回答1:

New Methods On Old Classes

By using the driver with Java 8 and later, you should automatically pick up some methods on your java.sql.Timestamp object for free. Both java.sql.Time and java.sql.Date have similar conversion methods.

Namely, to convert from java.sql to java.time you are looking for:

• Timestamp::toInstant()
• Timestamp::toLocalDateTime()
• Date::toLocalDate()
• Time::toLocalTime()

To go the other direction, from java.time to java.sql, use the new static methods:

• Timestamp.from(instant)
• Timestamp.valueOf(localDateTime)
• Date.valueOf(localDate)
• Time.valueOf(localTime)

Example:

preparedStatement.setTimestamp( 2, Timestamp.from(instant) );

回答2:

No need to convert

Like others have said in comments, PostgreSQL's JDBC driver now supports JDBC 4.2 including Java 8 Time API support. We can exchange java.time objects directly with the database.

https://jdbc.postgresql.org/documentation/head/8-date-time.html

So no need to convert, no need to ever use the java.sql types again. Use only their replacements in the java.time package as shown in this list.

PostgreSQL™                      Java SE 8 (java.time)
DATE                             LocalDate
TIME [ WITHOUT TIMEZONE ]        LocalTime
TIMESTAMP [ WITHOUT TIMEZONE ]   LocalDateTime
TIMESTAMP WITH TIMEZONE          OffsetDateTime or Instant

This can be retrieved via ResultSet::getObject

ResultSet rs = ...;
while (rs.next()) {
  LocalDate localDate = rs.getObject(1, LocalDate.class));
}

Store a java.time object by calling PreparedStatement::setObject.

myPreparedStatement.setObject( … , myInstant ) ;