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Following 'fans xnet's excellant advise i did create a factory. I even (eventually) worked out what to put in it!

In order to build an EMF you need to do something like:

{code}

public EntityManagerFactory buildEntityManagerFactory(DataSource datasource) {

        Ejb3Configuration ejbconf = new Ejb3Configuration();

        ejbconf.setDataSource(datasource);

        ejbconf.setProperty("hibernate.dialect", "org.hibernate.dialect.MySQL5InnoDBDialect");

        ejbconf.setProperty("hibernate.show_sql", "false");

        //Make transactionally aware

        ejbconf.setProperty("hibernate.transaction.manager_lookup_class", "org.hibernate.transaction.JBossTransactionManagerLookup");

        ejbconf.setProperty("jta.UserTransaction", "java:comp/UserTransaction");

        ejbconf.setProperty("hibernate.current_session_context_class", "jta");

        ejbconf.setProperty(HibernatePersistence.TRANSACTION_TYPE, PersistenceUnitTransactionType.JTA.name());

        //Add caching

        ejbconf.setProperty("hibernate.cache.provider_class", "HibernateEhCacheProviderClass");

        ejbconf.setProperty("hibernate.cache.use_second_level_cache", "true");

        ejbconf.setProperty("net.sf.ehcache.configurationResourceName", "META-INF/ehcache.xml");

        //Add you entity beans here

        ejbconf.addAnnotatedClass(SomeEntityBean.class);

        return  ejbconf.buildEntityManagerFactory();

{code}

Knocking up a datasource with DBCP looks like:

{code}

    public DataSource buildDatasource(String connectionUrl) {

        // Create base connection factory that produces raw db connections.

        ConnectionFactory connectionFactory = new DriverManagerConnectionFactory(connectionUrl, libraryUser,

                libraryPassword);

        // Object pool for pooling raw connections

        GenericObjectPool connPool = new GenericObjectPool();

        connPool.setMaxActive(maxShardConns);

        connPool.setMinIdle(minShardConns);

        connPool.setMaxIdle(maxIdleConns);

        connPool.setMinEvictableIdleTimeMillis(shardConnTimeOutMins * 60 * 1000);

        connPool.setTestOnBorrow(true);

        connPool = new InstrumentedObjectPool(extractServerName(connectionUrl), connPool);

        String connectionValidationSql = "SELECT 1;";

        KeyedObjectPoolFactory preparedStatementPool = null;

        Boolean defaultConnectionsToReadOnly = false;

        Boolean defaultConnectionsToAutoCommit = false;

        TransactionManager transactionManager;

        try {

            transactionManager = (TransactionManager) InitialContext.doLookup("java:/TransactionManager");

        } catch (NamingException e) {

            throw new RuntimeException("Unable to lookup transaction manager", e);

        }

        LocalXAConnectionFactory transactionFactory = new LocalXAConnectionFactory(transactionManager,

                connectionFactory);

        // Create factory to manage the connectionPool

        PoolableManagedConnectionFactory poolableConnectionFactory = new PoolableManagedConnectionFactory(

                transactionFactory, connPool, preparedStatementPool, connectionValidationSql,

                defaultConnectionsToReadOnly, defaultConnectionsToAutoCommit);

        ManagedDataSource dataSource = new ManagedDataSource(connPool, transactionFactory.getTransactionRegistry());

        return dataSource;

{code}

Using these in combination will give you a transactionally aware EMF with connection pooling.