get next sequence value from database using hibernate

You can use Hibernate Dialect API for Database independence as follow

class SequenceValueGetter {    private SessionFactory sessionFactory;    // For Hibernate 3    public Long getId(final String sequenceName) {        final List<Long> ids = new ArrayList<Long>(1);        sessionFactory.getCurrentSession().doWork(new Work() {            public void execute(Connection connection) throws SQLException {                DialectResolver dialectResolver = new StandardDialectResolver();                Dialect dialect =  dialectResolver.resolveDialect(connection.getMetaData());                PreparedStatement preparedStatement = null;                ResultSet resultSet = null;                try {                    preparedStatement = connection.prepareStatement( dialect.getSequenceNextValString(sequenceName));                    resultSet = preparedStatement.executeQuery();                    resultSet.next();                    ids.add(resultSet.getLong(1));                }catch (SQLException e) {                    throw e;                } finally {                    if(preparedStatement != null) {                        preparedStatement.close();                    }                    if(resultSet != null) {                        resultSet.close();                    }                }            }        });        return ids.get(0);    }    // For Hibernate 4    public Long getID(final String sequenceName) {        ReturningWork<Long> maxReturningWork = new ReturningWork<Long>() {            @Override            public Long execute(Connection connection) throws SQLException {                DialectResolver dialectResolver = new StandardDialectResolver();                Dialect dialect =  dialectResolver.resolveDialect(connection.getMetaData());                PreparedStatement preparedStatement = null;                ResultSet resultSet = null;                try {                    preparedStatement = connection.prepareStatement( dialect.getSequenceNextValString(sequenceName));                    resultSet = preparedStatement.executeQuery();                    resultSet.next();                    return resultSet.getLong(1);                }catch (SQLException e) {                    throw e;                } finally {                    if(preparedStatement != null) {                        preparedStatement.close();                    }                    if(resultSet != null) {                        resultSet.close();                    }                }            }        };        Long maxRecord = sessionFactory.getCurrentSession().doReturningWork(maxReturningWork);        return maxRecord;    }}

Here is what worked for me (specific to Oracle, but using scalar seems to be the key)

Long getNext() {    Query query =         session.createSQLQuery("select MYSEQ.nextval as num from dual")            .addScalar("num", StandardBasicTypes.BIG_INTEGER);    return ((BigInteger) query.uniqueResult()).longValue();}

Thanks to the posters here: springsource_forum

I found the solution:

public class DefaultPostgresKeyServer{    private Session session;    private Iterator<BigInteger> iter;    private long batchSize;    public DefaultPostgresKeyServer (Session sess, long batchFetchSize)    {        this.session=sess;        batchSize = batchFetchSize;        iter = Collections.<BigInteger>emptyList().iterator();    }        @SuppressWarnings("unchecked")        public Long getNextKey()        {            if ( ! iter.hasNext() )            {                Query query = session.createSQLQuery( "SELECT nextval( 'mySchema.mySequence' ) FROM generate_series( 1, " + batchSize + " )" );                iter = (Iterator<BigInteger>) query.list().iterator();            }            return iter.next().longValue() ;        }}