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.
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:
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) ); 
java.sql.Timestamp class’ new features.Instant as seen in this Answer, you can apply a ZoneOffset to get an OffsetDateTime, or better, apply a ZoneId to get a ZonedDateTime. For more info, see my Answer and my diagram on another Question.
setTimestamp answer for more details.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 ) ; 