Callback interface used by JdbcTemplate's query methods. Implementations of this interface perform the actual work of extracting results, but don't need to worry about exception handling. SQLExceptions will be caught and handled correctly by the JdbcTemplate class.
NOTE: this is simpler than the RowCallbackHandler/ResultReader that Spring uses. Probably it would be good to extend this to be more similar to Spring's way of doing things, as that is more capable.