2011-04-20 10:20:57,016 ["http-bio-8080"-exec-7] ERROR org.hibernate.AssertionFailure - an assertion failure occured (this may indicate a bug in Hibernate, but is more likely due to unsafe use of the session)
java.lang.NullPointerException
    at org.hibernate.action.EntityVerifyVersionProcess.doBeforeTransactionCompletion(EntityVerifyVersionProcess.java:56)
    at org.hibernate.engine.ActionQueue$BeforeTransactionCompletionProcessQueue.beforeTransactionCompletion(ActionQueue.java:543)
    at org.hibernate.engine.ActionQueue.beforeTransactionCompletion(ActionQueue.java:216)
    at org.hibernate.impl.SessionImpl.beforeTransactionCompletion(SessionImpl.java:571)
    at org.hibernate.jdbc.JDBCContext.beforeTransactionCompletion(JDBCContext.java:250)
    at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:138)
    at com.innovigent.ptaserver.HibernateSessionRequestFilter.doFilter(HibernateSessionRequestFilter.java:38)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:244)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:161)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:550)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:380)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:243)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:188)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:166)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:288)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
org.hibernate.AssertionFailure: Unable to perform beforeTransactionCompletion callback
    at org.hibernate.engine.ActionQueue$BeforeTransactionCompletionProcessQueue.beforeTransactionCompletion(ActionQueue.java:549)
    at org.hibernate.engine.ActionQueue.beforeTransactionCompletion(ActionQueue.java:216)
    at org.hibernate.impl.SessionImpl.beforeTransactionCompletion(SessionImpl.java:571)
    at org.hibernate.jdbc.JDBCContext.beforeTransactionCompletion(JDBCContext.java:250)
    at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:138)
    at com.innovigent.ptaserver.HibernateSessionRequestFilter.doFilter(HibernateSessionRequestFilter.java:38)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:244)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:161)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:550)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:380)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:243)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:188)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:166)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:288)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException
    at org.hibernate.action.EntityVerifyVersionProcess.doBeforeTransactionCompletion(EntityVerifyVersionProcess.java:56)
    at org.hibernate.engine.ActionQueue$BeforeTransactionCompletionProcessQueue.beforeTransactionCompletion(ActionQueue.java:543)
    ... 21 more

public class HibernateSessionRequestFilter implements Filter {

    private static Logger log = LoggerFactory.getLogger(HibernateSessionRequestFilter.class);

    private SessionFactory sf;

    @Override
    public void destroy() {
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
        FilterChain chain) throws IOException, ServletException {

    try{
    log.debug("Starting a database transaction");
    sf.getCurrentSession().beginTransaction();
    chain.doFilter(request, response);

    log.debug("Comitting the database transaction");
    sf.getCurrentSession().getTransaction().commit();
    }catch(Throwable ex){
        ex.printStackTrace();

            try {
                if (sf.getCurrentSession().getTransaction().isActive()) {
                    log.debug("Trying to rollback database transaction after exception");
                    sf.getCurrentSession().getTransaction().rollback();
                }
            } catch (Throwable rbEx) {
                log.error("Could not rollback transaction after exception!", rbEx);
            }

            // Let others handle it... maybe another interceptor for exceptions?
            throw new ServletException(ex);
    }

    }

    @Override
    public void init(FilterConfig arg0) throws ServletException {
    log.debug("Initializing HibernateSessionRequestFilter");
    sf = HibernateUtil.getSessionFactory();
    }

}

<hibernate-configuration>
<session-factory>
  <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
  <property name="hibernate.connection.password">password</property>
  <property name="hibernate.connection.url">jdbc:mysql://localhost/db</property>
  <property name="hibernate.connection.username">db</property>
  <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
   <property name="hibernate.current_session_context_class">thread</property>

... some reference to mapping xml files ...

</session-factory>
</hibernate-configuration>

@Version
 public long version;