Session session = HibernateUtil.getSessionFactory().openSession();
   Transaction tx = session.beginTransaction();   
   List< .. > l = (List< .. >)session.createQuery(" ... ").list();
   tx.commit();
   session.close();
   HibernateUtil.shutdown();

   Session session = HibernateUtil.getSessionFactory().openSession();
   Transaction tx = session.beginTransaction();   
   List< .. > l = (List< .. >)session.createQuery(" ... ").list();
   tx.commit();
   session.close();
   HibernateUtil.shutdown();

Exception in thread "AWT-EventQueue-0" org.hibernate.exception.GenericJDBCException: Cannot open connection
   at org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:140)
   at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:128)
   at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66)
   at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:52)
   at org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:449)
   at org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:167)
   at org.hibernate.jdbc.JDBCContext.connection(JDBCContext.java:160)
   at org.hibernate.transaction.JDBCTransaction.begin(JDBCTransaction.java:81)
   at org.hibernate.impl.SessionImpl.beginTransaction(SessionImpl.java:1473)
   at (myapp)
   at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
   at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
   at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
   at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
   at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
   at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
   at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
   at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
Caused by: java.sql.SQLException: com.mchange.v2.c3p0.PoolBackedDataSource@aec7d9d6 [ connectionPoolDataSource -> com.mchange.v2.c3p0.WrapperConnectionPoolDataSource@dba6e7f2 [ acquireIncrement -> 3, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, debugUnreturnedConnectionStackTraces -> false, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, identityToken -> 1hge13a8cc0yolv1x95331|4d16318b, idleConnectionTestPeriod -> 3000, initialPoolSize -> 5, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 300, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 20, maxStatements -> 50, maxStatementsPerConnection -> 0, minPoolSize -> 5, nestedDataSource -> com.mchange.v2.c3p0.DriverManagerDataSource@8112f8b5 [ description -> null, driverClass -> null, factoryClassLocation -> null, identityToken -> 1hge13a8cc0yolv1x95331|43f4ebd, jdbcUrl -> jdbc:postgresql:hostname, properties -> {user=******, password=******} ], preferredTestQuery -> null, propertyCycle -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, usesTraditionalReflectiveProxies -> false; userOverrides: {} ], dataSourceName -> null, factoryClassLocation -> null, identityToken -> 1hge13a8cc0yolv1x95331|30b48b11, numHelperThreads -> 3 ] has been closed() -- you can no longer use it.
   at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.assertCpds(AbstractPoolBackedDataSource.java:447)
   at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getPoolManager(AbstractPoolBackedDataSource.java:459)
   at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:128)
   at org.hibernate.connection.C3P0ConnectionProvider.getConnection(C3P0ConnectionProvider.java:78)
   at org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:446)
   ... 14 more

public class HibernateUtil {

   private static SessionFactory sessionFactory;

   static {
      try {
         sessionFactory = new Configuration().configure().buildSessionFactory();
         
      } catch (Throwable ex) {
         throw new ExceptionInInitializerError(ex);
      }
   }

   public static SessionFactory getSessionFactory() {
      // Alternatively, we could look up in JNDI here
      return sessionFactory;
   }

   public static void shutdown() {
      // Close caches and connection pools
      getSessionFactory().close();
   }
}

   <!-- Use the C3P0 connection pool provider -->
   <property name="hibernate.connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider</property>
   <property name="hibernate.c3p0.min_size">5</property>
   <property name="hibernate.c3p0.max_size">20</property>
   <property name="hibernate.c3p0.timeout">300</property>
   <property name="hibernate.c3p0.max_statements">50</property>
   <property name="hibernate.c3p0.idle_test_period">3000</property>