Question

Is it possible to use a single Transaction boundary for Hibernate Session and a plain JDBC query. ?
The database and the datasource configurations are similar for both.

Answer 1

Yes. Use HibernateTransactionManager. Below is taken from its javadoc

This implementation is appropriate for applications that solely use
Hibernate for transactional data access, but it also supports direct
data source access within a transaction (i.e. plain JDBC code working
with the same DataSource). This allows for mixing services that access
Hibernate (including transactional caching) and services that use
plain JDBC (without being aware of Hibernate)! Application code needs
to stick to the same simple Connection lookup pattern as with
DataSourceTransactionManager (i.e. DataSourceUtils.getConnection or
going through a TransactionAwareDataSourceProxy).

Note that to be able to register a DataSource’s Connection for plain
JDBC code, this instance needs to be aware of the DataSource (see
setDataSource). The given DataSource should obviously match the one
used by the given SessionFactory. To achieve this, configure both to
the same JNDI DataSource, or preferably create the SessionFactory with
LocalSessionFactoryBean and a local DataSource (which will be
autodetected by this transaction manager).