On 8 January 2011 00:05, Bob Jolliffe <[email protected]> wrote: > Hi all > > I have a small problem which I can't seem to get right. I am sure > Lars, Jo, Saptarshi and all ye java experts will know. Lars I guess > you are pretty familiar with the amplecode jdbc stuff. > > I have an interface and a class for iterating over a result set from a > query on the aggregatedatavalue table: > > the interface: > > package org.hisp.dhis.aggregation; > > public interface AggregatedDataValueStoreIterator { > > // ---------------------------------------------------------------------- > // AggregatedDataValueStoreIterator > // ---------------------------------------------------------------------- > > /** > * Gets the next AggregatedDataValue > * > * @return the aggregated value or null. > */ > AggregatedDataValue next(); > > /** > * Close any underlying resources > * > */ > void close(); > } > > and the class: > > public class JdbcAggregatedDataValueStoreIterator implements > AggregatedDataValueStoreIterator { > > private static final Log log = > LogFactory.getLog(AggregatedDataValueStoreIterator.class); > > static RowMapper<AggregatedDataValue> rowmapper = new > AggregatedDataValueRowMapper(); > > private ResultSet resultSet; > > public ResultSet getResultSet() { > return resultSet; > } > > public void setResultSet(ResultSet resultSet) { > this.resultSet = resultSet; > } > > private StatementHolder holder; > > public StatementHolder getHolder() > { > return holder; > } > > public void setHolder( StatementHolder holder ) > { > this.holder = holder; > } > > public JdbcAggregatedDataValueStoreIterator(ResultSet resultSet, > StatementHolder holder) { > this.resultSet = resultSet; > this.holder = holder; > } > > �...@override > public AggregatedDataValue next() { > AggregatedDataValue row = null; > try { > if (resultSet.next()) { > row = rowmapper.mapRow(resultSet); > } else { > this.close(); > } > } catch (SQLException ex) { > log.warn("Error reading aggregateddatavalue row: " + ex); > } > return row; > } > > �...@override > public void close() { > try { > if (!resultSet.isClosed()) { > resultSet.close(); > } > } catch (SQLException ex) { > log.warn("Error closing resultset: " + ex); > } > > holder.close(); > } > } > > This works very well, but now I also want to iterate over aggregate > indicator values. Now obviously I could just copy and paste the above > with minor adjustments, but it seems to makes sense to do this more > generically. 95% of the code in the class is pretty generic. What I > would like instead to have is an interface like: > > public interface StoreIterator<T> { > > // ---------------------------------------------------------------------- > // generic StoreIterator > // ---------------------------------------------------------------------- > > /** > * Gets the next object value > * > * @return the object value or null. > */ > T next(); > > /** > * Close any underlying resources > * > */ > void close(); > } > > That would be fine and dandy, but I can't implement the class > > public class JdbcStoreIterator<T> implements StoreIterator<T> > > by parameterizing the above JdbcAggregatedDataValueStoreIterator > class. The problem has to do with the rowmapper in the class. > > I can't say: > > static RowMapper<T> rowmapper = new AggregatedDataValueRowMapper(); > > because T is generic so I don't know the type of the rowmapper in > advance and the AggregateDataValueRowMapper (presumably like all the > other row mappers) is declared like: > > public class AggregatedDataValueRowMapper > implements RowMapper<AggregatedDataValue> > > In desperation I tried adding an extra type parameter to the > JdbcStoreIterator, like > > public class JdbcStoreIterator<T, R> implements StoreIterator<T> > > to pass in the rowmapper type, but it still defeats me - you can't > "simply" instantiate a new object based on a Type and various tricks > around Class<R> and getInstance() don't seem to work. > > Anybody have any good ideas of the best way to do this? Maybe I can > pass in a concrete RowMapper<T> into the JdbcStoreIterator<T> > constructor? Just thought of that now as a possibility and haven't > tried it.
OK I just answered my own question. That works. Pleased as a pig in sh**!. Sorry for the long email ... >I have to confess i have a much better understanding of C++ > generics than the Java variant, which is probably working against me > here :-( > > Failing which I will either return to copy and paste (which would have > taken all of half an hour instead of 3 hours puzzling over this) or > just do away with using the rowmapper at all and just program directly > to the jdbc resultset. > > Cheers > Bob > _______________________________________________ Mailing list: https://launchpad.net/~dhis2-devs Post to : [email protected] Unsubscribe : https://launchpad.net/~dhis2-devs More help : https://help.launchpad.net/ListHelp
