configure hibernate with embedded tomcat 7 programmatically

Question

I am trying to configure a embedded tomcat instance in my app without any configuration files.

I have done some research and based upon this long tutorial and a shorter one i extracted this steps:

1. Create a ServletContextListener

   @WebListener //some articles on the web mentioned, that this would add the 
   //Listener automatically to the app context, but i cant believe that this works in my case
   public class HibernateListener implements ServletContextListener {
   
       public void contextInitialized(ServletContextEvent event) {
           HibernateUtil.getSessionFactory(); // create a factory
       }
   
       public void contextDestroyed(ServletContextEvent event) {
           HibernateUtil.getSessionFactory().close(); // free resources
       }
   }
   

2. Add that Listener to the app context

   Context rootCtx = tomcat.addContext("", base.getAbsolutePath());
   rootCtx.getServletContext().addListener("com.example.listeners.HibernateListener");
   
   tomcat.start();
   tomcat.getServer().await();
   

3. Implement the HibernateUtil class with the necessary configuration

   public class HibernateUtil {
   
       private static final SessionFactory sessionFactory;
   
       static {
           try {
               //should i call .configure() on the returned Configuration here?                
               sessionFactory = getConfiguration()
                       .buildSessionFactory();
           } catch (Throwable ex) {
               System.err.println("Initial SessionFactory creation failed." + ex);
               throw new ExceptionInInitializerError(ex);
           }
   
       }
   
       private static Configuration getConfiguration(){
           Configuration c = new Configuration();
   
           c.setProperty("hibernate.connection.url", "jdbc:hsqldb:hsql://localhost:1234/mydb1");
           c.setProperty("hibernate.connection.username", "SA");
           c.setProperty("hibernate.connection.password", "");
           c.setProperty("hibernate.connection.driver_class", "org.hsqldb.jdbcDriver");
   
   
           c.setProperty("dialect", "org.hibernate.dialect.HSQLDialect");
           c.setProperty("cache.provider_class", "org.hibernate.cache.NoCacheProvider");
           c.setProperty("cache.use_query_cache", "false");
           c.setProperty("cache.use_minimal_puts", "false");
           c.setProperty("max_fetch_depth", "3");
   
           c.setProperty("show_sql", "true");
           c.setProperty("format_sql", "true");
           c.setProperty("hbm2ddl.auto", "create");
   
           c.addPackage("com.example.models");
           c.addAnnotatedClass(MyClass.class);
   
           return c;
       }
   
       public static SessionFactory getSessionFactory() {
           return sessionFactory;
       }
   }
   

4. Now i should somehow work with MyClass to create and retrieve data from the linked database through hibernate, right? (right now i am not sure, how exactly, but thats not the point here)

But unfortunately i am getting a NullPointerException when im trying to add the listener to tomcat

Exception in thread "main" java.lang.NullPointerException at org.apache.catalina.core.ApplicationContext.addListener(ApplicationContext.java:1278) at org.apache.catalina.core.ApplicationContextFacade.addListener(ApplicationContextFacade.java:649)

which points to the line rootCtx.getServletContext().addListener("com.example.listeners.HibernateListener");

EDIT 1

But if i am running hibernate standalone (without tomcat) it works fine. The Data is being saved without errors!

In HibernateUtil

public static void main(String[] args) {
    MyClass mycls = new MyClass();

    mycls.setMyProperty("My Property");
    Session session = getSessionFactory().openSession();
    Transaction transaction = session.beginTransaction();
    session.save(mycls);
    transaction.commit();
}

So the way i am configuring hibernate is fine i think. The error has something to do with the listener adding...

What am i doing wrong here?

Answer 1

After a deep digging in the source code of Tomcat I have found one possible solution:

rootCtx.addApplicationListener(new ApplicationListener("com.example.listeners.HibernateListener", false));

It does what I needed!

Answer 2

I think you have missing the invocation of the method cinfigure() of the configuraton c right after your initialisation.

So it should look like this::

 SessionFactory sessionFactory =  getConfiguration().confgure().buildSessionFactory();

or

c = getConfiguration();
sessionFactory = c.configure().buildSessionFactory();

UPDATE

In order to add complete properties at runtim you can create a Prperties object and use the method.

  configuration.buildSettings(Properties props)

I am not sure but using this approach it could be pssible that hibernate not looks for the hibernate.cfg.xml or .properties within classpath .

UPDATE

What you can try additionally to invoke your getConfiguration method within the getSessionFactory method instead of calling it within the static initializer of the HibernateUtil expliciteLy

public static getSessionFactory() {
    Configuration c = getConfiguration();
    sessionFactory = c.buildSessionFactory();
    return sessionFactory;
}