I've executed following query: select t.date-t.date2 from table as t
The query should return a single row of type interval. Indeed, resultSet.getObject(1) returns a PGInterval instance with the correct value (the returned interval is 2 days and several hours).
When I call resultSet.getString(1) the string representation of interval is "2 days 14:08:55.8246". The problem arises when I call resultSet.getTimestamp(1). As I saw in org.postgresql.jdbc2.TimestampUtils.loadCalendar(GregorianCalendar cal, String s, String type) it fails to parse correctly the string, which is returned by resultSet.getString(1) call. since it expects only the "14:08:55.8246" part and does not expectthe "2 days " part. Please note that in case the interval between two dates is smaller than 24 hours everything works correctly.
This is important since, generic products such as Hibernate that work over different jdbc drivers, refer to the interval data type as a java.sql.Timestamp object and call getTimestamp(int) method on the resultset to get the instance.